Facts on File DICTIONARY of CHEMISTRY

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The Facts On File DICTIONARY of CHEMISTRY

Fourth Edition

Edited by John Daintith The Facts On File Dictionary of Chemistry Fourth Edition

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This book is printed on acid-free paper. PREFACE

This dictionary is one of a series designed for use in schools. It is intended for students of chemistry, but we hope that it will also be helpful to other science students and to anyone interested in science. Facts On File also publishes dictionaries in a variety of disciplines, including biology, physics, mathematics, forensic science, weather and climate, marine science, and space and astronomy.

The Facts On File Dictionary of Chemistry was first published in 1980 and the third edition was published in 1999. This fourth edition of the dictionary has been extensively revised and extended. The dictionary now contains over 3,000 headwords covering the terminology of modern chemistry. A totally new feature of this edition is the inclusion of over 1,700 pronunciations for terms that are not in everyday use. A number of appendixes have been included at the end of the book containing useful information, including a list of chemical elements and a periodic table. There is also a list of Web sites and a bibliography. A guide to using the dictionary has also been added to this latest version of the book.

We would like to thank all the people who have cooperated in producing this book. A list of contributors is given on the acknowledgments page. We are also grateful to the many people who have given additional help and advice.

v ACKNOWLEDGMENTS

Contributors

Julia Brailsford B.Sc. John Clark B.Sc. John Connor B.Sc. Derek Cooper Ph.D. F.R.I.C. Rich Cutler B.Sc. D.E. Edwards B.Sc. M.Sc. Richard Hadfield B.Sc. Valerie Illingworth B.Sc. M.Phil. Alan Isaacs B.Sc. Ph.D. Elizabeth Martin M.A. P.R. Mercer B.A. T.C. R.S. Smith B.Sc. C.Chem. M.R.I.C. Derek Stefaniw B.Sc. Ph.D. Elizabeth Tootil M.Sc. J. Truman B.Sc. David Eric Ward B.Sc. M.Sc. Ph.D.

Pronunciations

William Gould B.A.

Note Unless otherwise stated, the melting and boiling points given in the dictionary are at standard pressure. Relative densities of liquids are at standard pressure with the liquid at 20°C relative to water at 4°C. Relative densities of gases are relative to air, both gases being at standard temperature and pressure.

The following abbreviations are used in the text:

p.n. proton number (atomic number) r.a.m. relative atomic mass (atomic weight)

vi CONTENTS

Preface v

Acknowledgments vi

Guide to Using the Dictionary viii

Pronunciation Key x

Entries A to Z 1

Appendixes I. Carboxylic Acids 297 II. Amino Acids 299 III. Sugars 302 IV. Nitrogenous Bases 303 and Nucleosides V. The Chemical Elements 305 VI. The Periodic Table 307 VII. The Greek Alphabet 308 VIII. Web Sites 309

Bibliography 310

vii GUIDE TO USING THE DICTIONARY

The main features of dictionary entries are as follows.

Headwords The main term being defined is in bold type:

acid A substance that gives rise to hydrogen ions when dissolved in water.

Plurals Irregular plurals are given in brackets after the headword.

quantum (pl. quanta) A definite amount of energy released or absorbed in a process.

Variants Sometimes a word has a synonym or alternative spelling. This is placed in brackets after the headword, and is also in bold type:

promoter (activator) A substance that improves the efficiency of a catalyst.

Here, ‘activator’ is another word for promoter. Generally, the entry for the synonym consists of a simple cross-reference:

activator See promoter.

Abbreviations Abbreviations for terms are treated in the same way as variants:

electron spin resonance (ESR) A similar technique to nuclear magnetic resonance, but applied to unpaired electrons ...

The entry for the synonym consists of a simple cross-reference:

ESR See electron spin resonance.

Formulas Chemical formulas are also placed in brackets after the headword. These are in normal type:

potassium iodide (KI) A white ionic solid....

Here, KI is the chemical formula for potassium iodide.

viii Multiple definitions Some terms have two or more distinct senses. These are numbered in bold type

abundance 1. The relative amount of a given element among others; for example, the abundance of oxygen in the Earth’s crust is approximately 50% by mass. 2. The amount of a nuclide (stable or radioactive) relative to other nuclides of the same element in a given sample.

Cross-references These are references within an entry to other entries that may give additional useful information. Cross-references are indicated in two ways. When the word appears in the definition, it is printed in small capitals:

boron nitride (BN) A compound formed by heating BORON in nitrogen…

In this case the cross-reference is to the entry for `boron’.

Alternatively, a cross-reference may be indicated by ‘See’, ‘See also’, or ‘Compare’, usually at the end of an entry:

boron trifluoride (BF3) A colorless fuming gas made by… See boron trichloride.

Hidden entries Sometimes it is convenient to define one term within the entry for another term:

charcoal An amorphous form of carbon made by… Activated charcoal is charcoal heated to…

Here, ‘activated charcoal’ is a hidden entry under charcoal, and is indicated by italic type. The entry for ‘activated charcoal’ consists of a simple cross-reference:

activated charcoal See charcoal.

Pronunciations Where appropriate pronunciations are indicated immediately after the headword, en- closed in forward slashes:

deuteride /dew-ter-ÿd/ A compound of deuterium…

Note that simple words in everyday language are not given pronunciations. Also headwords that are two-word phrases do not have pronunciations if the component words are pronounced elsewhere in the dictionary.

ix Pronunciation Key

Bold type indicates a stressed syllable. In pronunciations, a consonant is sometimes doubled to prevent accidental mispronunciation of a syllable resembling a familiar word; for example, /ass-id/ (acid), rather than /as-id/ and /ul-tră- sonn-iks/ (ultrasonics), rather than /ul-tră-son-iks/. An apostrophe is used: (a) between two consonants forming a syllable, as in /den-t’l/ (dental), and (b) between two letters when the syllable might otherwise be mis- pronounced through resembling a familiar word, as in /th’e-ră-pee/ (therapy) and /tal’k/ (talc). The symbols used are:

/a/ as in back /bak/, active /ak-tiv/ /ng/ as in sing /sing/ /ă/ as in abduct /ăb-dukt/, gamma /gam-ă/ /nk/ as in rank /rank/, bronchus /bronk-ŭs/ /ah/ as in palm /pahm/, father /fah-ther/, /o/ as in pot /pot/ /air/ as in care /kair/, aerospace /air-ŏ- /ô/ as in dog /dôg/ spays/ /ŏ/ as in buttock /but-ŏk/ /ar/ as in tar /tar/, starfish /star-fish/, heart /oh/ as in home /hohm/, post /pohst/ /hart/ /oi/ as in boil /boil/ /aw/ as in jaw /jaw/, gall /gawl/, taut /tawt/ /oo/ as in food /food/, croup /kroop/, fluke /ay/ as in mania /may-niă/ ,grey /gray/ /flook/ /b/ as in bed /bed/ /oor/ as in pruritus /proor-ÿ-tis/ /ch/ as in chin /chin/ /or/ as in organ /or-găn/, wart /wort/ /d/ as in day /day/ /ow/ as in powder /pow-der/, pouch /e/ as in red /red/ /powch/ /ĕ/ as in bowel /bow-ĕl/ /p/ as in pill /pil/ /ee/ as in see /see/, haem /heem/, caffeine /r/ as in rib /rib/ /kaf-een/, baby /bay-bee/ /s/ as in skin /skin/, cell /sel/ /eer/ as in fear /feer/, serum /seer-ŭm/ /sh/ as in shock /shok/, action /ak-shŏn/ /er/ as in dermal /der-măl/, labour /lay-ber/ /t/ as in tone /tohn/ /ew/ as in dew /dew/, nucleus /new-klee-ŭs/ /th/ as in thin /thin/, stealth /stelth/ /ewr/ as in epidural /ep-i-dewr-ăl/ /th/ as in then /then/, bathe /bayth/ /f/ as in fat /fat/, phobia /foh-biă/, rough /u/ as in pulp /pulp/, blood /blud/ /ruf/ /ŭ/ as in typhus /tÿ-fŭs/ /g/ as in gag /gag/ /û/ as in pull /pûl/, hook /hûk/ /h/ as in hip /hip/ /v/ as in vein /vayn/ /i/ as in fit /fit/, reduction /ri-duk-shăn/ /w/ as in wind /wind/ /j/ as in jaw /jaw/, gene /jeen/, ridge /rij/ /y/ as in yeast /yeest/ /k/ as in kidney /kid-nee/, chlorine /klor- /ÿ/ as in bite /bÿt/, high /hÿ/, hyperfine /hÿ- een/, crisis /krÿ-sis/ per-fÿn/ /ks/ as in toxic /toks-ik/ /yoo/ as in unit /yoo-nit/, formula /form- /kw/ as in quadrate /kwod-rayt/ yoo-lă/ /l/ as in liver /liv-er/, seal /seel/ /yoor/ as in pure /pyoor/, ureter /yoor-ee- /m/ as in milk /milk/ ter/ /n/ as in nit /nit/ /ÿr/ as in fire /fÿr/

x A

AAS See atomic absorption spec- modynamic temperature; 0 kelvin or troscopy. –273.15°C. absolute alcohol Pure alcohol (ethanol). absorption A process in which a gas is taken up by a liquid or solid, or in which a absolute configuration A particular liquid is taken up by a solid. In absorption, molecular configuration of a CHIRAL mole- the substance absorbed goes into the bulk cule, as denoted by comparison with a ref- of the material. Solids that absorb gases or erence molecule or by some sequence rule. liquids often have a porous structure. The There are two systems for expressing ab- absorption of gases in solids is sometimes solute configuration in common use: the called sorption. Compare adsorption. D–L convention and the R–S convention. See optical activity. absorption indicator (adsorption indicator) An indicator used for titrations that absolute temperature Symbol: T A involve a precipitation reaction. The temperature defined by the relationship: method depends upon the fact that at the T = θ + 273.15 equivalence point there is a change in the where θ is the Celsius temperature. The ab- nature of the ions absorbed by the precipi- solute scale of temperature was a funda- tate particles. Fluorescein – a fluorescent mental scale based on Charles’ law applied compound – is commonly used. For exam- to an ideal gas: ple, in the titration of sodium chloride so- αθ V = V0(1 + ) lution with added silver nitrate, silver θ where V is the volume at temperature , V0 chloride is precipitated. Sodium ions and the volume at 0, and α the thermal expan- chloride ions are absorbed in the precipi- sivity of the gas. At low pressures (when tate. At the end point, silver ions and ni- real gases show ideal behavior) α has the trate ions are in slight excess and silver ions value 1/273.15. Therefore, at θ = –273.15 are then absorbed. If fluorescein is present, the volume of the gas theoretically negative fluorescein ions absorb in prefer- becomes zero. In practice, of course, sub- ence to nitrate ions, producing a pink com- stances become solids at these tempera- plex. tures. However, the extrapolation can be used for a scale of temperature on which absorption spectrum See spectrum. –273.15°C corresponds to 0° (absolute zero). The scale is also known as the ideal- abundance 1. The relative amount of a gas scale; on it temperature intervals were given element among others; for example, called degrees absolute (°A) or degrees the abundance of oxygen in the Earth’s Kelvin (°K), and were equal to the Celsius crust is approximately 50% by mass. degree. It can be shown that the absolute 2. The amount of a nuclide (stable or ra- temperature scale is identical to the ther- dioactive) relative to other nuclides of the modynamic temperature scale (on which same element in a given sample. The nat- the unit is the kelvin). ural abundance is the abundance of a nuclide as it occurs naturally. For instance, absolute zero The zero value of ther- chlorine has two stable isotopes of masses

1 accelerator

35 and 37. The abundance of 35Cl is acetate /ass-ĕ-tayt/ See ethanoate. 75.5% and that of 37Cl is 24.5%. For some elements the abundance of a particular nu- acetic acid /ă-see-tik, ă-set-ik/ See clide depends on the source. ethanoic acid. accelerator A catalyst added to increase acetone /ass-ĕ-tohn/ See propanone. the rate of cross-linking reactions in polymers. acetonitrile /ass-ĕ-toh-nÿ-trăl, ă-see-toh-, -tril, -trÿl/ See methyl cyanide. acceptor /ak-sep-ter, -tor/ The atom or group to which a pair of electrons is do- acetophenone /ass-ĕ-toh-fee-nohn, ă-see- nated in a coordinate bond. Pi-acceptors toh-/ See phenyl methyl ketone. are compounds or groups that accept electrons into pi, p or d orbitals. acetylation /ă-set’l-ay-shŏn/ See acylation. accumulator (secondary cell; storage bat- acetyl chloride /ass-ĕ-t’l, ă-see-t’l/ See tery) An electric cell or battery that can ethanoyl chloride. be charged by passing an electric current through it. The chemical reaction in the cell acetylene /ă-set-ă-leen, -lin/ See ethyne. is reversible. When the cell begins to run down, current in the opposite direction acetyl group See ethanoyl group. will convert the reaction products back into their original forms. The most com- acetylide /ă-set-ă-lÿd/ See carbide. mon example is the LEAD-ACID ACCUMULA- TOR, used in vehicle batteries. acetylsalicylic acid /ass-ĕ-t’l-sal-ă-sil-ik, ă-see-t’l-/ See aspirin. acenaphthene /as-ĕ-naf-th’een, -nap-/ (C12H10) A colorless crystalline deriva- Acheson process /ach-ĕ-s’n/ See carbon. tive of naphthalene, used in producing some dyes. achiral /ă-kÿr-ăl/ Describing a molecule that does not exhibit optical activity. 12 acid A substance that gives rise to hydrogen ions when dissolved in water. Strictly, these ions are hydrated, known as hydroxonium or hydronium ions, and are + usually given the formula H3O . An acid in Acenaphthene solution will have a pH below 7. This definition does not take into account the com- petitive behavior of acids in solvents and it acetal /ass-ĕ-tal/ A type of organic com- refers only to aqueous systems. The Lowry– pound formed by addition of an alcohol to Brønsted theory defines an acid as a sub- an aldehyde. Addition of one alcohol mol- stance that exhibits a tendency to release a ecule gives a hemiacetal. Further addition proton, and a base as a substance that yields the full acetal. Similar reactions tends to accept a proton. Thus, when an occur with ketones to produce hemiketals acid releases a proton, the ion formed is the and ketals. conjugate base of the acid. Strong acids (e.g. HNO3) react completely with water + acetaldehyde /ass-ĕ-tal-dĕ-hÿd/ See to give H3O , i.e. HNO3 is stronger than + – ethanal. H3O and the conjugate base NO3 is weak. Weak acids (e.g. CH3COOH and acetamide /ass-ĕ-tam-ÿd, -id; ă-set-ĕ-mÿd, C6H5COOH) are only partly dissociated + -mid/ See ethanamide. because H3O is a stronger acid than the 2 acid salt

– free acids and the ions CH3COO and measure of the acidity, i.e. an acidic solu- – C6H5COO are moderately strong bases. tion is one in which the concentration of + The Lowry–Brønsted theory is named for H3O exceeds that in pure water at the the English chemist Thomas Martin Lowry same temperature; i.e. the pH is lower than (1874–1936) and the Danish physical 7. A pH of 7 is regarded as being neutral. chemist Johannes Nicolaus Brønsted (1879–1947). See also Lewis acid. acidic hydrogen A hydrogen atom in a molecule that enters into a dissociation acid anhydride A type of organic com- equilibrium when the molecule is dissolved ′ pound of general formula RCOOCOR , in a solvent. For example, in ethanoic acid ′ where R and R are alkyl or aryl groups. (CH COOH) the acidic hydrogen is the They are prepared by reaction of an acyl 3 one on the carboxyl group, –COOH. halide with the sodium salt of a carboxylic acid, e.g.: acidic oxide An oxide of a nonmetal RCOCl + R′COO–Na+ → RCOOCOR′ that reacts with water to produce an acid + NaCl Like the acyl halides, they are very reactive or with a base to produce a salt and water. acylating agents. Hydrolysis is to car- For example, sulfur(VI) oxide (sulfur triox- boxylic acids: ide) reacts with water to form sulfuric(VI) RCOOCOR′ + H O → RCOOH + acid: 2 → R′COOH SO3 + H2O H2SO4 See also acylation. and with sodium hydroxide to produce sodium sulfate and water: → SO3 + NaOH Na2SO4 + H2O R’ See also amphoteric; basic oxide. C O acidimetry /ass-ă-dim-ĕ-tree/ Volumet- O ric analysis or acid-base titration in which C O a standard solution of an acid is added to the unknown (base) solution plus the indi- R cator. Alkalimetry is the converse, i.e. the Acid anhydride structure base is in the buret.

acidity constant See dissociation con- acid–base indicator An indicator that stant. is either a weak base or a weak acid and whose dissociated and undissociated forms acid rain See pollution. differ markedly in color. The color change must occur within a narrow pH range. Ex- acid salt (acidic salt) A salt in which amples are methyl orange and phenolph- there is only partial replacement of the thalein. acidic hydrogen of an acid by metal or other cations. For polybasic acids the for- acid dyes The sodium salts of organic acids used in the dyeing of silks and wool. mulae are of the type NaHSO4 (sodium hy- They are so called because they are applied drogensulfate) and Na3H(CO3)2.2H2O from a bath acidified with dilute sulfuric or (sodium sesquicarbonate). For monobasic ethanoic acid. acids such as HF the acid salts are of the form KHF2 (potassium hydrogen fluoride). acid halide See acyl halide. Although the latter were at one time formulated as a normal salt plus excess acid acidic Having a tendency to release a (i.e. KF.HF) it is preferable to treat these as proton or to accept an electron pair from a hydrogen-bonded systems of the type K+ donor. In aqueous solutions the pH is a (F–H–F)–.

3 acid value acid value A measure of the free acid ores and the metal can be obtained by represent in fats, oils, resins, plasticizers, and ducing the trifluoride with lithium. It can solvents, defined as the number of mil- be produced by neutron bombardment of ligrams of potassium hydroxide required radium and is used as a source of alpha to neutralize the free acids in one gram of particles. The metal glows in the dark; it re- the substance. acts with water to produce hydrogen. Symbol: Ac; m.p. 1050±50°C; b.p. acridine /ak-ri-deen/ (C12H9N) A color- 3200±300°C; r.d. 10.06 (20°C); p.n. 89; less crystalline heterocyclic compound most stable isotope 227Ac (half-life 21.77 with three fused rings. Derivatives of acri- years). dine are used as dyes and biological stains. actinoids /ak-tă-noidz/ (actinides)A N group of 15 radioactive elements whose electronic configurations display filling of the 5f level. As with the lanthanoids, the first member, actinium, has no f electrons (Ac [Rn]6d17s2) but other members also Acridine show deviations from the smooth trend of f-electron filling expected from simple considerations, e.g. thorium Th [Rn]6d27s2, Acrilan /ak-ră-lan/ (Trademark) A syn- berkelium Bk [Rn]5f86d17s2. The actinoids thetic fiber that consists of a copolymer of are all radioactive and their chemistry is 1-cyanoethene (acrylonitrile, vinyl often extremely difficult to study. In gen- cyanide) and ethenyl ethanoate (vinyl ac- eral, artificial methods using high-energy etate). bombardment are used to generate them. See also transuranic elements. acrolein /ă-kroh-lee-in/ See propenal. activated charcoal See charcoal. acrylic acid /ă-kril-ik/ See propenoic acid. activated complex The partially bonded system of atoms in the transition acrylic resin A synthetic resin made by state of a chemical reaction. polymerizing an amide or ester derivative of 2-propenoic acid (acrylic acid). Exam- activation energy Symbol: Ea The min- ples of acrylic materials are Acrilan (from imum energy a particle, molecule, etc., propenonitrile) and Plexiglas (polymethyl- must acquire before it can react; i.e. the en- methacrylate). Acrylic resins are also used ergy required to initiate a reaction regard- in paints. less of whether the reaction is exothermic acrylonitrile /ak-ră-loh-nÿ-trăl, -tril, -trÿl, or endothermic. Activation energy is often ă-kril-oh-/ See propenonitrile. represented as an energy barrier that must be overcome if a reaction is to take place. actinic radiation /ak-tin-ik/ Radiation See Arrhenius equation. that can cause a chemical reaction; for example, ultraviolet radiation is actinic. activator See promoter. actinides /ak-tă-nÿdz/ See actinoids. active mass See mass action; law of. actinium /ak-tin-ee-ŭm/ A soft silvery- active site 1. a site on the surface of a white radioactive metallic element that is catalyst at which catalytic activity occurs the first member of the actinoid series. It or at which the catalyst is particularly ef- occurs in minute quantities in uranium fective.

4 adenine

2. The position on the molecule of an en- acyl group The group of atoms RCO–. zyme that binds to the substrate when the ENZYME acts as a catalyst. acyl halide (acid halide) A type of organic compound of the general formula activity 1. Symbol: a Certain thermody- RCOX, where X is a halogen (acyl chlo- namic properties of a solvated substance ride, acyl bromide, etc.). are dependent on its concentration (e.g. its Acyl halides can be prepared by the re- tendency to react with other substances). action of carboxylic acid with a halogenat- Real substances show departures from ing agent. Commonly, phosphorus halides ideal behavior and a corrective concentra- are used (e.g. PCl5) or a sulfur dihalide tion term – the activity – has to be intro- oxide (e.g. SOCl2): RCOOH + PCl → RCOCl + POCl duced into equations describing real 5 3 + HCl solvated systems. RCOOH + SOCl → RCOCl + SO 2. Symbol: A The average number of atoms 2 2 + HCl disintegrating per unit time in a radioactive The acyl halides have irritating vapors substance. and fume in moist air. They are very reactive to the hydrogen atom of compounds activity coefficient Symbol: f A mea- containing hydroxyl (–OH) or amine sure of the degree of deviation from ideal- (–NH2) groups. See acylation. ity of a solvated substance, defined as: a = fc where a is the activity and c the concentration. For an ideal solute f = 1; for real sys- O tems f can be less or greater than unity. acyclic /ay-sÿ-klik, -sik-lik/ Describing a C compound that is not cyclic (i.e. a com- RCl pound that does not contain a ring in its Acyl halide: an acyl chloride molecules). acyl anhydride /ass-ăl, ay-săl/ See acid anhydride. addition polymerization See polymerization. acylating agent /ass-ă-layt-ing/ See acylation. addition reaction A reaction in which additional atoms or groups of atoms are in- acylation /ass-ă-lay-shŏn/ A reaction troduced into an unsaturated compound, that introduces the acyl group (RCO–). such as an alkene or ketone. A simple example is the addition of bromine across the Acylating agents are acyl halides (R.CO.X) double bond in ethene: and acid anhydrides (R.CO.O.CO.R), H C:CH + Br → BrH CCH Br which react with such nucleophiles as 2 2 2 2 2 Addition reactions can be induced ei- H2O, ROH, NH3, and RNH2. In these ther by electrophiles or by nucleophiles. compounds a hydrogen atom of a hydroxyl See also electrophilic addition; nucleophilic or amine group is replaced by the RCO– addition. group. In acetylation the acetyl group (CH3CO–) is used. In benzoylation the adduct /ă-dukt/ See coordinate bond. benzoyl group (C6H5CO–) is used. Acyla- tion is used to prepare crystalline deriva- adenine /ad-ĕ-neen, -nin, -nÿn/ A ni- tives of organic compounds to identify trogenous base found in DNA and RNA. It them (e.g. by melting point) and to protect is also a constituent of certain coenzymes –OH groups in synthetic reactions. and when combined with the sugar ribose

5 adenosine it forms the nucleoside adenosine found in adsorption /ad-sorp-shŏn, -zorp-/A AMP, ADP, and ATP. Adenine has a process in which a layer of atoms or mole- purine ring structure. cules of one substance forms on the surface of a solid or liquid. All solid surfaces take adenosine /ă-den-ŏ-seen, -sin, ad-’n-ŏ- up layers of gas from the surrounding at- seen/ (adenine nucleoside)A NUCLEOSIDE mosphere. The adsorbed layer may be held formed from adenine linked to D-ribose by chemical bonds (chemisorption) or by with a β-glycosidic bond. It is widely found weaker van der Waals forces (physisorp- in all types of cell, either as the free nucle- tion). Compare absorption. oside or in combination in nucleic acids. Phosphate esters of adenosine, such as ATP, adsorption indicator See absorption are important carriers of energy in bio- indicator. chemical reactions. aerobic /air-oh-bik/ Describing a bio- adenosine diphosphate /dÿ-fos-fayt/ See chemical process that takes place only in ADP. the presence of free oxygen. Compare anaerobic. adenosine monophosphate /mon-oh- fos-fayt/ See AMP. aerosol See sol. adenosine triphosphate /trÿ-fos-fayt/ AES See atomic emission spectroscopy. See ATP. affinity The extent to which one sub- adiabatic change /ad-ee-ă-bat-ik/A stance is attracted to or reacts with an- change during which no energy enters or other. leaves the system. In an adiabatic expansion of a gas, me- afterdamp See firedamp. chanical work is done by the gas as its volume increases and the gas temperature falls. agate /ag-it, -ayt/ A hard microcrys- For an ideal gas undergoing a reversible talline form of the mineral chalcedony (a adiabatic change it can be shown that variety of quartz). Typically it has greenish γ pV = K1 or brownish bands of coloration, and is γ 1–γ T p = K2 used for making ornaments. Moss agate is γ–1 and TV = K3 not banded, but has mosslike patterns re- γ where K1, K2, and K3 are constants and is sulting from the presence of iron and man- the ratio of the principal specific heat ca- ganese oxides. Agate is used in instrument pacities. Compare isothermal change. bearings because of its resistance to wear. adipic acid /ă-dip-ik/ See hexanedioic agent orange A herbicide consisting of acid. a mixture of two weedkillers (2,4-D and 2,4,5-T), which was formerly used in war- ADP (adenosine diphosphate) A NUCLEO- fare to defoliate trees where an enemy may TIDE consisting of adenine and ribose with be hiding or to destroy an enemy’s crops. It two phosphate groups attached. See also also contains traces of the highly toxic ATP. chemical dioxin, which may cause cancers and birth defects. adsorbate /ad-sor-bayt, -zor-/ A substance that is adsorbed on a surface. See air The mixture of gases that surrounds adsorption. the Earth. The composition of dry air, by volume, is: adsorbent /ad-sor-bĕnt, -zor-/ The sub- nitrogen 78.08% stance on whose surface ADSORPTION takes oxygen 20.95% place. argon 0.93%

6 alcohol

carbon dioxide 0.03% which are monohydric). Examples are neon 0.0018% ethane-1,2-diol (ethylene glycol; (HOCH2- helium 0.0005% CH2OH) and propane-1,2,3-triol (glyc- krypton 0.0001% erol; HOCH2CH(OH)CH2OH). xenon 0.00001% Alcohols are further classified accord- Air also contains a variable amount of ing to the environment of the –C–OH water vapor, as well as particulate matter grouping. If the carbon atom is attached to (e.g. dust and pollen), and small amounts two hydrogen atoms, the compound is a of other gases. primary alcohol. If the carbon atom is attached to one hydrogen atom and two air gas See producer gas. other groups, it is a secondary alcohol. If the carbon atom is attached to three other alabaster A mineral form of gypsum groups, it is a tertiary alcohol. Alcohols can (CaSO4.2H2O). be prepared by: 1. Hydrolysis of HALOALKANES using aque- alanine /al-ă-neen, -nÿn/ See amino ous potassium hydroxide: acids. RI + OH– → ROH + I– 2. Reduction of aldehydes by nascent hy- albumen /al-byoo-mĕn/ The white of an drogen (from sodium amalgam in water): → egg, which consists mainly of albumin. See RCHO +2[H] RCH2OH albumin. The main reactions are: 1. Oxidation by potassium dichromate(VI) albumin /al-byoo-min/ A soluble protein in sulfuric acid. Primary alcohols give that occurs in many animal fluids, such as blood serum and egg white. H OH An ancient pseudoscience that alchemy C was the precursor of chemistry, dating from early Christian times until the 17th C H century. It combined mysticism and exper- H3 imental techniques. Many ancient al- chemists searched for the Philosopher’s primary (ethanol) stone – a substance that could transmute base metals into gold and produce the elixir of life, a universal remedy for all ills. H3C OH alcohol A type of organic compound of C the general formula ROH, where R is a hydrocarbon group. Examples of simple alco- H3C H hols are methanol (CH3OH) and ethanol (C2H5OH). secondary (propan-2-ol) Alcohols have the –OH group attached to a carbon atom that is not part of an aromatic ring: C6H5OH, in which the –OH group is attached to the ring, is thus a phe- H3C OH nol. Phenylmethanol (C6H5CH2OH) does have the characteristic properties of alco- C hols. Alcohols can have more than one –OH H3C CH3 group; those containing two, three or more such groups are described as dihydric, tri- tertiary (2-methylpropan-2-ol) hydric, and polyhydric respectively (as opposed to those containing one –OH group, Alcohols

7 aldehyde

→ aldehydes, which are further oxidized to C2H5CHO + HCN carboxylic acids: C2H5CH(OH)CN → → RCH2OH RCHO RCOOH 3. They form addition compounds (bisul- 1. Secondary alcohols are oxidized to ke- fite addition compounds) with the hy- tones. drogensulfate(IV) ion (hydrogensulfite; – 2. Formation of esters with acids. The re- HSO3 ): – → action, which is reversible, is catalyzed RCHO + HSO3 RCH(OH)(HSO3) by H+ ions: 4. They undergo CONDENSATION REACTIONS ′ ˆ ′ with such compounds as hydrazine, hy- ROH + R COOH R COOR + H2O 3. Dehydration over hot pumice (400°C) droxylamine, and their derivatives. to alkenes: 5. With alcohols they form hemiacetals → and ACETALS. RCH2CH2OH – H2O RCH:CH2 4. Reaction with sulfuric acid. Two types 6. They polymerize readily. Polymethanal of reaction are possible. With excess or methanal trimer can be formed from acid at 160°C dehdyration occurs to methanal depending on the conditions. give an alkene: Ethanal gives ethanal trimer or ethanal RCH CH OH + H SO → H O + tetramer. 2 2 2 4 2 See also Cannizzaro reaction; ketone. RCH2CH2.HSO4 → RCH2CH2.HSO4 RCH:CH2 + H2SO4 O 4. With excess alcohol at 140°C an ether is formed: R C → 2ROH ROR + H2O H See also acylation. Aldehyde aldehyde /al-dĕ-hÿd/ A type of organic compound with the general formula aldohexose /al-doh-heks-ohs/ An aldose RCHO, where the –CHO group (the alde- SUGAR with six carbon atoms. hyde group) consists of a carbonyl group attached to a hydrogen atom. Simple ex- aldol /al-dol, -dohl/ See aldol reaction. amples of aldehydes are methanal (formaldehyde, HCHO) and ethanal (ac- aldol reaction A reaction in which two etaldehyde, CH3CHO). molecules of aldehyde combine to give an Aldehydes are formed by oxidizing a aldol – i.e. a compound containing both primary alcohol. In the laboratory potas- aldehyde and alcohol functional groups. sium dichromate(VI) is used in sulfuric The reaction is base-catalyzed; the reaction acid. They can be further oxidized to car- of ethanal refluxed with sodium hydroxide boxylic acids. Reduction (using a catalyst gives: or nascent hydrogen from sodium amal- → 2CH3CHO CH3CH(OH)CH2CHO gam in water) produces the parent alcohol. The mechanism is similar to that of the Aldehydes undergo a number of reac- CLAISEN CONDENSATION: the first step is re- tions: moval of a proton to give a carbanion, 1. They act as reducing agents, being oxi- which subsequently attacks the carbon of dized to carboxylic acids in the process. the carbonyl group on the other molecule: – → – These reactions are used as tests for CH3CHO + OH CH2CHO + H2O. aldehydes using such reagents as Fehling’s solution and Tollen’s reagent aldopentose /al-doh-pen-tohs/ An al- (silver-mirror test). dose SUGAR with five carbon atoms. 2. They form addition compounds with hydrogen cyanide to give ‘cyanohy- aldose /al-dohs/A SUGAR containing an drins’. For example, propanal gives 2- aldehyde (CHO) or potential aldehyde hydroxybutanonitrile: group.

8 alkali metals alginic acid /al-jin-ik/ (algin; oxidizing). As the group is descended there (C6H8O6)n) A yellow-white organic solid is a gradual decrease in ionization potential that is found in brown algae. It is a com- and an increase in the size of the atoms; the plex polysaccharide and produces, in even group shows several smooth trends which very dilute solutions, a viscous liquid. Al- follow from this. For example, lithium re- ginic acid has various uses, especially in the acts in a fairly controlled way with water, food industry as a stabilizer and texture sodium ignites, and potassium explodes. agent. There is a general decrease in the following: melting points, heats of sublimation, alicyclic compound /al-ă-sÿ-klik, -sik- lattice energy of salts, hydration energy of lik/ An aliphatic cyclic compound, such M+, ease of decomposition of nitrates and as cyclohexane. carbonates, and heat of formation of the ‘-ide’ compounds (fluoride, hydride, oxide, aliphatic compound /al-ă-fat-ik/An carbide, chloride). organic compound with properties similar Lithium has the smallest ion and there- to those of the alkanes, alkenes, and fore the highest charge/size ratio and is po- alkynes and their derivatives. Most larizing with a tendency towards covalent aliphatic compounds have an open chain character in its bonding; the remaining ele- structure but some, such as cyclohexane ments form typical ionic compounds in and sucrose, have rings. The term is used in which ionization, M+X–, is regarded as distinction to aromatic compounds, which complete. The slightly anomalous position are similar to benzene. Compare aromatic of lithium is illustrated by the similarity of compound. its chemistry to that of magnesium. For example, lithium hydroxide is much less sol- alizarin /ă-liz-ă-rin/ (1,2-dihydroxyan- uble than the hydroxides of the other thraquinone) An important orange-red group 1 elements; lithium perchlorate is organic compound used in the dyestuffs insoluble in several organic solvents. Because dustry to produce red lakes. It occurs natu- of the higher lattice energies associated rally in the root of the plant madder and with smaller ions lithium hydride and ni- may also be synthesized from an- tride are fairly stable compared to NaH, ° thraquinone. which decomposes at 345 C. Na2N, K3N etc., are not obtained pure and decompose alkali /al-kă-lÿ/ A water-soluble strong below room temperature. base. Strictly the term refers to the hydrox- The oxides also display the trend in ides of the alkali metals (group 1) only, but properties as lithium forms M2O with only in common usage it refers to any soluble traces of M2O2, sodium forms M2O2 and base. Thus borax solution may be de- at high temperatures and pressures MO2, scribed as mildly alkaline. potassium, rubidium, and cesium form M2O2 if oxygen is restricted but MO2 if alkali metals (group 1 elements)A burnt in air. Hydrolysis of the oxides or di- group of soft reactive metals, each repre- rect reaction of the metal with water leads senting the start of a new period in the pe- to the formation of the hydroxide ion. riodic table and having an electronic Salts of the bases MOH are known for configuration consisting of a rare-gas all acids and these are generally white crys- structure plus one outer electron. The al- talline solids. The ions M+ are hydrated in kali metals are lithium (Li), sodium (Na), water and remain unchanged in most reac- potassium (K), rubidium (Rb), cesium (Cs), tions of alkali metal salts. and francium (Fr). They formerly were Because of the ease of formation of the classified in subgroup IA of the periodic ions M+ there are very few coordination + table. compounds of the type MLn apart from The elements all easily form positive solvated species of very low correlation ions M+ and consequently are highly reac- times. The group 1 elements form a variety tive (particularly with any substrate that is of organometallic compounds; the bonding

9 alkalimetry in lithium alkyls and aryls is essentially co- ble, and BaSO4 very insoluble). The trend valent but the heavier elements form ionic to increasing metallic character is also compounds. Organo-alkali metal com- shown by the increase in thermal stabilities pounds – particularly the lithium com- of the carbonates and nitrates with increas- pounds – are widely used in synthetic ing relative atomic mass. organic chemistry. The elements all burn in air (beryllium Francium is formed only by radioactive must be finely powdered) to give the oxide decay and in nuclear reactions; all the iso- MO (covalent in the case of beryllium) and topes of francium have short half-lives, the for barium the peroxide, BaO2 in addition longest of which is 21 minutes (francium- to BaO. The heavier oxides, CaO, SrO, and 223). The few chemical studies which have BaO, react with water to form hydroxides, been carried out indicate that it would have M(OH)2; magnesium oxide reacts only at similar properties to those of the other al- high temperatures and beryllium oxide not kali metals. at all. The metals Ca, Sr, and Ba all react readily with water to give the hydroxide: → 2+ – alkalimetry /al-kă-lim-ĕ-tree/ See acidime- M + 2H2O M + 2OH + H2 try. In contrast, magnesium requires dilute acids in order to react (to the salt plus hy- alkaline-earth metals (group 2 ele- drogen), and beryllium is resistant to acid ments) A group of moderately reactive attack. A similar trend is seen in the direct metals, harder and less volatile than the al- reaction of hydrogen: under mild condi- kali metals. They were formerly classified tions calcium, strontium, and barium give in subgroup IIA of the periodic table. The ionic hydrides, high pressures are required term alkaline earth strictly refers to the ox- to form magnesium hydride, and beryllium ides, but is often used loosely for the ele- hydride can not be prepared by direct com- ments themselves. The electronic bination. configurations are all those of a rare-gas Because of its higher polarizing power, structure with an additional two electrons beryllium forms a range of complexes in in the outer s orbital. The elements are which the beryllium atom should be beryllium (Be), magnesium (Mg), calcium treated as an electron acceptor (i.e. the va- (Ca), strontium (Sr), barium (Ba), and ra- cant p orbitals are being used). Complexes dium (Ra). The group shows an increasing such as etherates, acetylethanoates, and the 2– tendency to ionize to the divalent state tetrafluoride (BeF4 ) are formed, all of M2+. The first member, beryllium has a which are tetrahedral. In contrast Mg2+, much higher ionization potential than the Ca2+, Sr2+, and Ba2+ have poor acceptor others and the smallest atomic radius. properties and form only weak complexes, Thus it has a high charge/size ratio and even with donors such as ammonia or edta. consequently the bonding in beryllium Magnesium forms Grignard reagents compounds is largely covalent. The chem- (RMgX), which are important in organic istry of the heavier members of the group is synthesis, and related compounds largely that of divalent ions. R2Mg.MgX2 and R2Mg are known. The The group displays a typical trend to- few organic compounds of Ca, Sr, and Ba wards metallic character as the group is are ionic. All isotopes of radium are ra- descended. For example, beryllium hy- dioactive and radium was once widely used droxide is amphoteric; magnesium hydrox- for radiotherapy. The half-life of 226Ra ide is almost insoluble in water and is (formed by decay of 238U) is 1600 years. slightly basic; calcium hydroxide is sparingly soluble and distinctly basic; and alkaloid /al-kă-loid/ One of a group of strontium and barium hydroxides are in- natural organic compounds found in creasingly soluble in water and strongly plants. They contain oxygen and nitrogen basic. The group also displays a smooth atoms; most are poisonous. However, they trend in the solubilities of the sulfates include a number of important drugs with (MgSO4 is soluble, CaSO4 sparingly solu- characteristic physiological effects, e.g. 10 alkylbenzene

→ morphine, codeine, caffeine, cocaine, and RCH2CH2Br + KOH KBr + H2O + nicotine. RCH:CH2 2. The dehydration of an alcohol by pass- alkane /al-kayn/ A type of hydrocarbon ing the vapor over hot pumice (400°C): → with general formula CnH2n+2. Alkanes are RCH2CH2OH RCH:CH2 + H2O saturated compounds, containing no dou- The reactions of alkenes include: ble or triple bonds. Methane (CH4) and 1. Hydrogenation using a catalyst (usually ethane (C H ) are typical examples. The nickel at about 150°C): 2 6 → alkanes are fairly unreactive (their former RCH:CH2 + H2 RCH2CH3 name, the paraffins, means ‘small affin- 2. Addition reactions with halogen acids to ity’). In ultraviolet radiation they react give haloalkanes: → with chlorine to give a mixture of substitu- RCH:CH2 + HX RCH2CH2X tion products. There are a number of ways The addition follows Markovnikoff’s of preparing alkanes: rule. 1. From a sodium salt of a carboxylic acid 3. Addition reactions with halogens, e.g. → treated with soda lime: RCH:CH2 + Br2 RCHBrCH2Br – + → 4. Hydration using concentrated sulfuric RCOO Na + NaOH RH + Na2CO3 2. By reduction of a haloalkane with acid, followed by dilution and warming: → nascent hydrogen from the action of RCH:CH2 + H2O RCH(OH)CH3 ethanol on a zinc–copper couple: 5. Oxidation by cold potassium perman- → ganate solutions to give diols: RX + 2[H] RH + HX → 3. By the Wurtz reaction – i.e. sodium in RCH:CH2 + H2O + [O] RCH(OH)CH OH dry ether on a haloalkane: 2 Ethene can be oxidized in air using a 2RX + 2Na → 2NaX + RR silver catalyst to the cyclic compound 4. By the Kolbé electrolytic method: epoxyethane (C H O). RCOO– → RR 2 4 6. Polymerization to polyethene (by the 5. By refluxing a haloalkane with magne- Ziegler or Phillips process). sium in dry ether to form a Grignard See also oxo process; ozonolysis. reagent: RI + Mg → RMgI alkoxide /al-koks-ÿd/ An organic com- 5. With acid this gives the alkane: – → pound containing an ion of the type RO , RMgI + H RH where R is an alkyl group. Alkoxides are The main source of lower molecular made by the reaction of metallic sodium on weight alkanes is natural gas (for methane) – + an alcohol. Sodium ethoxide (C2H5O Na ) and crude oil. is a typical example. alkene /al-keen/ A type of hydrocarbon alkoxyalkane /al-koks-ee-al-kayn/ (Di- with the general formula CnH2n. The ethyl ether.) See ether. alkenes (formerly called olefins) are unsaturated compounds containing double car- alkylbenzene /al-kăl-ben-zeen/ A type bon–carbon bonds. They can be obtained of organic hydrocarbon containing one or from crude oil by cracking alkanes. Impor- more alkyl groups substituted onto a ben- tant examples are ethene (C H ) and 2 4 zene ring. Methylbenzene (C6H5CH3) and propene (C3H6), both of which are used in 1,3-dimethylbenzene are simple examples. plastics production and as starting materi- Alkylbenzenes can be made by a Friedel- als for the manufacture of many other or- Crafts reaction or by the Fittig reaction. In- ganic chemicals. dustrially, large quantities of methyl- The methods of synthesizing alkenes benzene are made by the hydroforming of are: crude oil. 1. The elimination of HBr from a Substitution of alkylbenzenes can occur haloalkane using an alcoholic solution at the benzene ring. The alkyl group directs of potassium hydroxide: the substituent into the 2- or 4-position.

11 alkyl group

Substitution of hydrogen atoms on the 6. Ethyne forms unstable dicarbides alkyl group can also occur. (acetylides) with ammoniacal solutions of copper(I) and silver(I) chlorides. alkyl group /al-kăl/ A group obtained by removing a hydrogen atom from an allotropy /ă-lot-rŏ-pee/ The ability of alkane or other aliphatic hydrocarbon. certain elements to exist in more than one physical form. Carbon, sulfur, and phos- alkyl halide See haloalkane. phorus are the most common examples. Allotropy is more common in groups 14, alkyl sulfide A thioether with the gen- 15, and 16 of the periodic table than in eral formula RSR′, where R and R′ are other groups. See also enantiotropy; alkyl groups. monotropy. alkyne /al-kÿn/ A type of hydrocarbon alloy A mixture of two or more metals with the general formula CnH2n–2. The (e.g. bronze or brass) or a metal with small alkynes are unsaturated compounds con- amounts of non-metals (e.g. steel). Alloys taining triple carbon–carbon bonds. The may be completely homogeneous mixtures simplest member of the series is ethyne or may contain small particles of one phase (C2H2), which can be prepared by the ac- in the other phase. tion of water on calcium dicarbide. → CaC2 + 2H2O Ca(OH)2 + C2H2 allyl group /al-ăl/ See propenyl group. The alkynes were formerly called the acetylenes. Alnico /al-mă-koh/ (Trademark) Any of In general, alkynes can be made by the a group of very hard brittle alloys used to cracking of alkanes or by the action of a make powerful permanent magnets. They hot alcoholic solution of potassium hy- contain nickel, aluminum, cobalt, and cop- droxide on a dibromoalkane, for example: per in various proportions. Iron, titanium, → BrCH2CH2Br + KOH KBr + and niobium can also be present. They CH2:CHBr + H2O have a high remanence and coercive force. → CH2:CHBr + KOH CHCH + KBr + 2+ H2O alpha particle A He ion emitted with The main reactions of the alkynes are: high kinetic energy by a radioactive sub- 1. Hydrogenation with a catalyst (usually stance. Alpha particles are used to cause nickel at about 150°C): nuclear disintegration reactions. → C2H2 + H2 C2H4 → C2H4 + H2 C2H6 alternating copolymer See polymer- 2. Addition reactions with halogen acids: ization. → C2H2 + HI H2C:CHI → H2C:CHI + HI CH3CHI2 alum A type of double salt. Alums are 3. Addition of halogens; for example, with double sulfates obtained by crystallizing bromine in tetrachloromethane: mixtures in the correct proportions. They → C2H2 + Br2 BrHC:CHBr have the general formula: → ′ BrHC:CHBr + Br2 Br2HCCHBr2 M2SO4.M 2(SO4)3.24H2O 4. With dilute sulfuric acid at 60–80°C and Where M is a univalent metal or ion, mercury(II) catalyst, ethyne forms and M′ is a trivalent metal. Thus, alu- ethanal (acetaldehyde): minum potassium sulfate (called potash → C2H2 + H2O H2C:C(OH)H alum, or simply alum) is This enol form converts to the alde- K2SO4.Al2(SO4)3.24H2O hyde: Aluminum ammonium sulfate (called CH3COH ammonium alum) is 5. Ethyne polymerizes if passed through a (NH4)2SO4.Al2(SO4)3.24H2O hot tube to produce some benzene: The name ‘alum’ originally came from → 3+ 3C2H2 C6H6 the presence of Al as the trivalent ion, but 12 aluminum chloride is also applied to other salts containing The reaction of aluminum metal with trivalent ions, thus, Chromium(III) potas- oxygen is very exothermic but at ordinary sium sulfate (chrome alum) is temperatures an impervious film of the K2SO4.Cr2(SO4)3.24H2O oxide protects the bulk metal from further attack. This oxide film also protects alu- alumina See aluminum oxide. minum from oxidizing acids. There is only one oxide, Al2O3 (alumina), but a variety aluminate See aluminum hydroxide. of polymorphs and hydrates are known. It is relatively inert and has a high melting aluminosilicate /ă-loo-mă-noh-sil-ă-kayt/ point, and for this reason is widely used as See silicates. a furnace lining and for general refractory brick. Aluminum metal will react with al- aluminum A soft moderately reactive kalis releasing hydrogen and producing ini- – metal; the second element in group 3 of the tially Al(OH)3 then Al(OH)4 . periodic table. It was formerly classified in Aluminum reacts readily with the halo- subgroup IIIA. Aluminum has the elec- gens; in the case of chlorine thin sheets will tronic structure of neon plus three addi- burst into flame. The fluoride has a high tional outer electrons. There are numerous melting point (1290°C) and is ionic. The minerals of aluminum; it is the most com- other halides are dimers in the vapor phase mon metallic element in the Earth’s crust (two halogen bridges). Aluminum also (8.1% by weight) and the third in order of forms a sulfide (Al2S3), nitride (AlN), and abundance. Commercially important min- carbide (Al4C), the latter two at extremely erals are bauxite (hydrated Al2O3), corun- high temperatures. dum (anhydrous Al2O3), cryolite Because of aluminum’s ability to ex- (Na3AlF6), and clays and mica (aluminosil- pand its coordination number and ten- icates). dency towards covalence it forms a variety 2– – The metal is produced on a massive of complexes such as AlF6 and AlCl4 . A scale by the Hall–Heroult method in which number of very reactive aluminum alkyls alumina, a non-electrolyte, is dissolved in are also known, some of which are impor- molten cryolite and electrolyzed. The tant as polymerization catalysts. bauxite contains iron, which would conta- Symbol: Al; m.p. 660.37°C; b.p. minate the product, so the bauxite is dis- 2470°C; r.d. 2.698 (20°C); p.n. 13; r.a.m. solved in hot alkali, the iron oxide is 26.981539. removed by filtration, and the pure alumina then precipitated by acidification. aluminum acetate See aluminum Molten aluminum is tapped off from the ethanoate. base of the cell and oxygen evolved at the anode. The aluminum atom is much bigger aluminum bromide (AlBr3) A white than boron (the first member of group 3) solid soluble in water and many organic and its ionization potential is not particu- solvents. larly high. Consequently aluminum forms 3+ positive ions Al . However, it also has aluminum chloride (AlCl3) A white co- non-metallic chemical properties. Thus, it valent solid that fumes in moist air: → is amphoteric and also has a number of co- AlCl3 + 3H2O Al(OH)3 + 3HCl valently bonded compounds. It is prepared by heating aluminum in dry Unlike boron, aluminum does not form chlorine or dry hydrogen chloride. Vapor- a vast range of hydrides – AlH3 and Al2H6 density measurements show that its struc- may exist at low pressures, and the only ture is a dimer; it consists of Al2Cl6 stable hydride, (AlH3)n, must be prepared molecules in the vapor. The AlCl3 structure by reduction of aluminum trichloride. The would be electron-deficient. Aluminum – ion AlH4 is widely used in the form of chloride is used in Friedel–Crafts reactions LiAlH4 as a vigorous reducing agent. in organic preparations. 13 aluminum ethanoate aluminum ethanoate (aluminum acetate; aluminum, as an abrasive (corundum), in Al(OOCCH3)3) A white solid soluble in furnace linings (because of its refractory water. It is usually obtained as the dibasic properties), and as a catalyst (e.g. in the de- salt, basic aluminum ethanoate, hydration of alcohols). Al(OH)(CH3COO)2. It is prepared by dissolving aluminum hydroxide in ethanoic aluminum potassium sulfate (potash acid and is used extensively as a mordant in alum; Al2(SO4)3.K2SO4.24H2O) A white dyeing and as a size for paper and card- solid, soluble in water but insoluble in al- board products. The solution is hydrolyzed cohol, prepared by mixing equimolecular and contains various complex aluminum- quantities of solutions of ammonium and hydroxyl species and colloidal aluminum aluminum sulfate followed by crystalliza- hydroxide. tion. It is used as a mordant for dyes, as a waterproofing agent, and as a tanning ad- aluminum fluoride (AlF3) A white ditive. crystalline solid that is slightly soluble in water but insoluble in most organic sol- aluminum sulfate (Al2(SO4)3.18H2O) vents. Its primary use is as an additive to A white crystalline solid. It is used as a size the cryolite (Na3AlF6) electrolyte in the for paper, a precipitating agent in sewage production of aluminum. treatment, a foaming agent in fire control, and as a fireproofing agent. Its solutions aluminum hydroxide (Al(OH)3)A are acidic by hydrolysis, containing such 2+ white powder prepared as a colorless species as Al(H2O)5(OH) . gelatinous precipitate by adding ammonia solution or a small amount of sodium hy- aluminum trimethyl /trÿ-meth-ăl/ See droxide solution to a solution of an alu- trimethylaluminum. minum salt. It is an amphoteric hydroxide and is used as a foaming agent in fire ex- amalgam /ă-mal-găm/ An alloy of mer- tinguishers and as a mordant in dyeing. cury with one or more other metals. Amal- Its amphoteric nature causes it to dis- gams may be liquid or solid. An amalgam solve in excess sodium hydroxide solution of sodium (Na/Hg) with water is used as a to form the aluminate ion (systematic name source of nascent hydrogen. tetrahydroxoaluminate(III)): – → – Al(OH)3 + OH Al(OH)4 + H2O amatol /am-ă-tol, -tohl/ A high explo- When precipitating from solution, alu- sive that consists of a mixture of ammo- minum hydroxide readily absorbs colored nium nitrate and TNT (trinitrotoluene). matter from dyes to form lakes. ambidentate See isomerism. aluminum nitrate (Al(NO3)3.9H2O) A hydrated white crystalline solid prepared americium /am-ĕ-rish-ee-ŭm/ A highly by dissolving freshly prepared aluminum toxic radioactive silvery element of the hydroxide in nitric acid. It cannot be pre- actinoid series of metals. A transuranic ele- pared by the action of dilute nitric acid on ment, it is not found naturally on Earth but aluminum since the metal is rendered pas- is synthesized from plutonium. The ele- sive by a thin surface layer of oxide. ment can be obtained by reducing the trifluoride with barium metal. It reacts with 241 aluminum oxide (alumina; Al2O3)A oxygen, steam, and acids. Am has been white powder that is almost insoluble in used in gamma-ray radiography. water. Because of its amphoteric nature it Symbol: Am; m.p. 1172°C; b.p. will react with both acids and alkalis. Alu- 2607°C; r.d. 13.67 (20°C); p.n. 95; most minum oxide occurs naturally as bauxite, stable isotope 243Am (half-life 7.37 × 103 corundum, and white sapphire; it is manu- years). factured by heating aluminum hydroxide. It is used in the extraction by electrolysis of amethyst A purple form of the mineral

14 amine salt

H quartz (silicon(IV) oxide, SiO2) used as a semiprecious gemstone. The color comes C H N from impurities such as oxides of iron. 2 5 H amide /am-ÿd, -id/ 1. A type of organic compound of general formulae RCONH2 primary (ethylamine) (primary), (RCO)2NH (secondary), and (RCO)3N (tertiary). Amides are white, crystalline solids and are basic in nature, some being soluble in water. Amides can be formed by reaction of ammonia with acid C2H5 chlorides or anhydrides: → (RCO)2O + 2NH3 RCONH2 + C H N – + 2 5 RCOO NH4 Reactions of amides include: H 1. Reaction with hot acids to give carboxylic acids: secondary (diethylamine) → RCONH2 + HCl + H2O RCOOH + NH4Cl 2. 2. Reaction with nitrous acid to give carboxylic acids and nitrogen: → RCONH2 + HNO2 RCOOH + N2 + C2H5 H2O 3. 3. Dehydration by phosphorus(V) oxide to C2H5 N give a nitrile: → C2H5 RCONH2 – H2O RCN See also Hofmann degradation. – tertiary (triethylamine) 2. An inorganic salt containing the NH2 ion. They are formed by the reaction of Amines ammonia with certain metals (such as sodium and potassium). See sodamide. + nium ion, R3NH . All three classes, plus a amination /am-ă-nay-shŏn/ The intro- quaternium salt, can be produced by the duction of an amino group (–NH2) into an Hofmann reaction (which occurs in a organic compound. An example is the con- sealed vessel at 100°C): → + – version of an aldehyde or ketone into an RX + NH3 RNH3 X + – ˆ amide by reaction with hydrogen and am- RNH3 X + NH3 RNH2 + NH4X → + – monia in the presence of a catalyst: RNH2 + RX R2NH2 X → + – ˆ RCHO + NH3 + N2 RCH2NH2 + R2NH2 X + NH3 R2NH + NH4X → + – H2O R2NH + RX R3NH X + – ˆ R3NH X + NH3 R3N + NH4X → + – amine /ă-meen, am-in/ A compound con- R3N + RX R4N X taining a nitrogen atom bound to hydrogen Reactions of amines include: atoms or hydrocarbon groups. They have 1. Reaction with acids to form salts: → + – the general formula R3N, where R can be R3N + HX R3NH X hydrogen or an alkyl or aryl group. Amines 2. Reaction with acid chlorides to give N- can be prepared by reduction of amides or substituted acid amides (primary and nitro compounds. secondary amines only): ′ → ′ An amine is classified according to the RNH2 + R COCl R CONHR + HX number of organic groups bonded to the nitrogen atom: one, primary; two, sec- amine salt A salt similar to an ammo- ondary; three, tertiary. Since amines are nium salt, but with organic groups at- basic in nature they can form the quater- tached to the nitrogen atom. For example,

15 amino acids triethylamine ((C2H5)3N) will react with amino acids should be present in sufficient hydrogen chloride to give triethylammo- quantities. In humans, twelve of the twenty nium chloride: amino acids can be synthesized by the body → + – (C2H5)3N + HCl (C2H3)3NH Cl itself. Since these are not required in the Sometimes amine salts are named using the diet they are known as nonessential amino suffix ‘-ium’. For instance, aniline acids. The remaining eight cannot be syn- (C6H5NH2) forms anilinium chloride thesized by the body and have to be sup- + – C6H5NH3 Cl . Often insoluble alkaloids plied in the diet. They are known as are used in medicine in the form of their essential amino acids. amine salt (sometimes referred to as the The amino acids that occur in proteins ‘hydrochloride’). all have the –NH2 group and the –COOH It is also possible for amine salts of this group attached to the same carbon atom. type to have four groups on the nitrogen They are thus alpha amino acids, the car- atom. For example, with chloroethane, bon atom being the alpha carbon. They tetraethylammonium chloride can be have complex formulae and are usually reformed: ferred to by their common names, rather → + – (C2H5)3N + C2H5Cl (C2H5)4N Cl than systematic names: alanine CH CH(NH )COOH amino acids /ă-mee-noh, am-ă-/ Deriva- 3 2 arginine NH2C(NH)NH(CH2)3CH(NH2)- tives of carboxylic acids in which a hydro- COOH gen atom in an aliphatic acid has been asparagine NH2COCH2CH(NH2)COOH replaced by an amino group. Thus, from aspartic acid ethanoic acid, the amino acid 2- COOHCH CH(NH )COOH aminoethanoic acid (glycine) is formed. All 2 2 cysteine SHCH CH(NH )COOH are white, crystalline, soluble in water (but 2 2 cystine [HOOCCH(NH )CH S] not in alcohol), and with the sole exception 2 2 2 glutamic acid COOH(CH ) CH(NH )- of the simplest member, all are optically ac- 2 2 2 COOH tive. glutamine NH CH(CH ) (CONH )- In the body the various proteins are as- 2 2 2 2 COOH sembled from the necessary amino acids glycine CH (NH )COOH and it is important therefore that all the 2 2 histidine C3H3N2CH2CH(NH2)COOH isoleucine (CH3)CH2CH(CH3)CH(NH2)- COOH H O leucine (CH3)2CHCH2CH(NH2)COOH lysine NH2(CH2)4CH(NH2)COOH methionine CH3S(CH2)2CH(NH2)COOH R C C phenylalanine C6H5CH2CH(NH2)COOH proline NH(CH2)3CHCOOH serine CH2OHCH(NH2)COOH NH2 O H threonine CH3CHOHCH(NH2)- un-ionized COOH tryptophan C6H4NHC2HCH2CH(NH2)- COOH H O tyrosine C6H4OHCH2CH(NH2)COOH valine (CH3)2CHCH(NH2)COOH Note that proline is in fact a cyclic R C C imino acid, with the nitrogen atom bonded to the alpha carbon. + See also optical activity. NH3 O zwitterion aminobenzene /ă-mee-noh-ben-zeen, am- Amino acid ă-/ See aniline.

16 ammonium hydroxide aminoethane /a-mee-noh-eth-ayn, am-ă-/ as the liquid, compressed in cylinders (‘an- See ethylamine. hydrous ammonia’), or as aqueous solutions of various strengths. See also amino group The group –NH2. ammonium hydroxide. aminotoluine /ă-mee-noh-tol-yoo-een, ammoniacal /am-ŏ-nÿ-ă-kăl/ Describ- am-ă-/ See toluidine. ing a solution in aqueous ammonia. ammine /am-een, ă-meen/ A complex in ammonia-soda process See Solvay which ammonia molecules are coordinated process. 2+ to a metal ion; e.g. [Cu(NH3)4] . ammonium alum See alum. ammonia /ă-moh-nee-ă/ (NH3) A colorless gas with a characteristic pungent odor. ammonium carbonate (sal volatile; On cooling and compression it forms a col- (NH4)2CO3) A white solid that crystal- orless liquid, which becomes a white solid lizes as plates or prisms. It is very soluble in on further cooling. Ammonia is very solu- water and readily decomposes on heating ble in water (a saturated solution at 0°C to ammonia, carbon dioxide, and water. contains 36.9% of ammonia): the aqueous The white solid sold commercially as am- solution is alkaline and contains a propor- monium carbonate is actually a double salt tion of free ammonia. Ammonia is also sol- of both ammonium hydrogencarbonate uble in ethanol. It occurs naturally to a (NH4HCO3) and ammonium small extent in the atmosphere, and is usu- aminomethanoate (NH2CO2NH4). This ally produced in the laboratory by heating salt is manufactured from ammonium an ammonium salt with a strong alkali. chloride and calcium carbonate. It decom- Ammonia is synthesized industrially from poses on exposure to air into ammonium hydrogen and atmospheric nitrogen by the hydrogencarbonate and ammonia, and it Haber process. reacts with ammonia to give the true am- The compound does not burn readily in monium carbonate. Commercial ammo- air but ignites, giving a yellowish-brown nium carbonate is used in baking powders, flame, in oxygen. It will react with atmos- smelling salts, and in the dyeing and wool- pheric oxygen in the presence of platinum scouring industries. or a heavy metal catalyst – a reaction used as the basis of the commercial manufacture ammonium chloride (sal ammoniac; of nitric acid, which involves the oxidation NH4Cl) A white crystalline solid with a of ammonia to nitrogen monoxide and characteristic saline taste. It is very soluble then to nitrogen dioxide. Ammonia coordi- in water (37 g per 100 g of water at 20°C). nates readily to form ammines and reacts Ammonium chloride can be manufactured with sodium or potassium to form inor- by the action of ammonia on hydrochloric ganic amides and with acids to form am- acid. It sublimes on heating because of the monium salts; for example, it reacts with equilibrium: ˆ hydrogen chloride to form ammonium NH4Cl(s) NH3(g) + HCl(g) chloride: Ammonium chloride is used in galva- → NH3(g) + HCl(g) NH4Cl(g) nizing, as a flux for soldering, in dyeing Ammonia is also used commercially in and calico printing, and in the manufacture the manufacture of fertilizers, mainly am- of Leclanché and ‘dry’ cells. monium nitrate, urea, and ammonium sulfate. It is used to a smaller extent in the ammonium hydroxide (ammonia solu- refrigeration industry. Liquid ammonia is tion; NH4OH) An alkali that is formed an excellent solvent for certain substances, when ammonia dissolves in water. It prob- which ionize in the solutions to give ionic ably contains hydrated ammonia mol- + – reactions similar to those occurring in ecules as well as some NH4 and OH ions. aqueous solutions. Ammonia is marketed A saturated aqueous solution of ammonia

17 ammonium ion has a relative density of 0.88 g cm–3, and is amount of substance Symbol: n A known as 880 ammonia. Ammonia solu- measure of the number of entities present tion is a useful reagent and cleansing agent. in a substance. See mole.

+ ammonium ion The ion NH4 , formed AMP (adenosine monophosphate)A + NUCLEOTIDE consisting of adenine, ribose, by coordination of NH3 to H . See also quaternary ammonium compound. and phosphate. See ATP.

ampere /am-pair/ Symbol: A The SI base ammonium nitrate (NH4NO3) A colorless crystalline solid that is very soluble unit of electric current, defined as the con- in water (871 g per 100 g of water at stant current that, maintained in two 100°C). It is usually manufactured by the straight parallel infinite conductors of negligible circular cross section placed one action of ammonia on nitric acid. It is used meter apart in vacuum, would produce a in the manufacture of explosives and, be- force between the conductors of 2 × 10–7 cause of its high nitrogen content, as a fer- newton per meter. The unit is named for tilizer. the French physicist and mathematician André Marie Ampère (1775–1836). ammonium phosphate (triammonium phosphate (V); (NH4)3PO4) A colorless amphiprotic /am-fă-proh-tik/ See sol- crystalline salt made from ammonia and vent. phosphoric(V) acid, used as a fertilizer to add both nitrogen and phosphorus to the ampholyte ion /am-fŏ-lÿt/ See zwitte- soil. rion. ammonium sulfate ((NH4)2SO4) A col- amphoteric /am-fŏ-te-rik/ A material orless crystalline solid that is soluble in that can display both acidic and basic water. When heated carefully it gives am- properties. The term is most commonly ap- monium hydrogensulfate, which on plied to the oxides and hydroxides of met- stronger heating yields nitrogen, ammonia, als that can form both cations and complex sulfur(IV) oxide (sulfur dioxide), and anions. For example, zinc oxide dissolves water. Ammonium sulfate is manufactured in acids to form zinc salts and also dis- by the action of ammonia on sulfuric acid. solves in alkalis to form zincates, 2– It is the most important ammonium salt be- [Zn(OH)4] . cause of its widespread use as a fertilizer. Its only drawback as a fertilizer is that it amu /ay-em-yoo/ See atomic mass unit. tends to leave an acidic residue in the soil. amyl group /am-ăl/ See pentyl group. amorphous /ă-mor-fŭs/ Describing a amyl nitrite (C H ONO) A pale solid substance that has no ‘long-range’ 5 11 brown volatile liquid organic compound; a regular arrangement of atoms; i.e. is not nitrous acid ester of 3-methylbutanol (iso- crystalline. Amorphous materials can con- amyl alcohol). It is used in medicine as an sist of minute particles that possess order inhalant to dilate the blood vessels (and over a very short distance. Glasses are also thereby prevent pain) in patients with amorphous; the atoms in the solid have a angina pectoris. random arrangement. X-ray analysis has shown that many substances that were amylopectin /am-ă-lo-pek-tin/ The water- once described as amorphous are com- insoluble fraction of STARCH. posed of very small crystals. For example, charcoal, coke, and soot (all forms of car- amylose /am-ă-lohs/ A polymer of GLU- bon) are made up of small graphite-like COSE, a polysaccharide sugar that is found crystals. in starch.

18 aniline anabolism /ă-nab-ŏ-liz-ăm/ All the ångstrom /ang-strŏm/ Symbol: Å A unit metabolic reactions that synthesize com- of length defined as 10–10 meter. The plex molecules from more simple mole- ångstrom is sometimes still used for ex- cules. See also metabolism. pressing wavelengths of light or ultraviolet radiation or for the sizes of molecules, al- anaerobic /an-air-oh-bik/ Describing a though the nanometer is preferred. The biochemical process that takes place in the unit is named for the Swedish physicist An- absence of free oxygen. Compare aerobic. ders Jonas Ångstrom (1814–74). analysis The process of determining the anhydride /an-hÿ-drÿd/ A compound constituents or components of a sample. formed by removing water from an acid or, There are two broad major classes of less commonly, a base. Many non-metal analysis, qualitative analysis – essentially oxides are anhydrides of acids: for example answering the question ‘what is it?’ – and CO2 is the anhydride of H2CO3 and SO3 is quantitative analysis – answering the ques- the anhydride of H2SO4. Organic anhy- tion ‘how much of such and such a compo- drides are formed by removing H2O from nent is present?’ There is a vast number of two carboxylic-acid groups, giving com- analytical methods which can be applied, pounds with the functional group depending on the nature of the sample and –CO.O.CO–. These form a class of organic the purpose of the analysis. These include compounds called ACID ANHYDRIDES (or gravimetric, volumetric, and systematic acyl anhydrides). qualitative analysis (classical wet methods); and instrumental methods, such as anhydrite /an-hÿ-drÿt/ See calcium sul- chromatographic, spectroscopic, nuclear, fate. fluorescence, and polarographic techniques. anhydrous /an-hÿ-drŭs/ Describing a substance that lacks moisture, or a salt Andrews’ experiment An investigation with no water of crystallization. For exam- (1861) into the relationship between pres- ple, on strong heating, blue crystals of cop- sure and volume for a mass of carbon di- per(II) sulfate pentahydrate, CuSO4.5H2O, oxide at constant temperature. The form white anhydrous copper(II) sulfate, resulting isothermals showed clearly the CuSO4. existence of a critical point and led to greater understanding of the liquefaction aniline /an-ă-lin, -lÿn/ (aminobenzene; of gases. The experiment is named for the phenylamine; C6H5NH2) A colorless oily Irish physical chemist Thomas Andrews substance made by reducing nitrobenzene (1813–1885). (C6H5NO2). Aniline is used for making

H3C H3C OC OC HO O HO OC OC H3C H3C

ethanoic acid ethanoic anhydride

Anhydride

19 anion dyes, pharmaceuticals, and other organic the first annulene larger than benzene. It is compounds. not an AROMATIC COMPOUND because it is not planar and does not obey the Hückel anion /an-ÿ-ŏn, -on/ A negatively rule. C8H8 is called cyclo-octatetrane. charged ion, formed by addition of elec- Higher annulenes are designated by the trons to atoms or molecules. In electrolysis number of carbon atoms in the ring. [10]- anions are attracted to the positive elec- annulene obeys the Hückel rule but is not trode (the anode). Compare cation. aromatic because it is not planar as a result of interactions of the hydrogen atoms in- anionic detergent /an-ÿ-on-ik/ See de- side the ring. There is some evidence that tergent. [18]-annulene, which is a stable red solid, has aromatic properties. anionic resin An ION-EXCHANGE material that can exchange anions, such as Cl– anode /an-ohd/ In electrolysis, the elec- and OH–, for anions in the surrounding trode that is at a positive potential with re- medium. Such resins are used for a wide spect to the cathode. In any electrical range of analytical and purification pur- system, such as a discharge tube or elec- poses. tronic device, the anode is the terminal at They are often produced by addition of which electrons flow out of the system. a quaternary ammonium group + – (–N(CH3)3 ) or a phenolic group (–OH ) anode sludge See electrolytic refining. to a stable polyphenylethene resin. A typical exchange reaction is: anodizing /an-ŏ-dÿz-ing/ An industrial + – ˆ resin–N(CH3)3 Cl + KOH process for protecting aluminum with an + – resin–N(CH3)3 OH + KCl oxide layer formed in an electrolytic cell Anionic resins can be used to separate containing an oxidizing acid (e.g. sulfu- mixtures of halide ions. Such mixtures can ric(VI) acid). The layer of Al2O3 is porous be attached to the resin and recovered sep- and can be colored with certain dyes. arately by elution. anomer /an-ŏ-mer/ Either of two iso- anisotropic /an-ÿ-sŏ-trop-ik/ A term de- meric forms of a cyclic form of a sugar that scriptive of certain substances which have differ in the disposition of the –OH group one or more physical properties that differ on the carbon next to the O atom of the according to direction. Most crystals are ring (the anomeric carbon). Anomers are anisotropic. diastereoisomers. They are designated α– or β– according to whether the –OH is annealing /ă-neel-ing/ A type of heat above or below the ring respectively. treatment applied to metals to change their physical properties. The metal is heated to, anthracene /an-thră-seen/ (C14H10)A and held at, an appropriate temperature white crystalline solid used extensively in before being cooled at a suitable rate to the manufacture of dyes. Anthracene is produce the desired grain structure. An- found in the heavy- and green-oil fractions nealing is most commonly used to remove of crude oil and is obtained by fractional the stresses that have arisen during rolling, crystallization. Its structure is benzene-like, to increase the softness of the metal, and to having three six-membered rings fused to- make it easier to machine. Objects made of glass can also be annealed to remove strains. annulene /an-yŭ-leen/ A ring compound containing alternating double and single C–C bonds. The compound C8H8, having an 8-membered ring of carbon atoms, is Anthracene

20 aprotic gether. The reactions are characteristic of antimony(III) chloride oxide See anti- AROMATIC COMPOUNDS. mony(III) chloride. anthracite /an-thră-sÿt/ The highest antimonyl chloride /an-tă-mŏ-nil, an- grade of coal, with a carbon content of be- tim-ŏ-nil/ See antimony(III) chloride. tween 92% and 98%. It burns with a hot blue flame, gives off little smoke and leaves antimony(III) oxide (antimony trioxide; hardly any ash. Sb2O3) A white insoluble solid. It is an amphoteric oxide with a strong tendency anthraquinone /an-thră-kwi-nohn, an- to act as a base. It can be prepared by direct oxidation by air, oxygen, or steam and thră-kwin-ohn/ (C6H4(CO)2C6H4) A colorless crystalline quinone used in is formed when antimony(III) chloride is producing dyestuffs such as alizarin. hydrolyzed by excess boiling water. antibonding orbital See orbital. antimony(V) oxide (antimony pentoxide; Sb2O5) A yellow solid. It is usually anti-isomer /an-tee-ÿ-sŏ-mer/ See iso- formed by the action of concentrated nitric merism. acid on antimony or by the hydrolysis of antimony(V) chloride. Although an acidic antiknock agent /an-tee-nok/ A sub- oxide, it is only slightly soluble in water. stance added to gasoline to inhibit preignition or ‘knocking’. A common example is antimony pentoxide /pen-toks-ÿd/ See lead tetraethyl. antimony(V) oxide. trÿ-klor-ÿd, -kloh- antimonic /an-tă-mon-ik/ Designating antimony trichloride / rÿd/ See antimony(III) chloride. an antimony(IV) compound. antimony trioxide /trÿ-oks-ÿd/ See an- antimonous /an-tă-moh-nŭs/ Designat- timony(III) oxide. ing an antimony(III) compound. antioxidant /an-tee-oks-ă-dănt/ A sub- antimony /an-tă-moh-nee/ A metalloid stance that inhibits oxidation. Antioxi- element existing in three allotropic forms; dants are added to such products as foods, the most stable is a brittle silvery metal. paints, plastics, and rubber to delay their Antimony belongs to group 15 (formerly oxidation by atmospheric oxygen. Some VB) of the periodic table. It is found in work by forming chelates with metal ions, many minerals, principally stibnite (Sb2S3). thus neutralizing the catalytic effect of the It is used in alloys – small amounts of anti- ions in the oxidation process. Other types mony can harden other metals. It is also remove intermediate oxygen free radicals. used in semiconductor devices. Naturally occurring antioxidants can limit ° Symbol: Sb; m.p. 630.74 C; b.p. tissue or cell damage in the body. These in- ° 1635 C; r.d. 6.691; p.n. 51; r.a.m. 112.74. clude vitamin E and β-carotene. antimony(III) chloride (antimony antiparallel spins /an-tee-pa-ră-lel/ Spins trichloride; SbCl3) A white deliquescent of two neighboring particles in which the solid, formerly known as butter of anti- magnetic moments associated with the spin mony. It is prepared by direct combination are aligned in opposite directions. of antimony and chlorine. It is readily hydrolyzed by cold water to form a white pre- apatite /ap-ă-tÿt/ A naturally occurring cipitate of antimony(III) chloride oxide phosphate of calcium, CaF2.Ca3(PO4)3. (antimonyl chloride, SbOCl):

SbCl3 + H2O = SbOCl + 2HCl aprotic /ă-prot-ik, -proh-tik/ See solvent. 21 aqua fortis aqua fortis /a-kwă for-tis/ An old name they tend to undergo nucleophilic substitu- for nitric acid, HNO3. tion of hydrogen (or other groups) on the ring, and addition reactions only occur aqua regia /ree-jee-ă/ A mixture of con- under special circumstances. centrated nitric acid and three to four parts The explanation of this behavior is that of hydrochloric acid. It dissolves all metals the electrons in the double bonds are delo- including gold, hence the name. The mix- calized over the ring, so that the six bonds ture contains chlorine and NOCl (nitrosyl are actually all identical and intermediate chloride). between single bonds and double bonds. The pi electrons are thus spread in a mole- aqueous /ay-kwee-ŭs, ak-wee-/ Describ- cular orbital above and below the ring. The ing a solution in water. evidence for this delocalization in benzene is that: The bond lengths between carbon aragonite /ă-rag-ŏ-nÿt, a-ră-gŏ-nÿt/An atoms in benzene are all equal and inter- anhydrous mineral form of calcium car- mediate between single and double bond bonate, CaCO3, which occurs associated lengths. Also, if two hydrogen atoms at- with limestone and in some metamorphic tached to adjacent carbon atoms are sub- rocks. It is also the main ingredient of stituted by other groups, the compound pearls. It is not as stable as calcite, into has only one structure. If the bonds were which it may change over time. different two isomers would exist. Benzene has a stabilization energy of 150 kJ mol–1 /ă-reen/ An organic compound arene over the Kekulé structure. containing a benzene ring; i.e. an aromatic The delocalization of the electrons in hydrocarbon or derivative. the pi orbitals of benzene accounts for the properties of benzene and its derivatives, argentic oxide /ar-jen-tik/ See silver(II) which differ from the properties of alkenes oxide. and other aliphatic compounds. The phenomenon is called aromaticity. A defini- argentous oxide /ar-jen-tŭs/ See silver(I) tion of aromaticity is that it occurs in oxide. compounds that obey the Hückel rule: i.e. arginine /ar-jă-nÿn/ See amino acids. that there should be a planar ring with a total of (4n + 2) pi electrons (where n is any argon /ar-gon/ An inert colorless odor- integer). Using this rule as a criterion cer- less monatomic element of the rare-gas tain non-benzene rings show aromaticity. group. It forms 0.93% by volume of air. Such compounds are called nonbenzenoid Argon is used to provide an inert atmos- aromatics. Other compounds that have a phere in electric and fluorescent lights, in ring of atoms with alternate double and welding, and in extracting titanium and sil- single bonds, but do not obey the rule (e.g. icon. The element forms no known com- cyclooctotetraene, which has a non-planar pounds. ring of alternating double and single Symbol: Ar; m.p. –189.37°C; b.p. bonds) are called pseudoaromatics. The –185.86°C; d. 1.784 kg m–3 (0°C); p.n. 18; rule is named for the German chemist Erich r.a.m. 39.95. Armand Arthur Joseph Hückel (1896– 1980). aromatic compound An organic com- Compare aliphatic compound. See also pound containing benzene rings in its resonance. structure. Aromatic compounds, such as benzene, have a planar ring of atoms linked aromaticity /ă-roh-mă-tis-ă-tee/ See by alternate single and double bonds. The aromatic compound. characteristic of aromatic compounds is that their chemical properties are not those Arrhenius equation /ah-ren-ee-ŭs/An expected for an unsaturated compound; equation relating the rate constant of a

22 artificial radioactivity chemical reaction and the temperature at AsCl3) A poisonous oily liquid. It fumes which the reaction is taking place: in moist air due to hydrolysis with water k = Aexp(–Ea/RT) vapor: where A is a constant, k the rate constant, AsCl3 + 3H2O = As2O3 + 6HCl T the thermodynamic temperature in Arsenic(III) chloride is covalent and ex- kelvins, R the gas constant, and Ea the ac- hibits nonmetallic properties. tivation energy of the reaction. Reactions proceed at different rates at arsenic hydride See arsine. different temperatures, i.e. the magnitude of the rate constant is temperature depen- arsenic(III) oxide (white arsenic; arse- dent. The Arrhenius equation is often writ- nious oxide; As2O3) A colorless crys- ten in a logarithmic form, i.e. talline solid that is very poisonous (0.1 g logek = logeA – E/2.3RT would be a lethal dose). Analysis of the This equation enables the activation en- solid and vapor states suggests a dimerized ergy for a reaction to be determined. The structure of As4O6. An amphoteric oxide, equation is named for the Swedish physical arsenic(III) oxide is sparingly soluble in chemist Svante August Arrhenius water, producing an acidic solution. It is (1859–1927). formed when arsenic is burned in air or oxygen. arsenate(III) /ar-sĕ-nayt/ (arsenite)A salt of the hypothetical arsenic(III) acid, arsenic(V) oxide (arsenic oxide; formed by reacting arsenic(III) oxide with As2O5) A white amorphous deliquescent alkalis. Arsenate(III) salts contain the ion solid. It is an acidic oxide prepared by dis- 3– AsO3 . Copper arsenate(III) is used as an solving arsenic(III) oxide in hot concen- insecticide. trated nitric acid, followed by crystallization then heating to 210°C. arsenate(V) A salt of arsenic(V) acid, made by reacting arsenic(III) oxide, As2O3, arsenide /ar-sĕ-nÿd/ A compound of ar- with nitric acid. Arsenate(V) salts contain senic and another metal. For example, with 3– the ion AsO4 . Disodiumhydrogenarsen- iron arsenic forms iron(III) arsenide, ate(V) is used in printing calico. FeAs2, and gallium arsenide, GaAs, is an important semiconductor. arsenic /ar-sĕ-nik, ars-nik; adj. ars-sen- ik/ A toxic metalloid element existing in arsenious chloride /ar-sen-ee-ŭs/ See several allotropic forms; the most stable is arsenic(III) chloride. a brittle gray metal. It belongs to group 15 (formerly VA) of the periodic table. Ar- arsenious oxide See arsenic(III) oxide. senic is found native and in several ores including mispickel (FeSAs), realgar (As4S4), arsenite /ar-sĕ-nÿt/ See arsenate(III). and orpiment (As2S3). The element reacts with hot acids and molten sodium hydrox- arsine /ar-seen, ar-seen, -sin/ (arsenic hy- ide but is unaffected by water and acids dride; AsH3) A poisonous colorless gas and alkalis at normal temperatures. It is with an unpleasant smell. It decomposes to used in semiconductor devices, alloys, and arsenic and hydrogen at 230°C. It is pro- gun shot. Various compounds are used in duced in the analysis for arsenic (Marsh’s medicines and agricultural insecticides and test). poisons. Symbol: As; m.p. 817°C (gray) at 3 artificial radioactivity Radioactivity MPa pressure; sublimes at 616°C (gray); induced by bombarding stable nuclei with r.d. 5.78 (gray at 20°C); p.n. 33; r.a.m. high-energy particles. For example: 27 1 → 24 4 74.92159. 13Al + 0n 11Na + 2He represents the bombardment of aluminum arsenic(III) chloride (arsenious chloride; with neutrons to produce an isotope of

23 aryl group sodium. All the transuranic elements asymmetric atom See chirality; iso- (atomic numbers 93 and above) are artifi- merism; optical activity. cially radioactive since they do not occur in nature. atactic polymer See polymerization. aryl group /a-răl/ An organic group de- atmolysis /at-mol-ă-sis/ The separation rived by removing a hydrogen atom from of gases by using their different rates of dif- an aromatic hydrocarbon or derivative. fusion. asbestos /ass-best-ŏs/ A fibrous variety atmosphere A unit of pressure defined of various rock-forming silicate minerals, as 101 325 pascals (atmospheric pressure). The atmosphere is used in chemistry only such as the amphiboles and chrysotile. It for rough values of pressure; in particular, has many uses that employ its properties of for stating the pressures of high-pressure heat-resistance and chemical inertness. industrial processes. Prolonged exposure to asbestos dust may cause asbestosis – a form of lung cancer. atom The smallest part of an element that can exist as a stable entity. Atoms con- asparagine /ă-spa-ră-jeen, -jin/ See sist of a small dense positively charged nu- amino acids. cleus, made up of neutrons and protons, with electrons in a cloud around this nu- aspartic acid /ă-spar-tik/ See amino cleus. The chemical reactions of an element acids. are determined by the number of electrons (which is equal to the number of protons in aspirator An apparatus for sucking a the nucleus). All atoms of a given element gas or liquid from a vessel or body cavity. have the same number of protons (the proton number). A given element may have aspirin (acetylsalicylic acid; C9H8O4)A two or more isotopes, which differ in the colorless crystalline compound made by number of neutrons in the nucleus. treating salicylic acid with ethanoyl hy- The electrons surrounding the nucleus dride. It is used as an analgesic and an- are grouped into shells – i.e. main orbits tipyretic drug, and small doses are around the nucleus. Within these main or- prescribed for patients at risk of heart at- bits there may be sub-shells. These corre- tack or stroke. It should not be given to spond to atomic orbitals. An electron in an young children. atom is specified by four quantum numbers: association The combination of mole- 1. The principal quantum number (n), cules of a substance with those of another which specifies the main energy levels. n to form more complex species. An example can have values 1, 2, etc. The corresponding shells are denoted by letters K, is a mixture of water and ethanol (which L, M, etc., the K shell (n = 1) being the are termed associated liquids), the mole- nearest to the nucleus. The maximum cules of which combine via hydrogen number of electrons in a given shell is bonding. 2n2. 2. The orbital quantum number (l), which astatine /ass-tă-teen, -tin/ A radioactive specifies the angular momentum. For a element belonging to the halogen group. It given value of n, 1 can have possible val- occurs in minute quantities in uranium ues of n–1, n–2, … 2, 1, 0. For instance, ores. Many short-lived radioisotopes are the M shell (n = 3) has three sub-shells known, all alpha-particle emitters. with different values of l (0, 1, and 2). Symbol: At; m.p. 302°C (est.); b.p. Sub-shells with angular momentum 0, 1, 337°C (est.); p.n. 85; most stable isotope 2, and 3 are designated by letters s, p, d, 210At (half-life 8.1 hours). and f.

24 Aufbau principle

3. The magnetic quantum number (m). atomic heat See Dulong and Petit’s law. This can have values –l, –(l – 1) … 0 … + (l + l), + 1. It determines the orienta- atomicity /at-ŏ-mis-ă-tee/ The number tion of the electron orbital in a magnetic of atoms per molecule of an element. He- field. lium, for example, has an atomicity of one, 4. The spin quantum number (ms), which nitrogen two, and ozone three. specifies the intrinsic angular momentum of the electron. It can have values atomic mass unit (amu; dalton) Symbol: +½ and –½. u A unit of mass used for atoms and mol- Each electron in the atom has four ecules, equal to 1/12 of the mass of an quantum numbers and, according to the atom of carbon-12. It is equal to 1.660 33 Pauli exclusion principle, no two electrons × 10–27 kg. can have the same set of quantum numbers. This explains the electronic structure atomic number See proton number. of atoms. See also Bohr theory. atomic orbital See orbital. atomic absorption spectroscopy (AAS) A technique in chemical analysis in which atomic weight See relative atomic mass a sample is vaporized and an absorption (r.a.m.). spectrum is taken of the vapor. The elements present are identified by their char- ATP (adenosine triphosphate) The uni- acteristic absorption lines. versal energy carrier of living cells. Energy from respiration or, in photosynthesis, atomic emission spectroscopy (AES) from sunlight is used to make ATP from A technique in chemical analysis that ADP. It is then reconverted to ADP in var- involves vaporizing a sample of material ious parts of the cell by enzymes known as at high temperature. Atoms in excited ATPases, the energy released being used to states decay to the ground state, emitting drive three main cellular processes: me- electromagnetic radiation at particular fre- chanical work (muscle contraction and cel- quencies characteristic of that type of lular movement); the active transport of atom. molecules and ions; and the biosynthesis of atomic force microscope (AFM) An biomolecules. It can also be converted to instrument used to investigate surfaces. A light, electricity, and heat. small probe consisting of a very small chip ATP is a NUCLEOTIDE consisting of ade- of diamond is held just above a surface of nine and ribose with three phosphate a sample by a spring-loaded cantilever. As groups attached. Hydrolysis of the termi- the probe is slowly moved over the surface nal phosphate bond releases energy –1 the force between the surface and the tip is (30.6 kJ mol ) and is coupled to an en- measured and the probe is automatically ergy-requiring process. Further hydrolysis raised and lowered to keep this force con- of ADP to AMP sometimes occurs, releas- stant. Scanning the surface in this way ening more energy. ables a contour map of the surface to be –18 generated with the help of a computer. An atto- Symbol: a A prefix denoting 10 . –18 atomic force microscope closely resembles For example, 1 attometer (am) = 10 a SCANNING TUNNELLING MICROSCOPE (STM) meter (m). in some ways, although it uses forces rather than electrical signals to investigate the Aufbau principle /owf-bow/ A principle surface. Like a STM, it can resolve individ- that governs the order in which the atomic ual molecules. Unlike a STM, it can be used orbitals are filled in elements of successive to investigate nonconducting materials, a proton number; i.e. a statement of the feature that is useful in investigating bio- order of increasing energy. The order is as logical samples. follows:

25 Auger effect

1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, autoclave /aw-tŏ-klayv/ An apparatus 4d10, 5p6, 6s2, 4f14, 5d10, 6p6, 7s2, 5f14, consisting of an airtight container whose 6d10 contents are heated by high-pressure (the superscript indicates the maximum steam; the contents may also be agitated. number of electrons for each level). Autoclaves are used for reactions between Note gases under pressure in industrial process- 1. Hund’s rule of maximum multiplicity ing and for sterilizing objects. applies; i.e. degenerate orbitals are occupied singly before spin pairing occurs. autoionization /aw-toh-ÿ-ŏ-ni-zay- 2. the unexpected position of the d-levels, shŏn/ The spontaneous ionization of ex- which give rise to the first, second, and cited atoms, ions or molecules as in the third transition series. Auger effect 3. the unusual position of the f-levels, giving rise to the lanthanoids and actinoids. Avogadro constant /ah-vŏ-gah-droh/ ‘Aufbau’ is a German word meaning (Avogrado’s number) Symbol: NA The ‘building up’. number of particles in one mole of a substance. Its value is 6.022 52 × 1023 mol–1. Auger effect /oh-zhay/ An effect in The constant is named for the Italian physi- which an excited ion decays by emission of cist and chemist Lorenzo Romano Amedeo an electron (rather than a photon). For ex- Carlo Avogadro, Count of Quaregna and ample, if a substance is bombarded by Cerreto (1776–1856). high-energy electrons or gamma rays, an Avogadro’s law The principle that electron from an inner shell may be ejected. equal volumes of all gases at the same tem- The result is a positive ion in an excited perature and pressure contain equal num- state. This ion will decay to its ground state bers of molecules. It is often called by a transition of an outer electron to an Avogadro’s hypothesis. It is strictly true inner shell. The energy released in the tran- only for ideal gases. sition may result in the emission of a photon in the x-ray region of the Avogadro’s number See Avogadro electromagnetic spectrum (this is x-ray flu- constant. orescence). Alternatively, the energy may be released in the form of a second electron azeotrope /ă-zee-ŏ-trop-ik/ (azeotropic ejected from the atom to give a doubly mixture) A mixture of liquids for which charged ion. The emitted electron (known the vapor phase has the same composition as an Auger electron) has a characteristic as the liquid phase. It therefore boils with- energy corresponding to the difference in out change in composition and conse- energy levels in the ion. The Auger effect is quently without progressive change in a form of autoionization. The effect is boiling point. named for the French physicist Pierre The composition and boiling points of Auger (1899–93). azeotropes vary with pressure, indicating that they are not chemical compounds. auric /ô-rik/ Designating a compound of Azeotropes may be broken by distillation gold(III). in the presence of a third liquid, by chemical reactions, adsorption, or fractional auric chloride /or-ik/ See gold(III) chlo- crystallization. See constant-boiling mix- ride. ture. aurous /ôr-ŭs/ Designating a compound azeotropic distillation A method used of gold(I). to separate mixtures of liquids that cannot be separated by simple distillation. Such a autocatalysis /aw-toh-kă-tal-ă-sis/ See mixture is called an azeotrope. A solvent is catalyst. added to form a new azeotrope with one of

26 azurite

N N OH

Azo compound

the components, and this is then removed mula RN:NR′, where R and R′ are aro- and subsequently separated in a second matic groups. Azo compounds can be column. An example of the use of formed by coupling a diazonium com- azeotropic distillation is the dehydration of pound with an aromatic phenol or amine. 96% ethanol to absolute ethanol. Most are colored because of the presence Azeotropic distillation is not widely used of the azo group –N:N–. because of the difficulty of finding inex- pensive non-toxic non-corrosive solvents azo dye An important type of dye used that can easily be removed from the new in acid dyes for wool and cotton. The dyes azeotrope. are azo compounds; usually sodium salts of sulfonic acids. azeotropic mixture See azeotrope. azo group See azo compound. azide /az-ÿd, -id, ay-zÿd/ 1. An inorganic – compound containing the ion N3 . 2. An organic compound of general for- azoimide /az-oh-im-ÿd, -id, ay-zoh-/ See hydrazoic acid. mula RN3. azine /az-een, -in/ An organic hetero- azulene /az-yŭ-leen/ (C10H8) A blue cyclic compound that has a hexagonal ring crystalline compound having a seven-mem- containing carbon and nitrogen atoms. bered ring fused to a five-membered ring. It Pyridine (C5H5N) is the simplest example. converts to naphthalene on heating. azo compound /az-oh, ay-zoh/ A type azurite /azh-ŭ-rÿt/ See copper(II) car- of organic compound of the general for- bonate.

27 B

Babo’s law /bah-bohz/ The principle lines in the spectrum of radiation emitted that if a substance is dissolved in a liquid by excited hydrogen atoms. The lines cor- (solvent) the vapor pressure of the liquid is respond to the atomic electrons falling into reduced; the amount of lowering is propor- the second lowest energy level, emitting en- tional to the amount of solute dissolved. ergy as radiation. The wavelengths (λ) of See also Raoult’s law. The law is named for the radiation in the Balmer series are given the German chemist Lambert Heinrich by: Clemens von Babo (1818–99). 1/λ = R(1/22 – 1/n2) where n is an integer and R is the Rydberg back e.m.f. An e.m.f. that opposes the constant. The series is named for the Swiss normal flow of electric charge in a circuit mathematician Johann Jakob Balmer or circuit element. In some electrolytic cells (1825–98). See Bohr theory. See also spec- a back e.m.f. is caused by the layer of hy- tral series. drogen bubbles that builds up on the cathode as hydrogen ions pick up electrons and banana bond (bent bond) 1. In form gas molecules (i.e. as a result of po- strained-ring compounds the angles as- larization of the electrode). sumed on the basis of hybridization are often not equal to the angles obtained by Bakelite /bay-kĕ-lÿt/ (Trademark)A joining the atomic centers. In these cases it common thermosetting synthetic polymer is sometimes assumed that the bonding or- formed by the condensation of phenol and bital is bent or banana-like in shape. Cy- methanal. clopropane is an example, in which geometric considerations imply a bond baking powder A mixture of sodium angle of 60° while sp3 hybridization im- hydrogencarbonate (sodium bicarbonate, plies an inter-orbital angle of around 100°, baking soda) and a weak acid such as tar- giving a banana bond. taric acid. The addition of moisture or 2. A multicentre bond of the type present in heating causes a reaction that produces such compounds as diborane (B2H6). bubbles of carbon dioxide gas, which make dough or cake mixture rise. H2 baking soda See sodium hydrogencar- C bonate. ball mill A device commonly used in the chemical industry for reducing the size of C solid material. Ball mills usually have H2C H2 slowly rotating steel-lined drums, which contain steel balls. The material is crushed by the tumbling action of the contents of Banana bond the drum. Compare hammer mill. band spectrum A spectrum that ap- Balmer series /bahl-mer/ A series of pears as a number of bands of emitted or

28 barium hydroxide absorbed radiation. Band spectra are char- This equilibrium was the basis of the to- acteristic of molecules. Often each band tally obsolete Brin process for the commer- can be resolved into a number of closely cial production of oxygen. spaced lines. The bands correspond to Barium is also notable for the very low changes of electron orbit in the molecules. solubility of the sulfate, which permits its The close lines seen under higher resolu- application to gravimetric analysis for ei- tion are the result of different vibrational ther barium or sulfate. Barium compounds states of the molecule. See also spectrum. give a characteristic green color to flames which is used in qualitative analysis. Bar- bar A unit of pressure defined as 105 ium salts are all highly toxic with the ex- pascals. The millibar (mb) is more com- ception of the most insoluble materials. mon; it is used for measuring atmospheric Metallic barium has the body-centered pressure in meteorology. cubic structure. Symbol: Ba; m.p. 729°C; b.p. 1640°C; Barft process A process formerly used r.d. 3.594 (20°C); p.n. 56; r.a.m. 137.327. for protecting iron from corrosion by heating it in steam, to form a layer of tri-iron barium bicarbonate See barium hydro- tetroxide (Fe3O4). gencarbonate. barites /bă-rÿ-teez/ See barium sulfate. barium carbonate (BaCO3) A white insoluble salt that occurs naturally as the bair-ee-ŭm barium / / A dense, low-melt- mineral witherite. Barium carbonate can ing reactive metal; the fifth member of be readily precipitated by adding an alkali group 2 (formerly IIA) of the periodic table carbonate to a barium salt solution. On and a typical alkaline-earth element. The heating it decomposes reversibly with the electronic configuration is that of xenon formation of the oxide and carbon dioxide: with two additional outer 6s electrons. BaCO ˆ BaO + CO Barium is of low abundance; it is found as 3 2 It is used as a rat poison. witherite (BaCO3) and barytes (BaSO4). The metal is obtained by the electrolysis of (BaCl ) A white solid the fused chloride using a cooled cathode barium chloride 2 which is slowly withdrawn from the melt. that can be prepared by dissolving barium Because of its low melting point barium is carbonate in hydrochloric acid and crystal- readily purified by vacuum distillation. lizing out the dihydrate (BaCl2.2H2O). Barium metal is used as a ‘getter’, i.e., a Barium chloride is used as the electrolyte in compound added to a system to seek out the extraction of barium, as a rat poison, the last traces of oxygen; and as an alloy and in the leather industry. constituent for certain bearing metals. Barium has a low ionization potential barium hydrogencarbonate (barium bi- and a large radius. It is therefore strongly carbonate; Ba(HCO3)2) A compound electropositive and its properties, and that occurs only in aqueous solution. It is those of its compounds, are very similar to formed by the action of cold water con- those of the other alkaline-earth elements taining carbon dioxide on barium carbon- calcium and strontium. Notable differ- ate, to which it reverts on heating: ences in the chemistry of barium from the BaCO3 + CO2 + H2O = Ba(HCO3)2 rest of the group are: 1. The much higher stability of the carbon- barium hydroxide (baryta; Ba(OH)2) ate. A white solid usually obtained as the oc- 2. The formation of the peroxide below tahydrate, Ba(OH)2.8H2O. Barium hy- 800°C. Barium peroxide decomposes on droxide is the most soluble of the group 2 strong heating to give oxygen and bar- hydroxides and can be used in volumetric ium oxide: analysis for the estimation of weak acids ˆ BaO2 BaO + O using phenolphthalein as an indicator. 29 barium oxide barium oxide (BaO) A white powder but H2O is also a base (although somewhat prepared by heating barium in oxygen or weaker) because it can accept a further + by thermal decomposition of barium car- proton to form H3O . In this treatment the bonate. It has been used in the manufacture ions of classical mineral acids such as 2– – of lubricating-oil additives. SO4 and NO3 are weak conjugate bases of their respective acids. Electron-pair barium peroxide (BaO2) A dense off- donors, such as trimethylamine and pyri- white powder that can be prepared by care- dine, are examples of organic bases. fully heating barium oxide in oxygen. Barium peroxide is used for bleaching base-catalyzed reaction A reaction straw and silk and in the laboratory prepa- catalyzed by bases. Typical base-catalyzed ration of hydrogen peroxide. reactions are the Claisen condensation and the aldol reaction, in which the first step is barium sulfate (BaSO4) A white solid abstraction of a proton to give a carbanion. that occurs naturally as the mineral barytes. Barium sulfate is very insoluble in base metal A metal such as iron, lead, water and can be prepared easily as a pre- or copper, distinguished from a noble cipitate by adding sulfuric acid to barium metal such as gold or silver. chloride. Barium sulfate is an important industrial chemical. Under the name of base unit A unit that is defined in terms ‘blanc fixe’ it is used as a pigment extender of reproducible physical quantities. See in surface coating compositions. It is also also SI units. used in the glass and rubber industries and medically (taken orally) to allow radi- basic Having a tendency to release OH– ographs to be taken of the digestive system. ions. Thus any solution in which the concentration of OH– ions is greater than that barn Symbol: b A unit of area defined as in pure water at the same temperature is 10–28 square meter. The barn is sometimes described as basic; i.e. the pH is greater used to express the effective cross-sections than 7. of atoms or nuclei in the scattering or absorption of particles. basic aluminum ethanoate See aluminum ethanoate. barrel A measurement of volume often used in the chemical industry. It is equal to basic oxide An oxide of a metal that re- 159 liters (about 29 US gallons). acts with water to form a base, or with an acid to form a salt and water. For example, baryta /bă-rÿ-tă/ See barium hydroxide. calcium oxide reacts with water to form calcium hydroxide: → barytes /bă-rÿ-teez/ (heavy spar) A min- CaO + H2O Ca(OH)2 eral form of barium sulfate (BaSO4). and with hydrochloric acid to produce calcium chloride and water: → basalt /bă-sawlt, bass-awlt/ A dark-col- CaO + 2HCl CaCl2 + H2O ored basic igneous rock derived from solid- See also acidic oxide. ified volcanic lava. It consists mainly of fine crystals of pyroxine and plagioclase basic oxygen process See Bessemer feldspar. process. base A compound that releases hydroxyl basic salt A compound intermediate be- ions, OH–, in aqueous solution. Basic solu- tween a normal salt and a hydroxide or tions have a pH greater than 7. In the oxide. The term is often restricted to Lowry-Brønsted treatment a base is a sub- hydroxyhalides (such as Pb(OH)Cl, stance that tends to accept a proton. Thus Mg2(OH)3Cl2.4H2O, and Zn(OH)F) and – + OH is basic as it accepts H to form water, hydroxy-oxy salts (for example, 2PbCO3. 30 benzene

Pb(OH)2, Cu(OH)2.CuCl2, Cu(OH)2. Beckmann thermometer /bek-măn/A CuCo3). The hydroxyhalides are essen- type of thermometer designed to measure tially closely packed assemblies of OH– differences in temperature rather than scale with metal or halide ions in the octahedral degrees. Beckmann thermometers have a holes. The hydroxy-oxy salts have more larger bulb than common thermometers complex structures than those implied by and a stem with a small internal diameter, the formulae. so that a range of 5°C covers about 30 centimeters in the stem. The mercury bulb is basic slag See slag. connected to the stem in such a way that the bulk of the mercury can be separated batch process A manufacturing process from the stem once a particular 5° range in which the reactants are fed into the has been attained. The thermometer can process in fixed quantities (batches), rather thus be set for any particular range of than in a continuous flow. At any particu- working temperature. It is named for the lar instant all the material, from its prepa- German chemist Ernst Otto Beckmann ration to the final product, has reached a (1853–1923). definite stage in the process. Baking a cake is an example of a batch process. Such becquerel /bek-ĕ-rel/ Symbol: Bq The SI processes present problems of automation unit of activity equal to the activity of a ra- and instrumentation and tend to be waste- dioactive substance that has one spontaneous nuclear change per second; 1 Bq = 1 ful of energy. For this reason, batch pro- –1 cessing is only economically operated on s . The unit is named for the French physicist Antoine Henri Becquerel (1852–1908). an industrial scale when small quantities of valuable or strategic materials are re- beneficiation /ben-ĕ-fish-ee-ay-shŏn/ The quired, e.g. drugs, titanium metal. Com- process of separating an ore into a useful pare continuous process. component and waste material (known as gangue). The process is sometimes de- battery A number of similar units, such scribed as ore dressing. as electric cells, working together. Many dry ‘batteries’ used in radios, flashlights, bent bond See banana bond. etc., are in fact single cells. If a number of identical cells are connected in series, the bentonite /ben-tŏ-nÿt/ A type of clay total e.m.f. of the battery is the sum of the that is used as an adsorbent in making e.m.f.s of the individual cells. If the cells are paper. The gelatinous suspension it forms in parallel, the e.m.f. of the battery is the with water is used to bind together the same as that of one cell, but the current sand for making iron castings. Chemically drawn from each is less (the total current is bentonite is an aluminosilicate of variable split among the cells). composition. bauxite // A mineral hydrated form of bent sandwich compound See sand- aluminum hydroxide; the principal ore of wich compound. aluminum. benzaldehyde /ben-zal-dĕ-hÿd/ See ben- b.c.c. See body-centered cubic crystal. zenecarbaldehyde.

Beckmann rearrangement /bek- benzene /ben-zeen, ben-zeen/ (C6H6)A măn/ A type of reaction in which the colorless liquid hydrocarbon with a char- OXIME of a ketone is converted into an acteristic odor. Benzene is a highly toxic amide using a sulfuric acid catalyst. First compound and continued inhalation of the discovered by the German chemist Ernst vapor is harmful. It was originally isolated Otto Beckmann (1853–1923), it is used in from coal tar and for many years this was the manufacture of polyamides. the principal source of the compound.

31 benzenecarbaldehyde

Kekulé structures

Dewar structures

Benzene structures

Contemporary manufacture is from by the usual methods of aldehyde synthe- hexane; petroleum vapor is passed over sis. It is used as a food flavoring and in the platinum at 500°C and at 10 atmospheres manufacture of dyes and antibiotics, and pressure: can be readily manufactured by the chlori- → C6H14 C6H6 + 4H2 nation of methylbenzene and the subse- Benzene is the simplest aromatic hydro- quent hydrolysis of (dichloromethyl) carbon. It shows characteristic elec- benzene: trophilic substitution reactions, which are → C6H5CH3 + Cl2 C6H5CHCl2 difficult to explain assuming a simple un- → C6H5CHCl2 + 2H2O C6H5CH(OH)2 saturated structure (such as Kekulé’s + 2HCl (1865) or Dewar’s (1867) formulae). This C H CH(OH) → C H CHO + H O anomolous behavior can now be explained 6 5 2 6 5 2 by assuming that the six pi electrons are de- benzenecarbonyl chloride /ben-zeen- localized and that benzene is, therefore, a kar-bŏ-nil/ (benzoyl chloride; C H COCl) resonance hybrid. It consists of two Kekulé 6 5 A liquid acyl chloride used as a benzoylat- structures and three Dewar structures, the former contributing 80% and the latter ing agent. 20% to the hybrid. Benzene is usually represented by either a Kekulé structure or a benzenecarbonyl group (benzoyl hexagon containing a circle (which denotes group) The group C6H5.CO–. the delocalized electrons). benzenecarboxylic acid /ben-zeen-kar- benzenecarbaldehyde /ben-zeen-kar-bal- boks-il-ik/ (benzoic acid; C6H5COOH) dĕ-hÿd/ (benzaldehyde; C6H5CHO) A A white crystalline carboxylic acid. It is yellow organic oil with a distinct almond- used as a food preservative. The carboxyl like odor. Benzenecarbaldehyde undergoes group (–COOH) directs further substitu- the reactions characteristic of aldehydes tion onto the benzene ring in the 3 posi- and may be synthesized in the laboratory tion.

32 benzoyl group benzene-1,2-dicarboxylic acid (ph- OH H thalic acid; C6H4(COOH)2) A white C CH2 crystalline aromatic acid. On heating it CH loses water to form phthalic anhydride, which is used to make dyestuffs and poly- CH CH mers for plasticizers and plastics. C H benzyl alcohol benzene-1,4-dicarboxylic acid (tereph- benzyl alcohol thalic acid; C6H4(COOH)2) A colorless crystalline organic acid used to produce O Dacron and other polyesters. H C CH CH benzene-1,3-diol (resorcinol; C6H4(OH)2) A white crystalline phenol used in the manufacture of dyestuffs and celluloid. CH CH C benzaldehyde H benzaldehyde benzene-1,4-diol (hydroquinone, quinol; C6H4(OH)2) A white crystalline phenol used in making dyestuffs. See also quinone. O H benzene ring The cyclic hexagonal C C arrangement of six carbon atoms that are CH OH characteristic of AROMATIC COMPOUNDS, i.e. of BENZENE and its derivatives. CH CH C benzoic acid benzenesulfonic acid /ben-zeen-sul-fon- H benzoic acid ik/ (C6H5SO2OH) A white crystalline Benzene compounds acid made by sulfonation of benzene. Any further substitution onto the benzene ring is directed into the 3 position. benzfuran /benz-fyoo-ran, -fyoo-ran/ benzoic acid /ben-zoh-ik/ See benzenecarboxylic acid. (coumarone; C8H6O) A crystalline compound having a benzene ring fused to a furan ring. benzole /ben-zohl/ A mixture of mainly aromatic hydrocarbons obtained from benzil See Benzilic acid rearrangement. coal. See also benzene. /ben-zoh-pÿ-reen/ See benzilic acid rearrangement /ben-zil- benzopyrene benzpyrene. ik/ A reaction in which benzil (1,2- diphenylethan-1,2-dione) is treated with benzoquinone /ben-zoh-kwi-nohn/ See hydroxide and then with acid to give ben- quinone. zilic acid (2-hydroxy-2,2-diphenylethanoic acid): benzoylation /ben-zoh-ă-lay-shŏn/ See → C6H5.CO.CO.C6H5 acylation. (C6H5)2C(OH).COOH The reaction, which involves migration of benzoyl chloride /ben-zoh-ăl/ See ben- a phenyl group (C6H5–) from one carbon zenecarbonyl chloride. atom to another, was the first rearrangement reaction to be described (by Justus benzoyl group See benzenecarbonyl von Liebig in 1828). group.

33 benzpyrene benzpyrene /benz-pÿ-reen/ (benzopyrene; the electronic configuration of helium with C20H12) A cyclic aromatic hydrocarbon two additional outer 2s electrons. with a structure consisting of five fused Beryllium occurs in a number of miner- benzene rings. It occurs in coal tar and to- als such as beryllonite (NaBePO4), bacco smoke and has strong carcinogenic chrysoberyl (Be(AlO2)2), bertrandite properties. (4BeO.2SiO2), and beryl (3BeO.Al2O3. 6SiO2). The element accounts for only benzpyrrole /benz-pi-rohl/ See indole. 0.0006% by mass of the Earth’s crust. The metal is obtained by conversion of the ore benzyl alcohol /ben-zăl/ See phenyl- to the sulfate at high temperature and pres- methanol. sure with concentrated sulfuric acid, then to the chloride, followed by electrolysis of benzyl group The group C6H5CH2–. the fused chloride. Alternatively, extraction by hydrogen fluoride followed by elec- benzyne /ben-zÿn/(C6H4) A short-lived trolysis of the fused fluoride may be intermediate present in some reactions. employed. The metal has a much lower The ring of six carbon atoms contains two general reactivity than lithium or other ele- double bonds and one triple bond (the sys- ments in group 2. It is used as an antioxi- tematic name is 1,2-didehydrobenzene). dant and hardener in some alloys, such as copper and phosphor bronzes. Bergius process /ber-gee-ŭs/ A process Beryllium has the highest ionization po- formerly used for making hydrocarbon tential of group 2 and the smallest size. fuels from coal. A powdered mixture of Consequently it is less electropositive and coal, heavy oil, and a catalyst was heated more polarizing than other members of the with hydrogen at high pressure. The group. Thus, Be2+ ions do not exist as such process is named for the German industrial in either solids or solutions, and even with chemist Friedrich Karl Rudolph Bergius the most electronegative elements there is (1884–1949). partial covalent character in the bonds. The metal reacts directly with oxygen, ni- berkelium /ber-klee-ŭm, ber-kee-lee- trogen, sulfur, and the halogens at various ŭm/ A silvery radioactive transuranic ele- elevated temperatures, to form the oxide ment of the actinoid series of metals, not BeO, nitride Be3N2, sulfide BeS, and found naturally on Earth. Several radioiso- halides BeX2, all of which are covalent. topes have been synthesized. The metal re- Beryllium does not react directly with hy- acts with oxygen, steam, and acids. drogen but a polymeric hydride (BeH2)n ° Symbol: Bk; m.p. 1050 C; p.n. 97; r.d. can be prepared by reduction of (CH3)2Be 14.79 (20°C); most stable isotope 247Bk using lithium tetrahydridoaluminate. (half-life 1400 years). Beryllium is amphoteric forming beryl- 2– late species, such as [Be(OH)4] and 3+ beryl A mineral, 3BeO.Al2O3.6SiO2, [Be(OH)]3 . The hydroxide is only weakly used as a source of beryllium. There are basic. The element does not form a true several varieties including the gemstones carbonate; the basic beryllium carbonate, emerald (colored green by traces of BeCO3.Be(OH)2 is formed when sodium chromium oxide) and aquamarine (a blue- carbonate is added to solutions of beryl- green color). lium compounds. Beryllium hydride, chloride, and di- beryllate /bĕ-ril-ayt/ See beryllium; methylberyllium form polymeric bridged beryllium hydroxide. species but, whereas the bridging in the chloride is via an electron pair on chlorine beryllium /bĕ-ril-ee-ŭm/ A light metallic atoms and can be regarded as an electron- element, similar to aluminum but some- pair donor bond, the bonding in the hy- what harder; the first element in group 2 dride and in the methyl compound involves (formerly IIA) of the periodic table. It has two-electron three-centre bonds. Coordi-

34 bicarbonate nation compounds are quite common with by the decomposition of beryllium hydrox- beryllium; some examples include ide or carbonate. Beryllium oxide is insolu- 2– [BeCl4] , (R2O)2BeCl2, and ble in water but it shows basic properties [Be(NH3)4]Cl2. Beryllium also forms a by dissolving in acids to form beryllium number of alkyl compounds, some of salts: + → 2+ which can be stabilized by coordination. BeO + 2H Be + H2O Beryllium is extremely toxic. However, beryllium oxide also resem- Symbol: Be; m.p. 1278±5°C; b.p. bles acidic oxides by reacting with alkalis 2970°C (under pressure); r.d. 1.85 (20°C); to form beryllates: p.n. 4; r.a.m. 9.012182. – → 2– BeO + 2OH + H2O Be(OH)4 It is thus an amphoteric oxide. Beryl- beryllium bicarbonate See beryllium lium oxide is used for the production of hydrogencarbonate. beryllium and beryllium-copper refractories, for high-output transistors, and for beryllium bronze See bronze. printed circuits. The chemical properties of beryllium oxide are similar to those of alu- beryllium carbonate (BeCO3) An un- minum oxide. stable solid prepared by prolonged treatment of a suspension of beryllium beryllium sulfate (BeSO4) An insoluble hydroxide with carbon dioxide. The result- salt prepared by the reaction of beryllium ing solution is evaporated and filtered in an oxide with concentrated sulfuric acid. On atmosphere of carbon dioxide. heating, it breaks down to give the oxide. When heated in the presence of water, it beryllium chloride (BeCl ) A white 2 readily dissolves to give an acidic solution. solid obtained by passing chlorine over a heated mixture of beryllium oxide and car- Bessemer process /bess-ĕ-mer/A bon. It is a poor conductor in the fused process for making steel from pig iron. A state and in the solid form consists of a co- vertical cylindrical steel vessel (converter) valent polymeric structure. It is readily sol- is used, lined with a refractory material. uble in organic solvents but is hydrolyzed in the presence of water to give the hy- Air is blown through the molten iron and droxide. The anhydrous salt is used as a carbon is oxidized and thus removed from catalyst. the iron. Other impurities – silicon, sulfur, and phosphorus – are also oxidized. Irons beryllium hydrogencarbonate (beryl- containing large amounts of phosphorus are treated in a converter lined with a basic lium bicarbonate; Be(HCO3)2) A compound formed in solution by the action of material, so that a phosphate slag is carbon dioxide on a suspension of the car- formed. The required amount of carbon is bonate, to which it reverts on heating: then added to the iron to produce the desired type of steel. The process is named for BeCO3 + CO2 + H2O = Be(HCO3)2 the British inventor and engineer Sir Henry beryllium hydroxide (Be(OH)2)A Bessemer (1813–98). solid that can be precipitated from beryllium-containing solutions by an alkali. In beta particle An electron emitted by a an excess of alkali, beryllium hydroxide radioactive substance as it decays. 2– dissolves to give a beryllate, Be(OH)4 . In this way, beryllium and aluminum hydrox- bi- Prefix used formerly in naming acid ides are similar and the reaction is an indi- salts. The prefix indicates the presence of cation that beryllium hydroxide is hydrogen; for instance, sodium bisulfate amphoteric. (NaHSO4) is sodium hydrogensulfate, etc. beryllium oxide (BeO) A white solid bicarbonate /bÿ-kar-bŏ-nayt,-nit/ See formed by heating beryllium in oxygen or hydrogencarbonate.

35 bimolecular bimolecular /bÿ-mŏ-lek-yŭ-ler/De- biphenyl /bÿ-fen-ăl, -fee-năl/ (C6H5C6H5) scribing a reaction or step that involves An organic compound having a structure two molecules, ions, etc. A common exam- in which two phenyl groups are joined by a ple of this type of reaction is the decompo- C–C bond. See also polychlorinated sition of hydrogen iodide, biphenyl. → 2HI H2 + I2 takes place between two molecules and is bipyridyl /bÿ-pÿ-ră-dăl/ See dipyridyl. therefore a bimolecular reaction. Other common examples are: Birkeland–Eyde process /berk-lănd ÿ-dĕ/ H O + I → OH– + HIO An industrial process for fixing nitrogen 2 2 2 (as nitrogen monoxide) by passing air OH– + H+ → H O 2 through an electric arc: All bimolecular reactions are second N + O → 2NO order, but some second-order reactions are 2 2 The process is named for the Norwe- not bimolecular. gian physicist and chemist Kristian Olaf Bernhard Birkeland (1867–1917) and the binary compound A chemical com- Norwegian engineer and industrialist pound formed from two elements; e.g. Samuel Eyde (1866–1940). See also nitro- Fe2O3 or NaCl. gen fixation. biochemical oxygen demand (BOD) bismuth /biz-mŭth/ A brittle pinkish The amount of oxygen taken from natural metallic element belonging to group 15 water by microorganisms that decompose (formerly VA) of the periodic table. It oc- organic waste matter in the water. It is curs native and in the ores Bi2S3 and Bi2O3. therefore a measure of the quantity of or- The element does not react with oxygen or ganic pollutants present. It is found by water under normal temperatures. It can measuring the amount of oxygen in a sam- be dissolved by concentrated nitric acid. ple of water, keeping the sample and then Bismuth is widely used in alloys, especially making the measurement again five days low-melting alloys. The element has the later. property of expanding when it solidifies. Compounds of bismuth are used in cos- biochemistry The study of chemical metics and medicines. ° compounds and reactions occurring in liv- Symbol: Bi; m.p. 271.35 C; b.p. ± ° ° ing organisms. 1560 5 C; r.d. 9.747 (20 C); p.n. 83; r.a.m. 208.98037. biodegradable /bÿ-oh-di-gray-dă-băl/ See dÿ-oks- pollution. bismuth(III) carbonate dioxide / ÿd, -id/ (bismuthyl carbonate; Bi2O2CO3) A white solid prepared by mixing solutions bioinorganic chemistry /bÿ-oh-in-or- of bismuth nitrate and ammonium carbon- gan-ik/ The study of biological molecules ate. It contains the (BiO)+ ion. that contain metal atoms or ions. Many enzymes have active metal atoms and bismuth(III) chloride (bismuth trichlo- bioinorganic compounds are important in ride; BiCl3) A white deliquescent solid. It other roles such as protein folding, oxygen can be prepared by direct combination of transport, and electron transfer. Two im- bismuth and chlorine. Bismuth(III) chlo- portant examples of bioinorganic com- ride dissolves in excess dilute hydrochloric pounds are hemoglobin (containing iron) acid to form a clear liquid, but if diluted it and chlorophyll (containing magnesium). produces a white precipitate of bismuth(III) chloride oxide (bismuthyl biosynthesis /bÿ-oh-sin-th’ĕ-sis/ The re- chloride, BiOCl): actions by which organisms obtain the var- BiCl3 + H2O = BiOCl + 2HCl ious compounds needed for life. This reaction is often used as an exam-

36 blende ple of a reversible reaction and as a confir- gas, coal tar, and water. It is the common matory test for bismuth during quantita- type of coal used for domestic and indus- tive analysis. Bismuth(V) chloride does not trial purposes. See also anthracite. form. biuret /bÿ-yû-ret, bÿ-yoo-ret/ (H2NCON- bismuth(III) chloride oxide See bis- HCONH2) A colorless crystalline or- muth(III) chloride. ganic compound made by heating UREA (carbamide). It is used in a chemical test for bismuth(III) nitrate oxide (bismuthyl ni- PROTEINS. trate; BiONO3) A white insoluble solid, often referred to as bismuth subnitrate. It is bivalent /bÿ-vay-lĕnt, biv-ă-/ (divalent) precipitated when bismuth(III) nitrate is di- Having a valence of two. luted and contains the (BiO)+ ion. Bis- muth(III) nitrate oxide is used in blackdamp See firedamp. pharmaceutical preparations. blanc fixe /blahng-feeks/ See barium bismuth trichloride /trÿ-klor-ÿd, -kloh- sulfate. rÿd/ See bismuth(III) chloride. blast furnace A furnace for producing bismuthyl carbonate /biz-mŭ-thăl/ See iron from iron(III) oxide. A mixture of the bismuth(III) carbonate dioxide. ore with coke and a flux is heated by pre- heated air blown into the bottom of the bismuthyl chloride See bismuth(III) furnace. The flux is often calcium oxide chloride. (from limestone). Molten pig iron is run off from the bottom of the furnace. bismuthyl compound A compound containing the (BiO)+ ion or BiO grouping. bleach Any substance used to remove color from materials such as cloth and bismuthyl ion See bismuth(III) carbon- paper. All bleaches are oxidizing agents, ate dioxide. and include chlorine, sodium chlorate(I) solution (NaClO, sodium hypochlorite), bismuthyl nitrate See bismuth(III) nitrate oxide. hydrogen peroxide, and sulfur(IV) oxide. Sunlight also has a bleaching effect. bisulfate /bÿ-sul-fayt/ See hydrogensulfate. bleaching powder A white solid that can be regarded as a mixture of calcium bisulfite /bÿ-sul-fÿt/ See hydrogensulfite. chlorate(I) (calcium hypochlorite), calcium chloride, and calcium hydroxide. It is pre- bisulfite addition compound See alde- pared on a large scale by passing a current hyde. of chlorine through a tilted cylinder down which is passed calcium hydroxide. Bleach- bittern /bit-ern/ The liquid that is left ing powder has been used for bleaching after sodium chloride has been crystallized paper pulps and fabrics and for sterilizing from sea water. water. Its bleaching power arises from the formation, in the presence of air containing bitumen /bă-tew-mĕn, bich-û-mĕn/A carbon dioxide, of the oxidizing agent mixture of solid or semisolid hydrocarbons chloric(I) acid (hypochlorous acid, HClO): → obtained from coal, oil, etc. See tar. Ca(ClO)2.Ca(OH)2.CaCl2 + 2CO2 2CaCO3 + CaCl2 + 2HClO bituminous coal /bă-tew-mĕ-nŭs/A type of second-grade coal, containing more blende /blend/ A naturally occurring sul- than 65% carbon but also quantities of fide ore.

37 block copolymer block copolymer See polymerization. This means that orbits are possible only when the angular momentum (mvr) is an blue vitriol /vit-ree-ŏl/ Copper(II) sul- integral number of units of h/2π. Angular fate pentahydrate (CuSO4.5H2O). momentum is thus quantized. In fact, Bohr in his theory did not use the wave behavior boat conformation See conformation. of the electron to derive this relationship. He assumed from the beginning that angu- BOD See biochemical oxygen demand. lar momentum was quantized in this way. Using the above expressions it can be body-centered cubic crystal (b.c.c.)A shown that the electron energy is given by 4 ε 2 2 2 crystal structure in which the unit cell has E = –me /8 0 n h an atom, ion, or molecule at each corner of Different values of n (1, 2, 3, etc.) cor- a cube and at the center of the cube. In this respond to different orbits with different type of structure the coordination number energies; n is the principal quantum num- is 8. It is less close-packed than the face- ber. In making a transition from an orbit n1 centered cubic structure. The alkali metals to another orbit n2 the energy difference form crystals with body-centered cubic ∆W is given by: ∆ 4 2 structures. W = W1 – W2 = me (1/n2 – 2 ε 2 2 1/n1 )/8 0 h bohrium /bor-ee-ŭm, boh-ree-/ A syn- This is equal to hv where v is the fre- thetic radioactive element first detected by quency of radiation emitted or absorbed. bombarding a bismuth target with Since vλ = c, then λ 4 2 2 ε 2 3 chromium nuclei. Only a small number of 1/ = me (1/n1 – 1/n2 )/8 0 ch atoms have ever been produced. The theory is in good agreement with Symbol: Bh; p.n. 107; most stable iso- experiment in predicting the wavelengths tope 262Bh (half life 0.1s). of lines in the hydrogen spectrum, although it is less successful for larger Bohr magneton /bor, bohr/ See magne- ATOMS. Different values of n1 and n2 corre- ton. spond to different spectral series, with lines given by the expression: λ 2 2 Bohr theory A theory introduced in 1/ = R(1/n1 – 1/n2 ) 1911 to explain the spectrum of atomic hy- R is the Rydberg constant. Its experi- drogen. The model he used was that of a mental value is 1.096 78 × 107 m–1. The 4 πε 2 2 nucleus with charge +e, orbited by an elec- value from Bohr theory (me /8 1 ch ) is tron with charge –e, moving in a circle of 1.097 00 × 107 m–1. radius r. If v is the velocity of the electron, The theory is named for the Danish the centripetal force, mv2/r is equal to the physicist Niels Bohr (1885–1962). 2 πε 2 force of electrostatic attraction, e /4 0r . Using this, it can be shown that the total boiling The process by which a liquid is energy of the electron (kinetic and poten- converted into a gas or vapor by heating at 2 πε tial) is –e /8 0r. its boiling point. At this temperature the If the electron is considered to have vapor pressure of the liquid is equal to the wave properties, then there must be a external pressure, and bubbles of vapor whole number of wavelengths around the can form within the liquid. orbit, otherwise the wave would be a progressive wave. For this to occur boiling point The temperature at which nλ = 2πr the vapor pressure of a liquid is equal to at- where n is an integer, 1, 2, 3, 4, …. The mospheric pressure. This temperature is al- wavelength, λ, is h/mv, where h is the ways the same for a particular liquid at a Planck constant and mv the momentum. given pressure (for reference purposes usu- Thus for a given orbit: ally taken as standard pressure). See also nh/2π = mvr elevation of boiling point.

38 bond enthalpy boiling-point-composition diagram A entropy S of a system is related to the num- diagram for a two-component liquid sys- ber W of distinguishable ways in which the tem representing both the variation of the system can exist by the equation: S = k boiling point and the composition of the lnW, where k is the Boltzmann constant. vapor phase as the liquid-phase composi- This formula is a quantitative expression tion is varied. A mixture of A and B at of the idea that the entropy of a system is a composition L1 would have a boiling point measure of its disorder. It was discovered T1 and a vapor composition V1, which by Ludwig Boltzmann in the late 19th cen- when condensed would give a liquid at L2. tury in the course of his investigations into L2 would boil at T2 to give vapor V2 equiv- the foundations of statistical mechanics. alent to liquid of composition L3, and so on. Thus the whole process of either distil- bomb calorimeter A sealed insulated lation or fractionation of this system will container, used for measuring energy re- lead to progressive enrichment in compo- leased during combustion of substances nent A. (e.g. foods and fuels). A known amount of For perfect solutions obeying Raoult’s the substance is ignited inside the calorime- law the curves would coincide but in real ter in an atmosphere of pure oxygen, and cases there will be sufficient intermolecular undergoes complete combustion at con- attraction to cause deviation from this. The stant volume. The resultant rise in temper- separation of the curves as well as the dif- ature is related to the energy released by ference in boiling points determines the the reaction. Such energy values (calorific performance of fractionation columns. See values) are often quoted in joules per kilo- also constant-boiling mixture. gram (J kg–1).

Temperature bond The interaction between atoms, molecules, or ions holding these entities together. The forces giving rise to bonding may vary from extremely weak intermolecular forces, about 0.1 kJ mol–1, to very V1 T1 strong chemical bonding, about 103 kJ V2 T2 mol–1. See bond energy; bond length; coor- T3 V3 dinate bond; covalent bond; electrovalent bond; hydrogen bond; metallic bond.

bond dissociation energy See bond energy. L4 L3 L2 L1 Temperature 100%A Composition 100%B bond energy The energy involved in Boiling point–composition diagram forming a bond. For ammonia, for instance, the energy of the N–H bond is one third of the energy involved for the process → NH3 N + 3H Boltzmann constant /bohlts-măn, -mahn/ It is thus one third of the heat of atomiza- Symbol: k The constant 1.380 54 J K–1, tion. Strictly speaking bond enthalpy equal to the gas constant (R) divided by the should be used. Avogadro constant (NA). The constant is The bond dissociation energy is a dif- named for the Austrian theoretical physi- ferent quantity to the bond energy. It is the cist Ludwig Edward Boltzmann (1844– energy required to break a particular bond 1906). See also degrees of freedom. in a compound, e.g.: → NH3 NH2 + H Boltzmann formula A fundamental result in statistical mechanics stating that the bond enthalpy See bond energy.

39 bonding orbital bonding orbital See orbital. ization occurs to give polydioxoboric(III) acid. bond length The length of a chemical BOND, the distance between the centers of boride /bor-ÿd, boh-rÿd/ A compound of the nuclei of two atoms joined by a chemi- boron, especially one with a more elec- cal bond. Bond lengths may be measured tropositive element. by electron or x-ray diffraction. Born–Haber cycle /born hay-ber/A boracic acid /bŏ-rass-ik/ See boric acid. cycle used in calculating the lattice energies of solids. The steps involved are: boranes /bor-aynz, boh-raynz/ See boron Atomization of sodium: → ∆ hydrides. Na(s) Na(g) H1 Ionization of sodium: → + ∆ borate /bor-ayt, boh-rayt/ See boron. Na(g) Na (g) H2 Atomization of chlorine: → ∆ borax /bor-aks, boh-raks/ See disodium Cl2(g) 2Cl(g) H3 tetraborate decahydrate. Ionization of chlorine: – → – ∆ Cl(g) + e Cl (g) H4 borax-bead test A preliminary test in Formation of solid: + – → ∆ qualitative inorganic analysis that can be a Na (g) + Cl (g) NaCl(s) H5 guide to the presence of certain metals. A This last step involves the lattice energy ∆ borax bead is formed by heating a little H5. The sum of all these enthalpies is borax on a loop in a platinum wire. A equal to the heat of the reaction: ½ → minute sample is introduced into the bead Na(s) + Cl2(g) NaCl(s) and the color observed in both the oxidiz- The cycle is named for the German ing and reducing areas of a Bunsen-burner physicist Max Born (1882–1970) and the flame. The color is also noted when the German physical chemist Fritz Haber bead is cold. (1868–1934). See also Hess’s law. boric acid /bor-ik, boh-rik/ (boracic acid; borohydride ions /bor-oh-hÿ-drÿd, boh- H3BO3) A white crystalline solid soluble roh-/ See boron hydride. in water; in solution it is a very weak acid. Boric acid is used as a mild antiseptic eye boron /bor-on, boh-ron/ A hard rather lotion and was formerly used as a food brittle metalloid element of group 3 (for- preservative. It is used in glazes for enam- merly IIIA) of the periodic table. It has the eled objects and is a constituent of Pyrex electronic structure 1s22s22p1. Boron is of glass. low abundance (0.0003%) but the natural Trioxoboric(III) acid is the full system- minerals occur in very concentrated forms atic name for the solid acid and it exists in as either borax (Na2B4O7.10H2O) or cole- this form in its dilute solutions. However, manite (Ca2B6O11). The element is ob- in more concentrated solutions polymer- tained by conversion to boric acid followed

BORAX-BEAD COLORS (H = hot; C = cold) Metal Oxidizing flame Reducing flame chromium green H+C green H+C cobalt blue H+C blue H+C copper green H, blue C often opaque iron brown-red H, yellow C green H+C manganese violet H+C colourless H+C nickel red–brown C gray–black C

40 boron hydrides by dehydration to B2O3 then reduction ammonia. There is also a ‘diamond-like’ with magnesium. High-purity boron for form of B–N which is claimed to be even semiconductor applications is obtained by harder than diamond. conversion to boron trichloride, which can Elemental boron reacts directly with be purified by distillation, then reduction fluorine and chlorine but for practical pur- using hydrogen. Only small quantities of poses the halides are obtained via the BF3 elemental boron are needed commercially; route from boric acid: → the vast majority of boron supplied by the B2O3 + 3CaF2 + 3H2SO4 3CaSO4 + industry is in the form of borax or boric 3H2O + 2BF3 → acid. BF3 + AlCl3 AlF3 + BCl3 As boron has a small atom and has a These halides are all covalent mol- relatively high ionization potential its com- ecules, which are all planar and trigonal in pounds are predominantly covalent; the shape. Boron halides are industrially im- ion B3+ does not exist. Boron does not react portant as catalysts or promoters in a vari- directly with hydrogen to form boron hy- ety of organic reactions including drides (boranes) but the hydrolysis of mag- polymerization and Friedel–Crafts type nesium boride does produce a range of alkylations. The decomposition of boron boranes such as B4H10, B5H9, and B6H10. halides in atmospheres of hydrogen at ele- Thermal decomposition of these higher bo- vated temperatures is also used to deposit ranes produces, among other things, the traces of pure boron in semiconductor de- simplest borane, B2H6 (diborane). The vices. species BH3 is only a short-lived reaction Boron forms a range of compounds intermediate. with elements that are less electronegative Finely divided boron burns in oxygen than itself, called borides. Borides such as ° above 600 C to give the oxide, B2O3, an ZrB2 and TiB2 are hard refractory sub- acidic oxide which will dissolve slowly in stances, which are chemically inert and water to give boric acid (B(OH)3) and have remarkably high electrical conductiv- rapidly in alkalis to give borates such as ities. Borides have a wide range of stoi- Na2B4O7. A number of polymeric species chiometries, from M4B through to MB6, with B–B and B–O links are known, e.g. a and can exist in close-packed arrays, lower oxide (BO)x, and a polymeric acid chains, and two-dimensional nets. Natural 10 (HBO2)n. Although the parent acid is boron consists of two isotopes, B weak, many salts containing borate anions (18.83%) and 11B (81.17%). These per- are known but their stoichiometry gives lit- centages are sufficiently high for their de- tle indication of their structure, many of tection by splitting of infrared absorption which are cyclic or linear polymers. These or by n.m.r. spectroscopy. contain both BO3 planar groups and BO4 Both borax and boric acid are used as tetrahedra. Boric acid and the borates give mild antiseptics and are not regarded as a range of glassy substances on heating; toxic; boron hydrides are however highly these contain cross-linked B–O–B chains toxic. and nets. In the molten state these materi- Symbol: B; m.p. 2300°C; b.p. 2658°C; als react with metal ions to form borates, r.d. 2.34 (20°C); p.n. 5; r.a.m. 10.811. which on cooling give characteristic colors to the glass. See borax-bead test. boron hydrides (boranes) Hydrides of Boron reacts with nitrogen on strong boron ranging from B2H6 to B20H16, which heating (1000°C) to give boron nitride, a have complex molecular structures. These slippery white solid with a layer structure compounds are notable for containing similar to that of graphite, i.e., hexagonal B–H–B bonds. Investigations have shown rings of alternating B and N atoms. The that the boron hydrides are electron defi- material has an extremely high melting cient and thus the bonding can only be ra- point and is thermally very stable but there tionalized in terms of MULTICENTER BONDS. is sufficient bond polarity in the B–N links The compound B2H6 can be prepared by to permit slow hydrolysis by water to give reacting boron trichloride with hydrogen.

41 boron nitride

A complex ion, tetrahydridoborate(III) bowl classifier A device that separates – (borohydride, BH4 ), can be formed; it has solid particles in a mixture of solids and very strong reducing properties. Other, liquid into fractions according to particle more complex, borohydride ions exist. size. Feed enters the center of a shallow bowl, which contains revolving blades. boron nitride (BN) A compound The coarse solids collect on the bottom, formed by heating BORON in nitrogen fine solids at the periphery. (1000°C). It has two crystalline forms. Boyle’s law At a constant temperature, boron oxide (B2O3) A glassy hygro- the pressure of a fixed mass of a gas is in- scopic solid that eventually forms boric versely proportional to its volume: i.e. acid. It forms various salts but also exhibits pV = K some amphoteric properties. where K is a constant. The value of K depends on the temperature and on the na- boron tribromide (BBr3) A colorless ture of the gas. The law holds strictly only liquid. See boron trichloride. for ideal gases. Real gases follow Boyle’s law at low pressures and high tempera- boron trichloride /trÿ-klor-ÿd, -kloh-rÿd/ tures. The law is named for the British (BCl3) A fuming liquid made by passing chemist and physicist Robert Boyle dry chlorine over heated boron. It is (1627–91). See gas laws. rapidly hydrolysed by water: → BCl3 + 3H2O 3HCl + H3BO3 Brackett series /brak-it/ See hydrogen As there are only three pairs of shared atom spectrum. electrons in the outer shell of the boron atom, boron halides form very stable addi- Brady’s reagent /bray-dee/ See 2,4-dini- tion compounds with ammonia by the ac- trophenylhydrazine. ceptance of a lone electron pair in a coordinate bond to complete a shared Bragg equation /brag/ An equation octet. used to deduce the crystal structure of a material using data obtained from x-rays boron trifluoride (BF3) A colorless directed at its surface. The conditions fuming gas made by heating a mixture of under which a crystal will reflect a beam of boron oxide, calcium fluoride, and concen- x-rays with maximum intensity is: trated sulfuric acid. See boron trichloride. nλ = 2dsinθ where θ is the angle of incidence and re- borosilicates /bor-ŏ-sil-ă-kayts/ Com- flection (Bragg angle) that the x-rays make plex compounds similar to silicates, but with the crystal planes, n is a small integer, λ containing BO3 and BO4 units in addition is the wavelength of the x-rays, and d is to the SiO4 units. Certain crystalline the distance between the crystal planes. borosilicate minerals are known. In addi- The equation is named for the British tion, borosilicate glasses can be made by physicist Sir William Lawrence Bragg using boron oxide in addition to (1890–1971). silicon(IV) oxide. These tend to be tougher and more heat resistant than ‘normal’ sili- branched chain See chain. cate glass. brass Any of a group of copper–zinc al- Bosch process /bosh/ The reaction loys containing up to 50% of zinc. The → CO + H2O CO2 + H2 color of brass changes from red-gold to using water gas over a hot catalyst. It has golden to silvery-white with increasing zinc been used to make hydrogen for the Haber content. Brasses are easy to work and resist process. The process is named for the Ger- corrosion well. Brasses with up to 35% man industrial chemist Carl Bosch zinc can be worked cold and are specially (1874–1940). suited for rolling into sheets, drawing into

42 bromoethane wire, and making into tubes. Brasses with ganese dioxide. Industrial methods of pro- 35–46% zinc are harder and stronger but duction utilize oxidation by chlorine or less ductile; they require hot working (e.g. electrolysis with removal from the solution forging). The properties of brass can be im- by purging with air. Bromine and its com- proved by the addition of other elements; pounds are used in pharmaceuticals, pho- lead improves its ability to be machined, tography, chemical synthesis, fumigants, while aluminum and tin increase its corro- and in significantly large quantities as 1,2- sion resistance. See also bronze; nickel–sil- dibromoethane (which is added to gasoline ver. to combine with lead produced from the decomposition of the antiknock agent lead bremsstrahlung /brem-shtrah-lûng/ See tetraethyl). x-radiation. The electropositive elements form ionic bromides and the non-metals form fully brine A concentrated solution of sodium covalent bromides. Like chlorine, bromine chloride. forms oxides, Br2O and BrO2, both of which are unstable. The related oxo-acid Brin process See barium. anions hypobromite (BrO–) and bromate – (BrO3 ) are formed by the reaction of bromic(I) acid /broh-mik/ (hypobromous bromine with cold aqueous alkali and hot acid; HBrO) A pale yellow liquid made aqueous alkali respectively, but the by reacting mercury(II) oxide with bromine analogs of chlorite and perchlo- bromine water. It has strong bleaching rate are not known. powers. Bromic(I) acid will donate protons Bromine and the interhalogens are to only a small extent and hence is a weak highly toxic. Liquid bromine and bromine acid in aqueous solution. It is a strong oxi- solutions are also very corrosive and gog- dizing agent. See also bromine water. gles and gloves should always be worn when handling such compounds. bromic(V) acid (HBrO ) A colorless 3 Symbol: Br; m.p. –7.25°C; b.p. liquid made by the addition of dilute sulfu- ° ° ric acid to barium bromate. It dissociates 58.78 C; r.d. 3.12 (20 C); p.n. 35; r.a.m. extensively in aqueous solution and is a 79.904. strong acid. bromine trifluoride (BrF3) A colorless bromide /broh-mÿd/ See halide. fuming liquid made by direct combination of fluorine and bromine. It is a very reac- bromination /broh-mă-nay-shŏn/ See tive compound, its reactions being similar halogenation. to those of its component halides. bromine /broh-meen, -min/ A deep red, bromine water A yellow solution of moderately reactive element belonging to bromine in water, which contains the halogens; i.e. group 17 (formerly VIIA) bromic(I) acid (hypobromous acid, HBrO). of the periodic table. Bromine is a liquid at It is a weak acid and a strong oxidizing room temperature (mercury is the only agent, and decomposes to give a mixture of – – other element with this property). It occurs bromide (Br ) and bromate(V) (BrO3 ) in small amounts in seawater, salt lakes, ions. and salt deposits but is much less abundant than chlorine. Bromine reacts with most bromobutyl /broh-moh-byoo-t’l/ See metals but generally with less vigor than butyl rubber. chlorine. It has less oxidizing power than chlorine and consequently can be released bromoethane /broh-moh-eth-ayn/ (ethyl from solutions of bromides by reaction bromide; C2H5Br) A colorless volatile with chlorine gas. The laboratory method compound, used as a refrigerant. It can be is the more convenient oxidation by man- made from ethene and hydrogen bromide.

43 bromoform bromoform /broh-mŏ-form/ See tribro- [Fe(NO)]SO4, which breaks down on momethane. shaking. bromomethane /broh-moh-meth-ayn/ buckminsterfullerene /buk-min-ster-fûl- (methyl bromide; CH3Br) A colorless ĕ-reen/ An allotrope of carbon contain- volatile compound used as a solvent. It can ing clusters of 60 carbon atoms bound in a be made from methane and bromine. highly symmetric polyhedral structure. The C60 polyhedron has a combination of pen- Brønsted–Lowry theory /bron-sted low- tagonal and hexagonal faces similar to the ree/ See acid. panels on a soccer ball. The molecule was named for the American architect Richard bronze Any of a group of copper-tin al- Buckminster Fuller (1895–1983) because loys usually containing 0.5–10% of tin. its structure resembles a geodesic dome (in- They are generally harder, stronger in com- vented by Fuller). The C60 polyhedra are pression, and more corrosion resistant informally called bucky balls. The original than brass. Zinc is often added, as in gun- method of making the allotrope was to fire metal (2–4% zinc), to increase strength a high-power laser at a graphite target. and corrosion-resistance; bronze coins This also produces less stable carbon clus- often contain more zinc (2.5%) than tin ters, such as C70. It can be produced more (0.5%). The presence of lead improves its conveniently using an electric arc between machining qualities. graphite electrodes in an inert gas. The al- Some copper-rich alloys containing no lotrope is soluble in benzene, from which it tin are also called bronzes. Aluminum can be crystallized to give yellow crystals. This form of carbon is also known as ful- bronzes, for example, with up to 10% alu- lerite. minum, are strong, resistant to corrosion The discovery of buckminsterfullerene and wear, and can be worked cold or hot; led to a considerable amount of research silicon bronzes, with 1–5% silicon, have into its properties and compounds. Partic- high corrosion-resistance; beryllium ular interest has been shown in trapping bronzes, with about 2% beryllium, are metal ions inside the carbon cage to form very hard and strong. enclosure compounds. Buckminster- fullerene itself is often simply called brown coal See lignite. fullerene. The term also applies to derivatives of buckminsterfullerene and to simi- Brownian movement (Brownian motion) The random motion of small particles in a fluid – for example, smoke particles in air. The particles, which may be large enough to be visible with a microscope, move because they are continuously bombarded by the molecules of the fluid. Brownian movement is named for the Scot- tish botanist Robert Brown (1773–1858). brown-ring test A qualitative test used for the detection of nitrate. A freshly prepared solution of iron(II) sulfate is mixed with the sample and concentrated sulfuric acid is introduced slowly to the bottom of the tube using a dropping pipette so that two layers are formed. A brown ring formed where the liquids meet indicates the presence of nitrate. The brown color is Buckminsterfullerene

44 butanoic acid lar cluster (e.g. C70). Carbon structures Bunsen cell A type of primary cell in similar to that in C60 can also form small which the positive electrode is formed by tubes, known as bucky tubes. carbon plates in a nitric acid solution and the negative electrode consists of zinc bucky ball /buk-ee/ See buckminster- plates in sulfuric acid solution. fullerene. buret /byû-ret/ A piece of apparatus bucky tube See buckminsterfullerene. used for the addition of variable volumes of liquid in a controlled and measurable buffer A solution in which the pH re- way. The buret is a long cylindrical gradu- mains reasonably constant when acids or ated tube of uniform bore fitted with a alkalis are added to it; i.e. it acts as a buffer stopcock and a small-bore exit jet, en- against (small) changes in pH. Buffer solu- abling a drop of liquid at a time to be tions generally contain a weak acid and added to a reaction vessel. Burets are one of its salts derived from a strong base; widely used for titrations in volumetric e.g. a solution of ethanoic acid and sodium analysis. Standard burets permit volume ethanoate. If an acid is added, the H+ reacts measurement to 0.005 cm3 and have a total with the ethanoate ion (from dissociated capacity of 50 cm3; a variety of smaller mi- sodium ethanoate) to form undissociated croburettes is available. Similar devices are ethanoic acid; if a base is added the OH– used to introduce measured volumes of gas reacts with the ethanoic acid to form water at regulated pressure in the investigation of and the ethanoate ion. The effectiveness of gas reactions. the buffering action is determined by the concentrations of the acid–anion pair: buta-1,3-diene /byoo-tă dÿ-een/ (butadi- + – K = [H ][CH3COO ]/[CH3COOH] ene; CH2:CHCH:CH2) A colorless gas where K is the dissociation constant. made by catalytic dehydrogenation of bu- Phosphate, oxalate, tartrate, borate, tane. It is used in the manufacture of syn- and carbonate systems can also be used for thetic rubber. Buta-1,3-diene is conjugated buffer solutions. and to some extent the pi electrons are delocalized over the whole of the molecule. bumping Violent boiling of a liquid caused when bubbles form at a pressure butanal /byoo-tă-nal/ (butyraldehyde; above atmospheric pressure. C3H7CHO) A colorless liquid aldehyde.

Bunsen burner /bun-sĕn/ A gas burner butane /byoo-tayn, byoo-tayn/ (C4H10) consisting of a vertical metal tube with an A gaseous alkane obtained either from the adjustable air-inlet hole at the bottom. Gas gaseous fraction of crude oil or by the is allowed into the bottom of the tube and ‘cracking’ of heavier fractions. Butane is the gas–air mixture is burnt at the top. easily liquefied and its main use is as a With too little air the flame is yellow and portable supply of fuel (bottle gas). sooty. Correctly adjusted, the burner gives Butane is the fourth member of the ho- a flame with a pale blue inner cone of in- mologous series of alkanes. completely burnt gas, and an almost invis- ible outer flame where the gas is fully butanedioic acid /byoo-tayn-dÿ-oh-ik/ oxidized and reaches a temperature of (succinic acid) A crystalline carboxylic ° about 1500 C. The inner region is the re- acid, HOOC(CH2)2COOH, that occurs in ducing part of the flame and the outer re- amber and certain plants. It forms during gion the oxidizing part (see borax-bead the fermentation of sugar (sucrose). test). The Bunsen burner is named for the German chemist Wilhelm Bunsen butanoic acid /byoo-tă-noh-ik/ (butyric (1811–99). He did not invent the Bunsen acid; C3H7COOH) A colorless liquid burner, but used it to great effect in pio- carboxylic acid. Esters of butanoic acid are neering work on spectroscopy. present in butter.

45 butanols butanols /byoo-tă-nolz, -nohlz/ (butyl al- H CO.OH cohols; C4H9OH) Two alcohols that are derived from butane: the primary alcohol C butan-1-ol (CH3(CH2)2CH2OH) and the secondary alcohol butan-2-ol (CH3CH(OH)CH2CH3). Both are color- C less volatile liquids used as solvents. H CO.OH cis (maleic) butanone /byoo-tă-nohn/ (methyl ethyl ketone; CH3COC2H5) A colorless volatile liquid ketone. It is manufactured by the oxidation of butane and used as a HO.OC H solvent. C butenedioic acid /byoo-teen-dÿ-oh- ik/ Either of two isomers. Transbutene- C dioic acid (fumaric acid) is a crystalline H CO.OH compound found in certain plants. Cis- butenedioic acid (maleic acid) is used in the trans (fumaric) manufacture of synthetic resins. It can be Butenedioic acids converted into the trans isomer by heating at 120°C. the inner surface of the tire. Other uses are in sealants, hoses, and pond liners. butyl alcohol /byoo-t’l/ See butanols. butyraldehyde /byoo-t’l-al-dĕ-hÿd/ See butyl group The straight chain alkyl butanal. group CH3(CH2)2CH2–. butyric acid /byoo-ti-rik/ See butanoic butyl rubber A type of synthetic rubber acid. made by copolymerizing isobutylene (2- methylpropene, CH3:C(CH3)2) with small by-product A substance obtained dur- amounts of isoprene (methylbuta-1,3- ing the manufacture of a main chemical diene, CH3:C(CH3)CH:CH2). product. For example, propanone is not Before the introduction of tubeless tires now manufactured from propan-1-ol, but butyl rubber was used for inner tubes be- is obtained as a by-product in the manu- cause it is impervious to air. Subsequently facture of phenol by the cumene process. halogenated butyl rubbers were developed Calcium chloride is a by-product of the (halobutyls), which could be cured at Solvay process for making sodium carbon- higher temperature and vulcanized with ate. Some metals are obtained as by-prod- other rubbers. Both chlorobutyls and bro- ucts in processes to extract other metals. mobutyls are manufactured. These types of Cadmium, for instance, is a by-product of rubber are used in tubeless tires bonded to the extraction of zinc.

46 C

cadmium /kad-mee-ŭm/ A transition calcium /kal-see-ŭm/ A moderately soft, metal obtained as a by-product during the low-melting reactive metal; the third ele- extraction of zinc. It is used to protect ment in group 2 (formerly IIA) of the peri- other metals from corrosion, as a neutron odic table. The electronic configuration is absorber in nuclear reactors, in alkali bat- that of argon with an additional pair of 4s teries, and in certain pigments. It is highly electrons. toxic. Calcium is widely distributed in the Symbol: Cd; m.p. 320.95°C; b.p. Earth’s crust and is the third most abun- 765°C; r.d. 8.65 (20°C); p.n. 48; r.a.m. dant element. Large deposits occur as 112.411. chalk or marble, CaCO3; gypsum, CaSO4. 2H2O; anhydrite, CaSO4; fluorspar, CaF; cadmium cell See Weston cadmium and apatite, CaF2.Ca3(PO4)3. However cell. sufficiently large quantities of calcium chloride are available as waste from the caesium /see-zee-ŭm, see-see-/ See ce- Solvay process to satisfy industrial require- sium. ments for the metal, which is produced by electrolysis of the fused salt. Large quanti- cage compounds See clathrate. ties of lime, Ca(OH)2, and quicklime, CaO, are produced by decomposition of calamine /kal-ă-mÿn, -min/ 1. A mineral the carbonate for use in both building and consisting of hydrated zinc silicate (2ZnO. agriculture. Several calcium minerals are SiO2.H2O). It is also known as hemi- mined as a source of other substances. morphite. Thus, limestone is a cheap source of carbon 2. Zinc carbonate (ZnCO3), which occurs dioxide, gypsum and anhydrite are used in naturally as a mineral also known as smith- the manufacture of sulfuric acid, phos- sonite. The carbonate is used medicinally phate rock for phosphoric acid, and in suspension as a soothing lotion for sun- fluorspar for a range of fluorochemicals. burn and skin complaints. Formerly, the Calcium has a low ionization potential natural mineral was used for this but now and a relatively large atomic radius. It is medicinal calamine is made by precipitat- therefore a very electropositive element. ing a basic zinc carbonate from a solution The metal is very reactive and the com- of a zinc salt. It is usually colored pink by pounds contain the divalent ion Ca2+. Cal- the addition of small quantities of iron(III) cium forms the oxide (CaO), a white ionic oxide. solid, on burning in air, but for practical purposes the oxide is best prepared by calcination /kal-să-nay-shŏn/ The for- heating the carbonate, which decomposes mation of a calcium carbonate deposit at about 800°C. Both the oxide and the from hard water. metal itself react with water to give the basic hydroxide (Ca(OH)2). On heating calcite /kal-sÿt/ A mineral form of cal- with nitrogen, sulfur, or the halogens, calcium carbonate occurring in limestone, cium reacts to form the nitride (Ca3N2), chalk, and marble. sulfide (CaS), or the halides (CaX2). Cal- 47 calcium acetylide cium also reacts directly with hydrogen to izer because ammonia and calcium carbon- give the hydride CaH2 and borides, arate are slowly formed when water is added: → senides, carbides, and silicides can be pre- CaCN2 + 3H2O CaCO3 + 2NH3 pared in a similar way. Both the carbonate Other uses include the defoliation of cot- and sulfate are insoluble. Calcium salts im- ton plants and the production of part a characteristic brick-red color to melamine. flames which is an aid to qualitative analysis. At ordinary temperatures calcium has calcium dicarbide (calcium acetylide; cal- the face-centered cubic structure with a cium carbide; CaC2) A colorless solid transition at 450°C to the close-packed when pure. In countries where electricity is hexagonal structure. cheap, calcium dicarbide is produced on a Symbol: Ca; m.p. 839°C; b.p. 1484°C; large scale by heating calcium oxide with r.d. 1.55 (20°C); p.n. 20; r.a.m. 40.0878. coke at a temperature in excess of 2000°C in an electric-arc furnace. Water is then calcium acetylide See calcium dicar- added to give ETHYNE (C2H2), an important bide. industrial organic chemical: → CaC2 + 2H2O C2H2 + Ca(OH)2 calcium bicarbonate See calcium hy- The structure of calcium dicarbide is in- drogencarbonate. teresting because the carbon is present as 2– carbide ions (C2 ). calcium carbide See calcium dicarbide. calcium fluoride (CaF2) A white crys- calcium carbonate (CaCO3) A white talline compound found naturally as fluo- solid that occurs naturally in two crys- rite (fluorspar). talline forms: calcite and aragonite. These minerals make up the bulk of such rocks as calcium-fluoride structure (fluorite marble, limestone, and chalk. Calcium car- structure) A form of crystal structure in bonate also occurs in the mineral dolomite which each calcium ion is surrounded by (CaCO3.MgCO3). It is sparingly soluble in eight fluorine ions arranged at the corners water but dissolves in rainwater containing of a cube and each fluorine ion is sur- carbon dioxide to form calcium hydrogen- rounded tetrahedrally by four calcium carbonate, which causes temporary hard- ions. ness of water. Calcium carbonate is a basic raw material in the Solvay process and is calcium hydrogencarbonate (calcium used for making glass, mortar, and cement. bicarbonate, Ca(HCO3)2) A solid formed when water containing carbon dioxide dis- calcium chloride (CaCl2) A white solid solves calcium carbonate: → that occurs in a number of hydrated forms CaCO3 + H2O + CO2 Ca(HCO3)2 and is readily available as a by-product of Calcium hydrogencarbonate is a cause of the Solvay process. It is readily soluble in temporary hard water. The solid is un- water and the solution, known as brine, is known at room temperature. See hardness. used in refrigerating plants. Other applications that depend on its water-absorbing calcium hydroxide (slaked lime; property and the low freezing point of the Ca(OH)2) A white solid that dissolves aqueous solution include the suppression sparingly in water to give the alkali known of dust on roads and in mines and the melt- as limewater. Calcium hydroxide is manu- ing of snow. Calcium chloride is used as the factured by adding water to the oxide, a electrolyte in the production of calcium. process known as slaking, which evolves much heat. If just sufficient water is added calcium cyanamide (CaCN2) A solid so that the oxide turns to a fine powder, prepared by heating calcium dicarbide to a the product is slaked lime. If more water is temperature in excess of 800°C in an at- added, a thick suspension called milk of mosphere of nitrogen. It is used as a fertil- lime is formed. Calcium hydroxide has

48 calomel electrode many uses. As a base, it is used to neutral- component of the slag produced in smelt- ize acid soil and in industrial processes ing iron and other metals in a blast furnace. such as the Solvay process. It is also used in the manufacture of mortar, whitewash, calcium stearate See calcium octade- and bleaching powder and for the soften- canoate. ing of temporary hard water. calcium sulfate (anhydrite; CaSO4)A calcium nitrate (Ca(NO3)2) A deliques- white solid that occurs abundantly as the cent salt that is very soluble in water. It is mineral anhydrite and as the dihydrate usually crystallized as the tetrahydrate (CaSO4.2H2O), known as gypsum or alabaster. When heated, gypsum loses water Ca(NO3)2.4H2O. When the hydrate is heated, the anhydrous salt is first produced to form the hemihydrate (2CaSO4.H2O), and this subsequently decomposes to give which is plaster of Paris. If the water is re- calcium oxide, nitrogen dioxide, and oxy- placed, gypsum reforms and sets as a solid. gen. Calcium nitrate is used as a nitroge- Plaster of Paris is therefore used for taking nous fertilizer. casts and for setting broken limbs. Calcium sulfate is sparingly soluble in water and is calcium octadecanoate /ok-tă-dek-ă- a cause of permanent hardness in water. It noh-ayt/ (calcium stearate; Ca(CH (CH ) - is used in ceramics, paint, and in paper 3 2 16 making. COO)2) An insoluble salt of octadecanoic acid. It is formed as ‘scum’ when SOAP, con- kal-gon taining the soluble salt sodium octade- Calgon / / (Trademark) A substance often added to detergents to remove canoate, is mixed with hard water unwanted chemicals that have dissolved in containing calcium ions. water and would otherwise react with soap to form a scum. Calgon consists of compli- calcium oxide (quicklime; CaO) A cated polyphosphate molecules, which ab- white solid formed by heating calcium in sorb dissolved calcium and magnesium oxygen or, more widely, by the thermal de- ions. The metal ions become trapped composition of calcium carbonate. On a within the Calgon molecules. large scale, limestone (calcium carbonate) is heated in a tall tower called a lime kiln to kah-lee-chay ° caliche / / An impure com- a temperature of 550 C. The reversible re- mercial form of sodium nitrate. action: ˆ CaCO3 CaO + CO2 californium /kal-ă-for-nee-ŭm/ A sil- proceeds in a forward direction as the car- very radioactive transuranic element of the bon dioxide is carried away by the upward actinoid series of metals, not found natu- current through the kiln. Calcium oxide is rally on Earth. Several radioisotopes have used in extractive metallurgy to produce a been synthesized, including californium- slag with the impurities in metal ores; it is 252, which is used as an intense source of also used as a drying agent and it is an in- neutrons in certain types of portable detec- termediate for the production of calcium tor and in the treatment of cancer. hydroxide. Symbol: Cf; m.p. 900°C; p.n. 98; most stable isotope 251Cf (half-life 900 years). calcium phosphate (Ca3(PO4)2)A solid that occurs naturally in the mineral calixarene /kă-liks-ă-reen/ See host– apatite (CaF2.Ca3(PO4)3) and in rock phos- guest chemistry. phate. It is the chief constituent of animal bones and is used extensively in fertilizers. calomel /kal-ŏ-mel/ See mercury(I) chloride. calcium silicate (Ca2SiO4) A white insoluble crystalline compound found in var- calomel electrode A half cell having a ious cements and minerals. It is also a mercury electrode coated with mercury(I)

49 calorie chloride (called calomel), in an electrolyte cane sugar See sucrose. consisting of potassium chloride and (saturated) mercury(I) chloride solution. Its Cannizzaro reaction /kahn-need-dzah- standard electrode potential against the hy- roh/ The reaction of aldehydes to give al- drogen electrode is accurately known cohols and acid anions in the presence of (–0.2415 V at 25°C) and it is a convenient strong bases. The aldehydes taking part in secondary standard. the Cannizzaro reaction lack hydrogen atoms on the carbon attached to the alde- calorie /kal-ŏ-ree/ Symbol: cal A unit of hyde group. For instance, in the presence of energy approximately equal to 4.2 joules. hot aqueous sodium hydroxide: It was formerly defined as the energy → NaOH + 2C6H5CHO needed to raise the temperature of one – + C6H5CH2OH + C6H5COO Na gram of water by one degree Celsius. Be- This reaction is a disproportionation, in- cause the specific thermal capacity of water volving both oxidation (to acid) and reduc- changes with temperature, this definition is tion (to alcohol). It can also occur with not precise. The mean or thermochemical methanal to give methanol and meth- calorie (calTH) is defined as 4.184 joules. anoate ions. The international table calorie (calIT) is de- → NaOH + 2HCHO CH3OH + fined as 4.1868 joules. Formerly the mean HCOO–Na+ calorie was defined as one hundredth of the The reaction is named for the Italian heat needed to raise one gram of water chemist Stanislao Cannizzaro (1826–1910) from 0°C to 100°C, and the 15°C calorie who first described it in 1853. as the heat needed to raise it from 14.5°C to 15.5°C. canonical form See resonance. calorific value /kal-ŏ-rif-ik/ The energy caproic acid /kă-proh-ik/ See hexanoic content of a fuel, defined as the energy re- acid. leased in burning unit mass of the fuel. caprolactam /kap-roh-lak-tăm/ (C H NO) calorimeter /kal-ŏ-rim-ĕ-ter/ A device or 6 11 apparatus for measuring thermal proper- A white crystalline substance used in the ties such as specific heat capacity, calorific manufacture of NYLON. value, etc. See bomb calorimeter. caprylic acid /kă-pril-ik/ See octanoic calx /kal’ks/ A metal oxide obtained by acid. heating an ore to high temperatures in air. carbamide /kar-bă-mÿd, -mid, kar-bam- ÿd, -id/ See urea. camphor /kam-fer/ (C10H16O) A naturally-occurring white organic compound with a characteristic penetrating odor. It is carbanion /kar-ban-ÿ-ŏn, -on/ An inter- a cyclic compound and a ketone, formerly mediate in an organic reaction in which obtained from the wood of the camphor one carbon atom is electron-rich and car- tree but now made synthetically. Camphor ries a negative charge. Carbanions are usu- is used as a platicizer for celluloid and as an ally formed by abstracting a hydrogen ion insecticide against clothes moths. from a C–H bond using a base, e.g. from – ethanal to form CH2CHO, or from candela Symbol: cd The SI base unit of organometallic compounds in which the luminous intensity, defined as the intensity carbon atom is bonded to an electroposi- (in the perpendicular direction) of the tive metal. black-body radiation from a surface of 1/600 000 square meter at the temperature carbazole /kar-bă-zohl/ (C12H9N) A of freezing platinum and at a pressure of white crystalline compound used in the 101 325 pascals. manufacture of dyestuffs.

50 carbohydrates carbene /kar-been/ A transient species of Ni3C) have properties intermediate be- the form RR′C:, with two valence electrons tween those of interstitial and ionic car- that do not form bonds. The simplest ex- bides. ample is methylene, H2C:. Carbenes are short-lived intermediates in some organic carbocation An ion with a positive reactions. They attack double bonds to charge in which the charge is mostly local- form three-membered rings (i.e. cyclo- ized on a carbon atom. There are two propane derivatives). They also attack sin- types. Carbonium ions have five bonds to gle bonds in insertion reactions, for the carbon atom and a complete outer shell example: of 8 electrons. The simplest example would → be the carbonium ion CH +, which could R–O–H + R2C: R–O–C(R2)H 5 → be regarded as formed by adding H+ to R–H + R2C: R–C(R2)–H Carbenes are important ‘reagents’ in or- methane, CH4, in the same way that the + ganic synthesis and various methods exist ammonium ion, NH4 , is formed from am- for generating them in the reaction monia, NH3. There is, however, a differ- medium. ence between ammonia and methane in that ammonia has a lone pair of electrons, + carbenium ion /kar-bee-nee-ŭm/ See which it can donate in forming the NH4 + carbocation. ion. The carbonium ion CH5 (and similar ions) is a transient species, produced in the carbide /kar-bÿd/ A compound of car- gas phase by electron bombardment of or- bon with a more electropositive element. ganic compounds and detected in a mass The carbides of the elements are classified spectrum. Its shape is that of a carbon atom with three hydrogens in a plane and into: one hydrogen above and one below (a trig- 1. Ionic carbides, which contain the car- onal bipyramid). bide ion C4–. An example is aluminum Carbenium ions have three bonds to the carbide, Al C . Compounds of this type 4 3 central carbon and are planar, with the react with water to give methane (they bonds directed toward the corners of a tri- were formerly also called methanides). angle (sp2 hybridization). They have six The dicarbides are ionic carbon com- electrons in outer shell of carbon and a va- pounds that contain the dicarbide ion – – cant p orbital. Carbenium ions are impor- C:C . The best-known example is cal- tant intermediates in a number of organic cium dicarbide, CaC2, also known as reactions, notably the S 1 mechanism of calcium carbide, or simply carbide. N NUCLEOPHILIC SUBSTITUTION. It is possible to Compounds of this type give ethyne produce stable carbenium ions in salts of with water. They were formerly called + – the type (C6H5)3C Cl , which are orange- acetylides or ethynides. Ionic carbides red solids. In these the triphenylmethyl are formed with very electropositive cation is stabilized by delocalization over metals. They are crystalline. the three phenyl groups. It is also possible 2. Covalent carbides, which have giant- to produce carbenium ions using SU- molecular structures, as in silicon car- PERACIDS. bide (SiC) and boron carbide (B4C3). These are hard high-melting solids. carbocyclic compound /kar-boh-sÿ-klik, Other covalent compounds of carbon -sik-lik/ A compound, such as benzene or (CO2, CS2, CH4, etc.) have covalent cyclohexane, that contains a ring of carbon molecules. atoms in its structure. 3. Interstitial carbides, which are interstitial compounds of carbon with transi- carbohydrates /kar-boh-hÿ-dayts/A tion metals. Titanium carbide (TiC) is an class of compounds occurring widely in na- example. These compounds are all hard ture and having the general formula type high-melting solids, with metallic prop- Cx(H2O)y. (Note that although the name erties. Some carbides (e.g. nickel carbide suggests a hydrate of carbon these com-

51 carbolic acid

Graphite

Diamond

Carbon structures pounds are in no way hydrates and have no tities using the Acheson process in which similarities to classes of hydrates.) Carbo- coke and small amounts of asphalt or clay hydrates are generally divided into two are raised to high temperatures. Large main classes: SUGARS and POLYSACCHA- quantities of impure carbon are also con- RIDES. sumed in the reductive extraction of met- Carbohydrates are both stores of en- als. Apart from the demand for diamond as ergy and structural elements in living sys- a gemstone there is a large industrial de- tems; plants having typically 15% mand for low-grade small diamonds for carbohydrate and animals about 1% car- drilling and grinding machinery. High- bohydrate. The body is able to build up temperature studies show that graphite polysaccharides from simple units (an- and diamond can be inter-converted at abolism) or break the larger units down to 3000°C and extremely high pressures but more simple units for releasing energy (ca- the commercial exploitation would not be tabolism). viable. Carbon burns in oxygen to form carbon carbolic acid /kar-bol-ik/ A former dioxide and carbon monoxide, CO. Car- name for phenol (hydroxybenzene, bon dioxide is soluble in water forming the C6H5OH). weakly acidic carbonic acid, the parent acid of the metal carbonates. In contrast carbon /kar-bŏn/ The first element of CO is barely soluble in water but it will group 14 (formerly IVA) of the periodic react with alkali to give the methanoate table. Carbon is a universal constituent of (formate) ion: – → – living matter and the principal deposits of CO + OH HCO2 carbon compounds are derived from living Carbon will react readily with sulfur at sources; i.e., carbonates (chalk and lime- red heat to form CS2 but it does not react stone) and fossil fuels (coal, oil, and gas). It directly with nitrogen. Cyanogen, (CN)2, also occurs in the mineral dolomite. The el- must be prepared by heating covalent ement forms only 0.032% by mass of the metal cyanides such as CuCN. Carbon will Earth’s crust. Minute quantities of elemen- also react directly with many metals at ele- tal carbon also occur as the allotropes vated temperatures to give carbides. Car- graphite and diamond. A third allotrope, bides can also be obtained by heating the buckminsterfullerene (C60), also exists. metal oxide with carbon or heating the The industrial demand for graphite is metal with a hydrocarbon. There is a be- such that it is manufactured in large quan- wilderingly wide range of metal carbides,

52 carbon disulfide both salt-like with electropositive elements which are burned, again with a formation (CaC2) and covalent with the metalloids of carbon dioxide. (SiC), and there are also many interstitial carbides formed with metals such as Cr, carbon dating (radiocarbon dating)A Mn, Fe, Co, and Ni. method of dating – measuring the age of The compounds with C–N bonds form (usually archaeological) materials that con- a significant branch of inorganic chemistry tain matter of living origin. It is based on of carbon, these are hydrogen cyanide the fact that 14C, a beta emitter of half-life (HCN) and the cyanides, cyanic acid approximately 5730 years, is being formed (HNCO) and the cyanates, and thiocyanic continuously in the atmosphere as a result acid (HNCS) and the thiocyanates. of cosmic-ray action. Naturally occurring carbon has the iso- The 14C becomes incorporated into liv- topic composition 12C (98.89%), 13C ing organisms. After death of the organism (1.11%) and 14C (minute traces in the the amount of radioactive carbon de- upper atmosphere produced by slow neu- creases exponentially by radioactive decay. tron capture by 14N atoms). 14C is used for The ratio of 12C to 14C is thus a measure of radiocarbon dating because of its long the time elapsed since the death of the or- half-life of 5730 years. ganic material. Symbol: C; m.p. 3550°C; b.p. 4830°C The method is most valuable for speci- ° (sublimes); C60 sublimes at 530 C; r.d. mens of up to 20 000 years old, though it 3.51 (diamond), 2.26 (graphite), 1.65 (C60) has been modified to measure ages up to (all at 20°C); p.n. 6; r.a.m. 12.011. 70 000 years. For ages of up to about 8000 See also buckminsterfullerene. years the carbon time scale has been cali- brated by dendrochronology; i.e. by mea- carbonate /kar-bŏ-nayt, -nit/ A salt of suring the 12C:14C ratio in tree rings of 2– carbonic acid (containing the ion CO3 ). known antiquity. carbonation /kar-bŏ-nay-shŏn/ 1. The carbon dioxide /dÿ-oks-ÿd, -id/ (CO2) solution of carbon dioxide in a liquid A colorless odorless nonflammable gas under pressure, as in carbonated soft formed when carbon burns in excess oxy- drinks. gen. It is also produced by respiration. Car- 2. The addition of carbon dioxide to com- bon dioxide is present in the atmosphere pounds, e.g. the insertion of carbon diox- (0.03% by volume) and is converted in ide into Grignard reagents. plants to carbohydrates by photosynthesis. In the laboratory it is made by the action of carbon black A finely divided form of dilute acid on metal carbonates. Industri- carbon produced by the incomplete com- ally, it is obtained as a by-product in cer- bustion of such hydrocarbon fuels as nat- tain processes, such as fermentation or the ural gas or petroleum oil. It is used as a manufacture of lime. The main uses are as black pigment in inks and as a filler for a refrigerant (solid carbon dioxide, called rubber in tire manufacture. dry ice) and in fire extinguishers and carbonated drinks. Increased levels of carbon carbon cycle The circulation of carbon dioxide in the atmosphere from the com- compounds in the environment, one of the bustion of fossil fuels are thought to con- major natural cycles of an element. Carbon tribute to the greenhouse effect. dioxide in the air is used by green plants in Carbon dioxide is the anhydride of the photosynthesis (in which it is combined weak acid carbonic acid, which is formed with water to form sugars and starches). in water: → Plants are eaten by animals which exhale CO2 + H2O H2CO3 carbon dioxide, or when plants and animals die their remains decompose with the carbon disulfide (CS2) A colorless poi- production of carbon dioxide. Some plants sonous flammable liquid made from are burned or converted to fossil fuels methane (natural gas) and sulfur. It is a sol-

53 carbon fibers vent. The pure compound is virtually odor- carbonyl /kar-bŏ-nil/ A complex in less, but CS2 usually has a revolting smell which carbon monoxide ligands are coor- because of the presence of other sulfur dinated to a metal atom. A common exam- compounds. ple is tetracarbonyl nickel(0), Ni(CO)4. carbon fibers Fibers of graphite, which carbonyl chloride (phosgene; are used, for instance, to strengthen poly- COCl2) A colorless toxic gas with a mers. They are made by heating stretched choking smell. It is used as a chlorinating textile fibers and have an orientated crystal agent and to make polyurethane plastics structure. and insecticides; it was formerly employed as a war gas. carbonic acid /kar-bon-ik/ (H CO )A 2 3 carbonyl group The group –C=O. It dibasic acid formed in small amounts in so- occurs in aldehydes (RCO.H), ketones lution when carbon dioxide dissolves in (RR′CO), carboxylic acids (RCO.OH), water: ˆ and in carbonyl complexes of transition CO2 + H2O H2CO2 metals. It forms two series of salts: hydrogencar- – 2– bonates (HCO3 ) and carbonates (CO3 ). carborundum /kar-bŏ-run-dŭm/ See sil- The pure acid cannot be isolated. icon carbide. carbonium ion /kar-boh-nee-ŭm/ See carboxylate ion /kar-boks-ă-layt/ The carbocation. ion –COO–, produced by ionization of a carboxyl group. In a carboxylate ion the carbonize /kar-bŏ-nÿz/ (carburize)To negative charge is generally delocalized convert an organic compound into carbon over the O–C–O grouping and the two by incomplete oxidation at high tempera- C–O bonds have the same length, interme- ture. diate between that of a double C=O and a single C–O. carbon monoxide /mon-oks-ÿd, -id/ (CO) A colorless flammable toxic gas carboxyl group /kar-boks-ăl/ The or- formed by the incomplete combustion of ganic group –CO.OH, present in car- carbon. In the laboratory it can be made by boxylic acids. dehydrating methanoic acid with concentrated sulfuric acid: carboxylic acid /kar-boks-il-ik/ A type → of organic compound with the general for- HCOOH – H2O CO Industrially, it is produced by the oxida- mula RCOOH. Many carboxylic acids tion of carbon or of natural gas, or by the occur naturally in plants and (in the form of esters) in fats and oils, hence the alter- water-gas reaction. It is a powerful reduc- native name fatty acids. Carboxylic acids ing agent and is used in metallurgy. with one COOH group are called monoba- Carbon monoxide is neutral and only sic, those with two, dibasic, and those with sparingly soluble in water. It is not the anhydride of methanoic acid, although under extreme conditions it can react with sodium hydroxide to form sodium methanoate. It forms metal carbonyls with O transition metals, and its toxicity is due to its ability to form a complex with hemoglobin. C R OH carbon tetrachloride /tet-ră-klor-ÿd, -id, -kloh-rÿd, -rid/ See tetrachloromethane. Carboxylic acid

54 cast iron three, tribasic. The methods of preparation pressure, volume, and temperature, and are: transfers energy to or from mechanical 1. Oxidation of a primary alcohol or an work. The efficiency of the Carnot cycle is aldehyde: the maximum attainable in a heat engine. → RCH2OH + 2[O] RCOOH + H2O The cycle is named for the French physicist 2. Hydrolysis of a nitrile using dilute hy- Nicolas Leonard Sadi Carnot (1796– drochloric acid: 1832). See Carnot’s principle. → RCN + HCl + 2H2O RCOOH + NH4Cl Carnot’s principle (Carnot theorem) The acidic properties of carboxylic The efficiency of any heat engine cannot be acids are due to the carbonyl group, which greater than that of a reversible heat engine attracts electrons from the C–O and O–H operating over the same temperature bonds. The carboxylate ion formed, range. It follows directly from the second R–COO–, is also stabilized by delocaliza- law of thermodynamics, and means that all tion of electrons over the O–C–O group- reversible heat engines have the same effi- ing. ciency, independent of the working sub- Other reactions of carboxylic acids instance. If heat is absorbed at temperature clude the formation of esters and the reac- T1 and given out at T2, then the Carnot ef- tion with phosphorus(V) chloride to form ficiency is (T1 – T2)/T1. acyl halides. Caro’s acid /kah-roh/ See peroxosulfu- carburizing /kar-bŭ-rÿz, -byŭ-/ See case ric(VI) acid. hardening. carrier gas The gas used to carry the carbylamine reaction /kar-băl-ă-meen, sample in gas chromatography. -am-in/ See isocyanide test. case hardening Processes for increasing carcinogen /kar-sin-ŏ-jĕn/ An agent that the hardness of the surface or ‘case’ of the causes cancer in animals, such as tobacco steel used to make such components as smoke or ionizing radiation. gears and crankshafts. The oldest method is carburizing, in which the carbon content Carius method /kah-ree-ŭs/ A method of the surface layer is increased by heating in quantitative analysis for identifying in a carbon-rich environment. Nitriding in- halogens, phosphorus, and sulfur in or- volves the diffusion of nitrogen into the ganic compounds. The compound is surface layer of steel forming intensely heated with concentrated nitric acid, which hard nitride particles in the structure. A oxidizes the organic matter and leaves the combination of both carburizing and ni- element in a form in which it can be de- triding is sometimes employed. tected by normal qualitative analysis. The method is named for the German chemist casein /kay-seen, -see-in/ A phosphorus- Georg Ludwig Carius (1829–75). containing protein that occurs in milk and cheese. It is easily digested by young mam- carnallite /kar-nă-lÿt/ A mineral chlo- mals and is their major source of protein ride of potassium and magnesium, and phosphorus. It has been used in the KCl.MgCl2.6H2O. manufacture of paper and buttons.

Carnot cycle /kar-noh/ The idealized re- cast iron Alloys of iron and carbon versible cycle of four operations occurring made by remelting the crude iron produced in a perfect heat engine. These are the suc- in a blast furnace. The carbon content is cessive adiabatic compression, isothermal usually between 2.4 and 4.0% and may be expansion, adiabatic expansion, and present as iron carbide (white cast iron) or isothermal compression of the working as graphite (gray cast iron). Metals can be substance. The cycle returns to its initial added to improve the properties of the

55 catabolism alloy. Additional elements such as phos- catalytic converter /kat-ă-lit-ik/A de- phorus, sulfur, and manganese are also vice fitted to the exhaust system of gaso- present as impurities. Cast iron is a cheap line-fuelled vehicles to remove pollutant metal with an extensive range of possible gases from the exhaust. It consists of a hon- properties and it has been used on a very eycomb structure (to provide maximum large scale. area) coated with platinum, palladium, and rhodium catalysts. Such devices can catabolism /kă-tab-ŏ-liz-ăm/ All the convert carbon monoxide to carbon diox- metabolic reactions that break down com- ide, oxides of nitrogen to nitrogen, and un- plex molecules to simpler compounds. The burned fuel to carbon dioxide and water. function of catabolic reactions is to provide energy. See also metabolism. catalytic cracking The conversion, using a catalyst, of long-chain hydrocarbons from the refining of petroleum into catalyst /kat-ă-list/ A substance that al- more useful shorter-chain compounds such ters the rate of a chemical reaction without as those occurring in kerosene and gaso- itself being changed chemically in the reac- line. tion. The catalyst can, however, undergo physical change; for example, large lumps catechol /kat-ĕ-chohl, -kohl/ (1,2-dihy- of catalyst can, without loss in mass, be droxybenzene) A colourless crystalline converted into a powder. Small amounts of PHENOL containing two hydroxyl groups. It catalyst are often sufficient to increase the is used in photographic developing. rate of reaction considerably. A positive catalyst increases the rate of a reaction and catecholamine /kat-ĕ-chohl-ă-meen, -kohl-/ a negative catalyst reduces it. Homoge- Any of a group of important amines that neous catalysts are those that act in the contain a catechol ring in their molecules. same phase as the reactants (i.e. in gaseous They are neurotransmitters and hormones. and liquid systems). For example, nitro- Examples are epinephrine and norepineph- gen(II) oxide gas will catalyze the reaction rine. between sulfur(IV) oxide and oxygen in the gaseous phase. Heterogeneous catalysts act catenation /kat-ĕ-nay-shŏn/ The forma- in a different phase from the reactants. For tion of chains of atoms in molecules. example, finely divided nickel (a solid) will catalyze the hydrogenation of oil (liquid). cathode /kath-ohd/ In electrolysis, the The function of a catalyst is to provide electrode that is at a negative potential a new pathway for which the rate-deter- with respect to the anode. In any electrical mining step has a lower activation energy system, such as a discharge tube or elec- than in the uncatalyzed reaction. A catalyst tronic device, the cathode is the terminal at which electrons enter the system. does not change the products in an equilibrium reaction and their concentration is cation /kat-ÿ-ŏn, -on/ A positively identical to that in the uncatalyzed reac- charged ion, formed by removal of elec- tion; i.e. the position of the equilibrium re- trons from atoms or molecules. In electrol- mains unchanged. The catalyst simply ysis, cations are attracted to the negatively increases the rate at which equilibrium is charged electrode (the cathode). Compare attained. anion. In autocatalysis, one of the products of the reaction itself acts as a catalyst. In this cationic detergent /kat-ÿ-on-ik/ See de- type of reaction the reaction rate increases tergent. with time to a maximum and finally slows down. For example, in the hydrolysis of cationic resin An ION-EXCHANGE mater- ethyl ethanoate, the ethanoic acid pro- ial that can exchange cations, such as H+ duced catalyzes the reaction. and Na+, for ions in the surrounding

56 centigrade scale medium. Such resins are used for a wide e.m.f. of the cell is stated as +1.10 volts. See range of purification and analytical pur- also accumulator; Leclanché cell. poses. They are often produced by adding a cellulose /sel-yŭ-lohs/ A polysaccharide – + sulfonic acid group (–SO3 H ) or a car- (C6H10O5)n of glucose, which is the main boxylate group (–COO–H+) to a stable constituent of the cell walls of plants. It is polyphenylethene resin. A typical exchange obtained from wood pulp. reaction is: – + – + resin–SO3 H + NaCl = resin–SO3 Na cellulose acetate (cellulose ethanoate) + HCl A polymeric substance made by acetylating They have been used to great effect to sep- cellulose. It is used in plastics, in acetate arate mixtures of cations of similar size film, and in acetate rayon. having the same charge. Such mixtures can be attached to cationic resins and progres- cellulose trinitrate /trÿ-nÿ-trayt/ (gun sive elution will recover them in order of cotton; nitrocellulose) A highly flamma- decreasing ionic radius. Promethium was ble substance made by treating cellulose first isolated using this technique. with a nitric–sulfuric acid mixture. Cellu- lose trinitrate is used in explosives and in caustic lime See calcium hydroxide. lacquers. It is an ester of nitric acid (i.e. not a true nitro compound). caustic potash See potassium hydroxide. Celsius scale A TEMPERATURE SCALE in which the temperature of melting pure ice See sodium hydroxide. caustic soda is taken as 0° and the temperature of boiling water 100° (both at standard pressure). celestine /sel-ĕ-stÿn, -stin/ A mineral sul- The degree Celsius (°C) is equal to the fate of strontium, SrSO . 4 kelvin. This was known as the centigrade scale until 1948, when the present name cell A system having two plates (elec- became official. Celsius’ original scale was trodes) in a conducting liquid (electrolyte). inverted (i.e. had 0° as the steam tempera- An electrolytic cell is used for producing a ° chemical reaction by passing a current ture and 100 as the ice temperature). The scale is named for the Swedish astronomer through the electrolyte (i.e. by ELECTROLY- Anders Celsius (1701–44). SIS). A voltaic (or galvanic) cell produces an e.m.f. by chemical reactions at each electrode. Electrons are transferred to or from cement A powdered mixture of calcium the electrodes, giving each a net charge. silicates and aluminates, which is made by There is a convention for writing cell re- heating limestone (CaCO3) with clay, and actions in voltaic cells. The DANIELL CELL, grinding the result. When mixed with for instance, consists of a zinc electrode in water, reactions occur with the water a solution of Zn2+ ions connected (through (hence the name hydraulic cement) and a a porous pot) to a solution of Cu2+ ions in hard solid aluminosilicate is formed. which is placed a copper electrode. The reactions at the electrodes are cementite /sĕ-men-tÿt/ (Fe3C) A con- Zn → Zn2+ + 2e stituent of certain cast irons and steels. The i.e. oxidation of the zinc to zinc(II), and presence of cementite increases the hard- Cu2+ + 2e → Cu ness of the metal. i.e. reduction of copper(II) to copper. A cell reaction of this type is written: centi- Symbol: c A prefix denoting 10–2. Zn|Zn2+(aq)|Cu2+(aq)|Cu For example, 1 centimeter (cm) = 10–2 The e.m.f. is the potential of a lead on the meter (m). right minus the potential of a lead on the left. Copper is positive in this case and the centigrade scale See Celsius scale.

57 centrifugal pump centrifugal pump A device commonly crystals and is often found together with used for transporting fluids around a galena (PbS). chemical plant. Centrifugal pumps usually have 6–12 blades rotating inside a fixed cesium /see-zee-ŭm, see-see-/ (caesium) circular casing. As the blades rotate, the A soft golden highly reactive low-melting fluid is impelled out of the pump along a element of the alkali-metal group. It is pipe. Centrifugal pumps do not produce found in several silicate minerals, including high pressures but they have the advantage pollucite (CsAlSi2O6). The metal oxidizes of being relatively cheap because they are in air and reacts violently with water. Ce- simple in design, have no valves, and work sium is used in photocells, as a catalyst, at high speeds. In addition they are not and in the cesium atomic clock. The ra- 134 damaged if a blockage develops. Compare dioactive isotopes Cs (half life 2.065 137 displacement pump. years) and Cs (half life 30.3 years) are produced in nuclear reactors and are po- centrifuge /sen-tră-fyooj/ An apparatus tentially dangerous atmospheric pollu- for rotating a container at high speeds, tants. ° ° used to increase the rate of sedimentation Symbol: Cs; m.p. 28.4 C; b.p. 678.4 C; ° of suspensions or the separation of two im- r.d. 1.873 (20 C); p.n. 55; r.a.m. 132.91. miscible liquids. See also ultracentrifuge. cesium-chloride structure A form of ceramics /sĕ-ram-iks/ Useful high-melt- crystal structure that consists of alternate ing inorganic materials. Ceramics include layers of cesium ions and chloride ions with the center of the lattice occupied by a silicates and aluminosilicates, refractory cesium ion in contact with eight chloride metal oxides, and metal nitrides, borides, ions (i.e. four chloride ions in the plane etc. Pottery and porcelain are examples of above and four in the plane below). ceramics. CFC Chlorofluorocarbon. See halocar- cerium /seer-ee-ŭm/ A ductile malleable bon. gray element of the lanthanoid series of metals. It occurs in association with other c.g.s. system A system of units that uses lanthanoids in many minerals, including the centimeter, the gram, and the second as monazite and bastnasite. The metal is reac- the base mechanical units. Much early sci- tive; it reacts with water and tarnishes in entific work used this system, but it has air. It is used in several alloys (especially now almost been abandoned. for lighter flints), as a catalyst, and in compound form in carbon-arc searchlights, chain When two or more atoms form etc., and in the glass industry. bonds with each other in a molecule, a ° ° Symbol: Ce; m.p. 799 C; b.p. 3426 C; chain of atoms results. This chain may be a ° r.d. 6.7 (hexagonal structure, 25 C); p.n. straight chain, in which each atom is added 58; r.a.m. 140.15. to the end of the chain, or it may be a branched chain, in which the main chain of cermet /ser-met/ A synthetic composite atoms has one or more smaller SIDE CHAINS material made by combining a ceramic and branching off it. a sintered metal. Cermets have better temperature and corrosion resistance than chain reaction A self-sustaining chemi- straight ceramics. For example, a cal reaction consisting of a series of steps, chromium–alumina cermet is used to make each of which is initiated by the one before blades for gas-turbine engines. it. An example is the reaction between hydrogen and chlorine: → cerussite /seer-ŭ-sÿt/ A naturally occur- Cl2 2Cl• → ring form of lead(II) carbonate that is an H2 + Cl• HCl + H• → important lead ore. It forms orthorhombic H• + Cl2 HCl + Cl• 58 chemical bond

→ α θ 2H• H2 V = V0(1 + v ) → θ° 2Cl• Cl2 where V is the volume at temperature C ° α The first stage, chain initiation, is the dis- and V0 the volume at 0 C. The constant v sociation of chlorine molecules into atoms; is the thermal expansivity of the gas. For an this is followed by two chain propagation ideal gas its value is 1/273.15. reactions. Two molecules of hydrogen A similar relationship exists for the chloride are produced and the ejected chlo- pressure of a gas heated at constant vol- rine atom is ready to react with more hy- ume: α θ drogen. The final steps, chain termination, p = p0(1 + p ) α stop the reaction. Here, p is the pressure coefficient. For an Induced nuclear fission reactions de- ideal gas α α pend on chain reactions; the fission reac- p = v tion is maintained by the two or three although they differ slightly for real gases. neutrons set free in each fission. It follows from Charles’ law that for a gas heated at constant pressure, chair conformation See conformation. V/T = K where T is the thermodynamic temperature chalcogens /chal-kŏ-jĕnz/ See group 16 and K is a constant. Similarly, at constant elements. volume, p/T is a constant. Charles’ volume law is sometimes chalk A natural form of calcium carbon- called Gay-Lussac’s law after its indepen- ate (CaCO3) formed originally by marine dent discoverer. The law is named for both organisms. (Blackboard chalk is calcium the French physicist and physical chemist sulfate, CaSO4.) Jacques Alexandre César Charles (1746–1823) and for the French physicist chamber process See lead-chamber Joseph-Louis Gay-Lussac (1778–1850). process. See also absolute temperature; gas laws. chaotic reaction A chemical reaction in chelate /kee-layt/ A metal coordination which the concentrations of the reactants complex in which one ligand coordinates show chaotic behavior, i.e. the evolution of at two or more points to the same metal the reaction may become unpredictable. ion. The resulting complex contains rings Reactions of this type ususally involve a of atoms that include the metal atom. An large number of complex interlinked example of a chelating agent is 1,2-di- steps. aminoethane (H2NCH2CH2NH2), which can coordinate both its amine groups to the charcoal An amorphous form of carbon same atom. It is an example of a bidentate made by heating wood or other organic ligand (having two ‘teeth’). Edta, which material in the absence of air. Activated can form up to six bonds, is another exam- charcoal is charcoal that has been heated to ple of a chelating agent. The word chelate drive off absorbed gas. It is used for ab- comes from the Greek word meaning sorbing gases and for removing impurities ‘claw’. See also sequestration. from liquids. chemical bond A link between atoms Charles’ law /sharlz, charl-ziz/ For a that leads to an aggregate of sufficient sta- given mass of gas at constant pressure, the bility to be regarded as an independent volume increases by a constant fraction of molecular species. Chemical bonds include the volume at 0°C for each Celsius degree covalent bonds, electrovalent (ionic) rise in temperature. The constant fraction bonds, coordinate bonds, and metallic (α) has almost the same value for all gases bonds. Hydrogen bonds and van der Waals – about 1/273 – and Charles’ law can be forces are not usually regarded as true written in the form chemical bonds.

59 chemical combination, laws of chemical combination, laws of A chemical equation A method of repre- group of chemical laws developed during senting a chemical reaction using chemical the late 18th and early 19th centuries, formulas (see formula). The formulas of which arose from the recognition of the im- the reactants are given on the left-hand side portance of quantitative (as opposed to of the equation, with the formulas of the qualitative) study of chemical reactions. products on the right. The two halves are The laws are: separated by a directional arrow or arrows 1. the law of conservation of mass (mat- (on an equals sign). A number preceding a ter); formula (called a stoichiometric coeffi- 2.the law of constant (definite) propor- cient) indicates the number of molecules of tions; that substance involved. The equation 3. the law of multiple proportions; must balance – that is, the number of 4. the law of equivalent (or reciprocal) pro- atoms of any one element must be the same portions, on both sides of the equation. A simple ex- These laws played a significant part in Dal- ample is the equation for the reaction be- ton’s development of his atomic theory tween hydrogen and oxygen to form water: → (1808). See conservation of mass, law of; 2H2 + O2 2H2O constant proportions, law of; equivalent A more complex equation represents the proportions, law of; multiple proportions, reaction between disodium tetraborate law of. (borax) and aqueous hydrochloric acid to give boric acid and sodium chloride: → chemical dating A method of using Na2B4O7 + 2HCl + 5H2O 4H3BO3 + chemical analysis to find the age of an ar- 2NaCl chaeological specimen in which composi- tional changes have taken place over time. chemical equilibrium See equilibrium. For example, the determination of the amount of fluorine in bone that has been chemical formula See formula. buried gives an indication of its age because phosphate in the bone has gradually chemical potential Symbol: µ. For the been replaced by fluoride ions from ith component of a mixture the chemical µ groundwater. Another dating technique potential i is defined by the partial deriva- depends on the fact that, in living organ- tive of the Gibbs free energy G of the sys- isms, amino acids are optically active. tem with respect to the amount ni of the After death a slow racemization reaction component, when the temperature, pres- occurs and a mixture of L- and D-isomers sure, and amounts of other components µ ∂ ∂ forms. The age of bones can be accurately are constant, i.e. i = G/ ni. If the chemi- determined by measuring the relative cal potentials of components are equal amounts of L- and D-amino acids present. then the components are in equilibrium. Also, in a one-component system with two chemical engineering The branch of phases it is necessary for the chemical po- engineering concerned with the design and tentials to be equal in the two phases for maintenance of a chemical plant and its there to be equilibrium. ability to withstand extremes of temperature and pressure, corrosion, and wear. It chemical reaction A process in which enables laboratory processes producing one or more elements or chemical com- grams of material to be converted into a pounds (the reactants) react to produce a large-scale plant producing tonnes of mate- different substance or substances (the rial. Chemical engineers plan large-scale products). chemical processes by linking together the appropriate unit processes and by studying chemical shift An effect of chemical such parameters as heat and mass transfer, structure on the position of a spectral line. separations, and distillations. See nuclear magnetic resonance.

60 chloric acid chemical symbol A letter or pair of let- chloral hydrate See trichloroethanal. ters that stand for a chemical element, as used in chemical formulas and equations. chloramine /klor-ă-meen, kloh-ră-/ See chemical equation; formula. (NH2Cl) A colorless liquid made by reacting ammonia with sodium chlorate(I) chemiluminescence /kem-ă-loo-mă-nes- (NaOCl). It is formed as an intermediate in ĕns/ The emission of light during a chem- the production of hydrazine. Chloramine is ical reaction. unstable and changes explosively into ammonium chloride and nitrogen trichloride. chemisorption /kem-ă-sorp-shŏn, -zorp-/ See adsorption. chlorate /klor-ayt, kloh-rayt/ A salt of chloric(V) acid. Chile saltpeter /chil-ee/ See sodium nitrate. chloric(I) acid (hypochlorous acid; HClO) A colorless liquid produced when china clay (kaolin) A white powder ob- chlorine is dissolved in water. It is a bleach tained from the natural decomposition of and gives chlorine water its disinfectant granites. It is used as a filler in paper-mak- properties. To increase the yield of acid, ing, in the pottery industries, and in phar- the chlorine water can be shaken with a maceuticals. See kaolinite. small amount of mercury(II) chloride. The Cl–O bond is broken more easily than the chiral /kÿr-ăl/ Having the property of O–H bond in aqueous solution; the acid is chirality. For example, lactic acid is a chi- consequently a poor proton donor and ral compound because it has two possible hence a weak acid. structures that cannot be superposed. See optical activity. chloric(III) acid (chlorous acid; HClO2) A pale yellow liquid produced by reacting chirality /kÿr-al-ă-tee/ The property of chlorine dioxide with water. It is a weak existing in left- and right-handed forms; acid and oxidizing agent. i.e. forms that are not superposable in three-dimensional space. In chemistry the chloric(V) acid (chloric acid; HClO3)A term is applied to the existence of optical colorless liquid with a pungent odor, isomers. See optical activity. formed by the action of dilute sulfuric acid on barium chlorate. It is a strong acid and chirality element A part of a molecule has bleaching properties. Chloric(V) acid is that causes it to display chirality. The most a strong oxidizing agent and in concen- common type of element is a chirality centrated solution it will ignite organic sub- ter, which is an atom attached to four dif- stances, such as paper and sugar. ferent atoms or groups. This is also referred to as an asymmetric atom. Less chloric(VII) acid (perchloric acid; commonly a molecule may have a chirality HClO4) A colorless liquid that fumes axis, as in the case of certain substituted al- strongly in moist air. It is made by vacuum lenes of the type R1R2C=C=CR3R4. In this distillation of a mixture of potassium per- form of compound the R1 and R2 groups chlorate and concentrated sulfuric acid. In do not lie in the same plane as the R3 and contact with organic material it is danger- R4 groups because of the nature of the dou- ously explosive. ble bonds. The chirality axis lies along the The hydrate (HClO4.H2O) of chlo- C=C=C chain. It is also possible to have ric(VII) acid is a white crystalline solid at molecules that contain a chirality plane. room temperature and has an ionic lattice + – See optical activity. structure of the form (H3O) (ClO4) . chloral /klor-ăl, kloh-răl/ See trichloro- chloric acid /klor-ik, kloh-rik/ See chlo- ethanal. ric(V) acid.

61 chloride

→ chloride /klor-ÿd, kloh-rÿd/ See halide; ZnCl2 + H2O Zn(OH)Cl + HCl → chlorine. FeCl3 + 3H2O Fe(OH)3 + 3HCl Chlorine forms four oxides, chlorine chlorination /klor-ă-nay-shŏn, kloh-ră-/ monoxide, Cl2O; chlorine dioxide, ClO2; 1. Treatment with chlorine; for instance, chlorine hexoxide, Cl2O6; and chlorine the use of chlorine to disinfect water. heptoxide, Cl2O7; all of which are highly 2. See halogenation. reactive and explosive. Chlorine dioxide finds commercial application as an active chlorine /klor-een, -in, kloh-reen, -rin/A oxidizing agent but because of its explosive green reactive gaseous element belonging nature it is usually diluted by air or other to the halogens; i.e. group 17 (formerly gases. The chloride ion is able to function VIIA) of the periodic table. It occurs in sea- as a ligand with a large variety of metal – water, salt lakes, and underground de- ions forming such species as [FeCl4] , 3– + posits of halite, NaCl. It accounts for about [CuCl4] , and [Co(NH3)4Cl2] . The for- 0.055% of the Earth’s crust. Chlorine is mation of anionic chloro-complexes is ap- strongly oxidizing and can be liberated plied to the separation of metals by from its salts only by strong oxidizing anion-exchange methods. agents, such as manganese(IV) oxide, Because of the hydrolysis of many metal potassium permanganate(VII), or potas- chlorides when solutions are evaporated, sium dichromate; note that sulfuric acid is special techniques must be used to prepare not sufficiently oxidizing to release chlo- anhydrous chlorides. These are: rine from chlorides. Industrially, chlorine 1. reaction of dry chlorine with the hot is prepared by the electrolysis of brine and metal; in some processes chlorine is recovered by 2. reaction of dry hydrogen chloride with the hot metal (lower valences); the high-temperature oxidation of waste 3. reaction of dry hydrogen chloride on the hydrochloric acid. Chlorine is used in large hydrated chloride. quantities, both as the element, to produce The solubility of inorganic metal chlorides chlorinated organic solvents, and for the is such that they are not an environmental production of polyvinyl chloride (PVC), problem unless the metal ion itself is toxic the major thermoplastic in use today, and but many organochlorine compounds are in the form of hypochlorites for bleaching. sufficiently stable for the accumulated Chlorine reacts directly and often vig- residues of chlorine-containing pesticides orously with many elements; it reacts ex- to present a severe problem in some areas. plosively with hydrogen in sunlight to form This arises because they can accumulate in hydrogen chloride, HCl, and combines food chains and concentrate in the tissues with the electropositive elements to form of higher animals (see DDT). Chlorine and metal chlorides. The metals of main groups hydrogen chloride are both highly toxic. 1 and 2 form ionic chlorides but an in- Thus chlorides that hydrolyze to release crease in the metal charge/size ratio leads HCl should also be regarded as toxic. As to the chlorides becoming increasingly co- organochlorine compounds are frequently valent. For example, CsCl is totally ionic, even more toxic, they should not be han- AlCl3 has a layer lattice, and TiCl4 is es- dled without gloves and precautions sentially covalent. The electronegative ele- should be taken against inhalation. ments form volatile molecular chlorides Symbol: Cl; m.p. –100.38°C; b.p. characterized by the single covalent bond –33.97°C; d. 3.214 kg m–3 (0°C); p.n. 17; to chlorine. With the exception of Pb2+, r.a.m. 35.4527. + 2+ Ag , and Hg2 , the ionic chlorides are soluble in water, dissolving to give the hy- chlorine dioxide /dÿ-oks-ÿd, -id/ – drated metal ion and the chloride ion Cl . (ClO2) An orange gas formed by the ac- Chlorides of metals other than the most tion of concentrated sulfuric acid on potas- electropositive are hydrolyzed if aqueous sium chlorate. It is a powerful oxidizing solutions are evaporated; for example, agent and its explosive properties in the

62 chloroplatinic acid presence of a reducing agent were used to ethanoic acid with chlorine, using red make one of the first matches. It is widely phosphorus. It is a stronger acid than used in the purification of water and as a ethanoic acid because of the electron-with- bleach in the flour and wood-pulp indus- drawing effect of the chlorine atom. try. On an industrial scale an aqueous so- Dichloroethanoic acid (dichloroacetic lution of chlorine dioxide is made by acid, CHCl2COOH) and trichloroethanoic passing nitrogen dioxide up a tower acid (trichloroacetic acid, CCl3COOH) are packed with a fused mixture of aluminum made in the same way. The acid strength oxide and clay, down which a solution of increases with the number of chlorine sodium chlorate flows. atoms present. chlorine monoxide /mon-oks-ÿd, -id/ chloroethene /klor-oh-eth-een, kloh-roh-/ See dichlorine oxide. (vinyl chloride; H2C:CHCl) A gaseous organic compound used in the manufac- chlorine(I) oxide See dichlorine oxide. ture of PVC (polyvinyl chloride). Chloro- ethene is manufactured by the reaction chlorite /klor-ÿt, kloh-rÿt/ A chlorate(III) between ethyne and hydrogen chloride salt; i.e. a salt of chloric(III) acid (chlorous using a mercury(II) chloride catalyst: acid). → C2H2 + HCl H2C:CHCl An alternative source, making use of the klor-oh-ă-see-tik, -set- chloroacetic acid / ready supply of ethene, is via dichloro- ik, kloh-roh-/ See chloroethanoic acid. ethane: H C:CH + Cl → CH Cl.CH Cl → chlorobenzene /klor-oh-ben-zeen, klor- 2 2 2 2 2 H C:CHCl oh-ben-zeen, kloh-roh-/ (monochloroben- 2 zene; C H Cl) A colorless liquid made by 6 5 chlorofluorocarbon /klor-ŏ-floo-ŏ-rŏ- the catalytic reaction of chlorine with ben- kar-bŏn, kloh-roh-/ See halocarbon. zene. It can be converted to phenol by reaction with sodium hydroxide under /klor-ŏ-form, kloh-rŏ-/ See extreme conditions (300°C and 200 atmos- chloroform pheres pressure). It is also used in the man- trichloromethane. ufacture of other organic compounds. chloromethane /klor-ŏ-meth-ayn, kloh- 2-chlorobuta-1,3-diene /klor-ŏ-byoo-tă- roh-/ (methyl chloride; CH3Cl) dÿ-een, kloh-roh- / (chloroprene; H C:CH. 2 chlorophylls /klor-ŏ-filz, kloh-rŏ-/ The CCl:CH2) A colorless liquid derivative of butadiene used in the manufacture of neo- pigments present in plants that act as cata- prene rubber. lysts in the photosynthesis of carbohydrates from carbon dioxide and water. chlorobutyl /klor-oh-byoo-t’l, kloh-roh-/ There are four types, known as chloro- See butyl rubber. phylls a, b, c, and d. chloroethane /klor-oh-eth-ayn, kloh-roh-/ chloroplatinic acid /klor-ŏ-plă-tin-ik, kloh-rŏ-/ (platinic chloride; H PtCl )A (ethyl chloride; C2H5Cl) A gaseous com- 2 6 pound made by the addition of hydrogen reddish compound prepared by dissolving chloride to ethene. It is used as a refriger- platinum in aqua regia. When crystallized ant and a local anesthetic. from the resulting solution, crystals of the hexahydrate (H2PtCl6.6H2O) are ob- chloroethanoic acid /klor-oh-eth-ă-noh- tained. The crystals are needle-shaped and ik, kloh-roh-/ (chloroacetic acid; deliquesce on exposure to moist air. CH2ClCOOH) A colorless crystalline Chloroplatinic acid is a relatively strong solid made by substituting one of the hy- acid, giving rise to the family of chloro- drogen atoms of the methyl group of platinates.

63 chloroprene chloroprene /klor-ŏ-preen, kloh-rŏ-/ See phy. In the other main type of chromato- 2-chlorobuta-1,3-diene. graphy, planar chromatography, the stationary phase is a flat sheet of absorbent chlorous acid /klor-ŭs, kloh-rŭs/ See material. See paper chromatography; thin- chloric(III) acid. layer chromatography. Components of the mixture are held cholesteric crystal /kŏ-less-tĕ-rin/ See back by the stationary phase either by ad- liquid crystal. sorption (e.g. on the surface of alumina) or because they dissolve in it (e.g. in the mois- chromate /kroh-mayt/ Any oxygen-con- ture within chromatography paper). taining derivative of chromium. Usually the term is reserved for the chromate(VI) chrome alum /krohm/ See alum. species. chromic anhydride /kroh-mik/ See chromatography /kroh-mă-tog-ră-fee/ chromium(VI) oxide. A technique used to separate or analyze complex mixtures. A number of related chromic oxide See chromium(III) techniques exist; all depend on two phases: oxide. a mobile phase, which may be a liquid or a gas, and a stationary phase, which is either chromite /kroh-mÿt/ (chrome iron ore; a solid or a liquid held by a solid. The sam- FeCr2O4) A mineral that consists of ple to be separated or analyzed is carried mixed oxides of chromium and iron, the by the mobile phase through the stationary principal ore of chromium. It occurs as phase. Different components of the mix- black masses with a metallic luster. ture are absorbed or dissolved to different extents by the stationary phase, and conse- chromium /kroh-mee-ŭm/ A transition quently move along at different rates. In metal that occurs naturally as chromite this way the components are separated. (FeO.Cr O ), large deposits of which are There are many different forms of chro- 2 3 found in Zimbabwe. The ore is converted matography depending on the phases used into sodium dichromate(VI) and then re- and the nature of the partition process be- duced with carbon to chromium(III) oxide tween mobile and stationary phases. The and finally to metallic chromium with alu- main classification is into column chromatography and planar chromatography. minum. Chromium is used in strong alloy A simple example of column chro- steels and stainless steel and for plating ar- matography is in the separation of liquid ticles. It is a hard silvery metal that resists mixtures. A vertical column is packed with corrosion at normal temperatures. It reacts an absorbent material, such as alumina slowly with dilute hydrochloric and sulfu- (aluminum oxide) or silica gel. The sample ric acids to give hydrogen and blue is introduced into the top of the column chromium(II) compounds, which quickly and washed down it using a solvent. This oxidize in air to green chromium(III) ions. process is known as elution; the solvent The oxidation states are +6 in chromates 2– 2– used is the eluent and the sample being sep- (CrO4 ) and dichromates (Cr2O7 ), +3 arated is the eluate. If the components are (the most stable), and +2. In acidic solu- colored, visible bands appear down the tions the yellow chromate(VI) ion changes column as the sample separates out. The to the orange dichromate(VI) ion. Dichro- components are separated as they emerge mates are used as oxidizing agents in the from the bottom of the column. In this par- laboratory; for example as a test for sul- ticular example of chromatography the fur(IV) oxide (sulfur dioxide) and to oxi- partition process is adsorption on the par- dize alcohols. ticles of alumina or silica gel. Column Symbol: Cr; m.p. 1860±20°C; b.p. chromatography can also be applied to 2672°C; r.d. 7.19 (20°C); p.n. 24; r.a.m. mixtures of gases. See gas chromatogra- 51.9961.

64 citric acid chromium(II) oxide (chromous oxide; of potassium dichromate and sodium chlo- CrO) A black powder prepared by the ride with concentrated sulfuric acid or by oxidation of chromium amalgam with di- the action of concentrated sulfuric acid on lute nitric acid. At high temperatures chromium(VI) oxide dissolved in concen- (around 1000°C) chromium(II) oxide is re- trated hydrochloric acid. Chromyl chloride duced by hydrogen. is hydrolyzed by water, and with solutions of alkalis it undergoes immediate hydroly- chromium(III) oxide (chromic oxide; sis to produce chromate ions. It is used as chromium sesquioxide; Cr2O3) A green an oxidizing agent in organic chemistry. powder that is almost insoluble in water. It Chromyl chloride oxidizes methyl groups is isomorphous with iron(III) oxide and at the ends of aromatic side chains to alde- aluminum(III) oxide. Chromium(III) oxide hyde groupings (Étard’s reaction). is prepared by gently heating chromium(III) hydroxide or by heating cinnabar /sin-ă-bar/ See mercury(II) sul- ammonium dichromate. Alternative prepa- fide. rations include the heating of a mixture of ammonium chloride and potassium cinnamic acid /să-nam-ik, sin-ă- dichromate or the decomposition of mik/ See 3-phenylpropenoic acid. chromyl chloride by passing it through a red-hot tube. Chromium(III) oxide is used CIP system (Cahn–Ingold–Prelog system) as a pigment in the paint and glass indus- A method of producing a sequence rule tries. used in the absolute description of stereoisomers in the R–S convention (see chromium(IV) oxide (chromium diox- optical activity) or the E-Z CONVENTION. ide; CrO2) A black solid prepared by The rule is to consider the atoms that are heating chromium(III) hydroxide in oxy- bound directly to a chiral center (or to a gen at a temperature of 300–350°C. double bond). The group in which this Chromium(IV) oxide is very unstable. atom has the highest proton number has the highest priority. So, for example, in > chromium(VI) oxide (chromium triox- HCClBr(NH2), the order of priority is Br > > ide; chromic anhydride; CrO3) A red Cl NH2 H. If two atoms are the same, crystalline solid formed when concentrated the substituents are considered, with the sulfuric acid is added to a cold saturated substituents of highest proton number tak- solution of potassium dichromate. The ing precedence. So in long prismatic needle-shaped crystals that C(NH2)(NO2)(CH3)(C2H6 ) > > > are produced are extremely deliquescent. the order is NO2 NH2 C2H6 CH3. Chromium(VI) oxide is readily soluble in The system is named after the British water, forming a solution that contains chemists Robert Cahn (1899–1981) and several of the polychromic acids. On heat- Sir Christopher Ingold (1893–1970) and ing it decomposes to give chromium(III) the Bosnian–Swiss chemist Vladimir Prelog oxide. Chromium(VI) oxide is used as an (1906– ). oxidizing reagent. cis- Designating an isomer with groups chromophore /kroh-mŏ-for, -fohr/A that are adjacent. See isomerism. group of atoms in a molecule that is responsible for the color of the compound. cis-trans isomerism /sis-tranz/ See isomerism. chromous oxide /kroh-mŭs/ See chromium(II) oxide. citric acid /sit-rik/ A white crystalline carboxylic acid important in plant and an- chromyl chloride /kroh-măl/ imal cells. It is present in many fruits. The (CrO2Cl2) A dark red covalent liquid systematic name is 2-hydroxypropane- prepared either by distilling a dry mixture 1,2,3-tricarboxylic acid. The formula is:

65 Claisen condensation

HOOCCH2C(OH)(COOH)CH2COOH tice are large enough to permit entrance or emergence of the guest without breaking Claisen condensation /klÿ-zĕn/ A reac- bonds in the host lattice. Quinol forms tion in which two molecules of ester com- many clathrates, e.g. with SO2; water (ice) bine to give a keto-ester – a compound forms a clathrate with xenon. containing a ketone group and an ester group. The reaction is base-catalyzed by clays Naturally occurring aluminosili- sodium ethoxide; the reaction of ethyl cates which form pastes and gels with ethanoate refluxed with sodium ethoxide water. gives: → 2CH3.CO.OC2H5 cleavage The splitting of a crystal along CH3.CO.CH2.CO.OC2H5 + C2H5OH planes of atoms, to form smooth surfaces. The mechanism is similar to that of the aldol reaction, the first step being forma- close packing The arrangement of par- tion of a carbanion from the ester: ticles (usually atoms) in crystalline solids in – → CH3COC2H5 + OC2H5 which each particle has 12 nearest neigh- – CH2COC2H5 + C2H5OH bors: six in the same layer (or plane) as it- This attacks the carbon atom of the car- self and three each in the layer above and bonyl group on the other ester molecule, below. This arrangement provides the forming an intermediate anion that decom- most economical use of space. The two poses to the keto-ester and the ethanoate principal types are cubic close packing and ion. The reaction is named for the German hexagonal close packing. organic chemist Ludwig Claisen (1851– 1930). cluster compound A type of compound in which a cluster of metal atoms are joined Clark cell A type of cell formerly used by metal–metal bonds. Cluster compounds as a standard source of e.m.f. It consists of are formed by certain transition elements, a mercury cathode coated with mercury such as molybdenum and tungsten. sulfate, and a zinc anode. The electrolyte is zinc sulfate solution. The e.m.f. produced coagulation /koh-ag-yŭ-lay-shŏn/ The is 1.4345 volts at 15°C. The Clark cell has association of particles (e.g. in colloids) been superseded as a standard by the We- into clusters. See flocculation. ston (Trademark) cadmium cell. The cell is named for the English engineer Josiah La- coal A black mineral that consists timer Clark (1822–98). mainly of carbon, used as a fuel and as a source of organic chemicals. It is the fos- clathrate /klath-rayt/ (enclosure com- silized remains of plants that grew in the pound) A substance in which small Carboniferous and Permian periods and (guest) molecules are trapped within the were buried and subjected to high pres- lattice of a crystalline (host) compound. sures underground. There are various types Clathrates are formed when suitable host of coal, classified according to their in- compounds are crystallized in the presence creasing carbon content. See anthracite; bi- of molecules of the appropriate size. Al- tuminous coal; lignite. though the term ‘clathrate compound’ is often used, they are not true compounds; coal gas A fuel gas made by heating coal no chemical bonds are formed, and the in a limited supply of air. It consists mainly guest molecules interact by weak van der of hydrogen and methane, with some car- Waals forces. The clathrate is maintained bon monoxide (which makes the gas highly by the cagelike lattice of the host. The host poisonous). COAL TAR and coke are formed lattice must be broken down, for example, as by-products. by heating or dissolution in order to release the guest. This should be compared with coal tar Tar produced by heating coal in zeolites, in which the holes in the host lat- the absence of oxygen. It is a mixture of

66 colligative properties many organic compounds (e.g. benzene, tion is never as high as when a catalyst is toluene, and naphthalene) and also con- present. A coenzyme is not a true catalyst tains free carbon. because it undergoes chemical change during the reaction. cobalt /koh-bawlt/ A lustrous silvery- blue hard ferromagnetic transition metal coherent units A system or sub-set of occurring in association with nickel. It is units (e.g. SI units) in which the derived used in alloys for magnets, cutting tools, units are obtained by multiplying or divid- and electrical heating elements and in cata- ing together base units, with no numerical lysts and some paints. factor involved. Symbol: Co; m.p. 1495°C; b.p. 2870°C; r.d. 8.9 (20°C); p.n. 27; r.a.m. coinage metals A group of malleable 58.93320. metals forming group 11 of the periodic table. (They were formerly subgroup IB.) cobaltic oxide /koh-bawl-tik/ See The metals all have an outer s1 electronic cobalt(III) oxide. configuration but they differ from the alkali metals (also outer s1) in having inner d- cobaltous oxide /koh-bawl-tŭs/ See electrons. They are copper (Cu), silver cobalt(II) oxide. (Ag), and gold (Au). The coinage metals all have much higher ionization potentials cobalt(II) oxide (cobaltous oxide; than the alkali metals and high positive CoO) A green powder prepared by the standard electrode potentials and are action of heat on cobalt(II) hydroxide in therefore much more difficult to oxidize. A the absence of air. Alternatively it may be further significant difference from the al- prepared by the thermal decomposition of kali metals is the variety of oxidation states cobalt(II) sulfate, nitrate, or carbonate, observed for the coinage metals. Thus cop- also in the absence of air. Cobalt(II) oxide per in aqueous chemistry is the familiar is a basic oxide, reacting with acids to give (hydrated) blue divalent Cu2+ ion but col- solutions of cobalt(II) salts. It is stable in orless copper(I) compounds can be pre- air up to temperatures of around 600°C, pared with groups that stabilize low after which it absorbs oxygen to form tri- valences such as CN–, e.g. CuCN. A few cobalt tetroxide. Cobalt(II) oxide can be compounds of copper(III) have also been reduced to cobalt by heating in a stream of prepared. The common form of silver is carbon monoxide or hydrogen. It is used in Ag(I), e.g. AgNO3, with a few Ag(II) com- the pottery industry and in the production pounds stable in the solid only. The most of vitreous enamels. common oxidation state of gold is Au(III), although cyanide ion again stabilizes Au(I) 3– cobalt(III) oxide (cobaltic oxide; compounds, e.g., [Au(CN)4] . The metals Co2O3) A dark gray powder formed by all form a large number of coordination the thermal decomposition of either compounds (unlike group 1) and are gen- cobalt(II) nitrate or carbonate in air. If erally treated with the other elements of the heated in air, cobalt(III) oxide undergoes appropriate transition series. further oxidation to give tricobalt tetroxide, Co3O4. coke A dense substance obtained from the carbonization of coal. It is used as a coenzymes Small organic molecules fuel and as a reducing agent. (compared to the size of an enzyme) that enable enzymes to carry out their catalytic colligative properties /kŏ-lig-ă-tiv/A activity. Examples include nicotinamide group of properties of solutions that de- adenine dinucleotide (NAD) and ubi- pends on the number of particles present, quinone (coenzyme Q). Some coenzymes rather than the nature of the particles. Col- are capable of catalyzing reactions in the ligative properties include: absence of an enzyme but the rate of reac- 1. The lowering of vapor pressure.

67 collimator

2. The elevation of boiling point. when they release flammable vapor, which 3. The lowering of freezing point. reacts with oxygen in the gas phase. Com- 4. Osmotic pressure. bustion reactions usually involve a com- Colligative properties are all based plex sequence of free-radical chain upon empirical observation. The explana- reactions. The light is produced by excited tion of these closely related phenomena de- atoms, molecules, or ions. In highly lumi- pends on intermolecular forces and the nous flames it comes from small incandes- kinetic behavior of the particles, which is cent particles of carbon. qualitatively similar to those used in deriv- Sometimes the term is also applied to ing the kinetic theory of gases. slow reactions with oxygen, and also to reactions with other gases (for example, cer- collimator /kol-ă-may-ter/ An arrange- tain metals ‘burn’ in chlorine). See also ment for producing a parallel beam of ra- spontaneous combustion. diation for use in a spectrometer or other instrument. A system of lenses and slits is common salt See sodium chloride. utilized. colloid /kol-oid/ A heterogeneous sys- complex (coordination compound)A tem in which the interfaces between type of compound in which molecules or phases, though not visibly apparent, are ions form coordinate bonds with a metal important factors in determining the sys- atom or ion. The coordinating species tem properties. The three important attrib- (called ligands) have lone pairs of elec- utes of colloids are: trons, which they can donate to the metal 1. They contain particles, commonly made atom or ion. They are molecules such as up of large numbers of molecules, form- ammonia or water, or negative ions such as ing the distinctive unit or disperse phase. Cl– or CN–. The resulting complex may be 2. The particles are distributed in a contin- neutral or it may be a complex ion. For ex- uous medium (the continuous phase). ample: 2+ → 2+ 3. There is a stabilizing agent, which has an Cu + 4NH3 [Cu(NH3)4] 3+ – → 3– affinity for both the particle and the Fe + 6CN [Fe(CN)6] 2+ – → 4– medium; in many cases the stabilizer is a Fe + 6CN [Fe(CN)6] polar group. The formation of such coordination Particles in the disperse phase typically complexes is typical of transition metals. –6 –4 have diameters in the range 10 –10 mm. Often the complexes contain unpaired Milk, rubber, and emulsion paints are typ- electrons and are paramagnetic and col- ical examples of colloids. See also sol. ored. See also chelate. See illustration over- leaf. colorimetric analysis /kul-ŏ-ră-met- rik/ Quantitative analysis in which the component /kŏm-poh-nĕnt/ One of the concentration of a colored solute is mea- separate chemical substances in a mixture sured by the intensity of the color. The test in which no chemical reactions are taking solution can be compared against standard place. For example, a mixture of ice and solutions. water has one component; a mixture of ni- columbium /kŏ-lum-bee-ŭm/ The for- trogen and oxygen has two components. mer name (in the USA) for niobium. When chemical reactions occur between the substances in a mixture, the number of column chromatography See chro- components is defined as the number of matography, gas chromatography. chemical substances present minus the number of equilibrium reactions taking ˆ combustion A reaction with oxygen place. Thus, the system: N2 + 3H2 with the production of heat and light. The 2NH3 is a two-component system. See also combustion of solids and liquids occurs phase rule.

68 condensation compound A chemical combination of concentration The amount of sub- atoms of different elements to form a substance per unit volume or mass in a solu- stance in which the ratio of combining tion. Molar concentration is amount of atoms remains fixed and is specific to that substance (in moles) per cubic decimeter substance. The constituent atoms cannot (liter). Mass concentration is mass of solute be separated by physical means; a chemical per unit volume. Molal concentration is reaction is required for the compounds to amount of substance (in moles) per kilo- be formed or to be changed. The existence gram of solute. of a compound does not necessarily imply that it is stable. Many compounds have concerted reaction A reaction that lifetimes of less than a second. See also takes place in a single stage rather than as mixture. a series of simple steps. In a concerted reaction there is a transition state in which concentrated Denoting a solution in bonds are forming and breaking at the which the amount of solute in the solvent is same time. An example is the SN2 mecha- relatively high. The term is always relative; nism in NUCLEOPHILIC SUBSTITUTION. See for example, whereas concentrated sulfuric also pericyclic reaction. acid may contain 96% H2SO4, concentrated potassium chlorate may contain as condensation /kon-den-say-shŏn/ The little as 10% KClO3. conversion of a gas or vapor into a liquid Compare dilute. or solid by cooling.

X X

X M X X M X X X square-planar

X octahedral

X X

X M X M X X X X X

tetrahedral trigonal-bipyramid Shapes of complexes

69 condensation polymerization

Nucleophile Product Name

NH3 ammonia hydroxy amine R’ C NH2

H NNH 2 2 R hydrazine N hydrazone C NH2 R’

C6H5NH NH2 R H phenylhydrazine NNC phenylhydrazone R’ C6H5

HONH 2 R OH hydroxlamine oxime C N R’ In the above the reactant is RCOR’

Condensation reactions with aldehydes and ketones

condensation polymerization See poly- conducting polymer A type of organic merization. polymer that conducts electricity like a metal. Conducting polymers are crystalline condensation reaction A reaction in substances containing conjugated unsatu- which addition of two molecules occurs rated carbon–carbon bonds. In principle, followed by elimination of a smaller mol- they provide lighter and cheaper alterna- ecule, usually water. Condensation reac- tives to metallic conductors. tions (addition–elimination reactions) are characteristic of aldehydes and ketones re- conductiometric titration /kŏn-duk-tee- acting with a range of nucleophiles. There oh-met-rik/ A titration in which measure- is typically nucleophilic addition at the C ment of the electrical conductance is made atom of the carbonyl group followed by continuously throughout the addition of elimination of water. the titrant and well beyond the equivalence

70 conjugate acid

chair conformation boat conformation

Conformations of cyclohexane

X X X X X

X eclipsed staggered gauche

Conformations for rotation about a single bond

Conformations point. This is in place of traditional end- The ground state electronic configura- point determination by indicators. The op- tion (i.e. the most stable or lowest energy eration is carried out in a conductance cell, state) may then be represented as follows, which is part of a resistance bridge circuit. for example, He, 1s2; N, 1s22s22p5. These The method depends on the fact that ions are identical to the ‘electron box’ models, have different ionic mobilities, H+ and which are often met. However, elements OH– having particularly high values. The are commonly abbreviated by using an method is especially useful for weak inert gas to represent the ‘core’, e.g. Zr has acid–strong base and strong acid–weak the configuration [Kr]4d25s2. base titrations for which color-change 2. The arrangement of atoms or groups in titrations are unreliable. a molecule. configuration /kŏn-fig-yŭ-ray-shŏn/ 1. conformation A particular shape of The arrangement of electrons about the molecule that arises through the normal nucleus of an atom. Configurations are rotation of its atoms or groups about single represented by symbols, which contain: bonds. Any of the possible conformations 1. An integer, which is the value of the that may be produced is called a con- principal quantum number (shell num- former, and there will be an infinite number). ber of these possibilities, differing in the 2. A lower-case letter representing the angle between certain atoms or groups on value of the azimuthal quantum number adjacent carbon atoms. Sometimes, the (l), i.e. term ‘conformer’ is applied more strictly to s means l = 0, p means l = 1, possible conformations that have mini- d means l = 2, f means l = 3. mum energies – as in the case of the boat 3. A numerical superscript giving the num- and chair conformations of CYCLOHEXANE. ber of electrons in that particular set; for example, 1s2, 2p3, 3d5. conjugate acid /kon-jŭ-git/ See acid.

71 conjugate base conjugate base See base. boiling point as the liquid is progressively distilled. The boiling point-composition conjugated /kon-jŭ-gay-tid/ Describing curve shows that distillation of the liquid compounds that have alternating double of composition L1 gives a vapor richer in A and single bonds in their structure. For ex- and represented by composition V1. Fur- ample, but-1,3-ene (H2C:CHCH:CH2) is a ther distillation leads to the liquid compo- typical conjugated compound. In such sition moving towards B. For certain compounds there is delocalization of the mixtures in which there are strong inter- electrons in the double bonds. molecular attractions the boiling point- composition curves show minima or conservation of energy, law of Enun- maxima. Fractional distillation of the for- ciated by Helmholtz in 1847, this law mer leads to initial changes in the vapor states that in all processes occurring in an until a distillate of composition L2 is isolated system the energy of the system re- reached at which point a constant boiling mains constant. The law does of course mixture or AZEOTROPE distills over. Further permit energy to be converted from one attempts to fractionate the distillate do not form to another (including mass, since en- lead to a change in composition. An exam- ergy and mass are equivalent). ple of an azeotropic mixture of minimum boiling point is water (b.p. 100°C) and conservation of mass, law of Formu- ethanol (b.p. 78.3°C), the azeotrope being lated by Lavoisier in 1774, this law states 4.4% water and boiling at 78.1°C. that matter cannot be created or destroyed. Mixtures that display a maximum in Thus in a chemical reaction the total mass the boiling point-composition curve can of the products equals the total mass of the lead to initial separation of pure A on frac- reactants (the term ‘mass’ must include any tionation but as the composition of the liq- solids, liquids, and gases – including air – uid moves towards B and reaches the that participate). maximum, a constant boiling mixture L3 is reached that will distill over unchanged. Constantan /kon-stăn-tan/ (Trademark) An example of an azeotropic mixture of A copper-nickel (cupronickel) alloy con- maximum boiling point is water (b.p. taining 45% nickel. It has a high electrical 100°C) and hydrogen chloride (b.p. resistivity and very low temperature coeffi- –80°C), the azeotrope being 80% water cient of resistance and is therefore used in and boiling at 108.6°C. thermocouples and resistors. constant composition, law of See constant-boiling mixture A general constant proportions; law of. observation for most liquids is that the vapor phase above a liquid is richer in the constant proportions, law of Formu- more volatile component (a deviation from lated by Proust in 1779 after the analysis of Raoult’s law). Consequently most liquid a large number of compounds, the princi- mixtures show a regular increase in the ple that the proportion of each element in

V1 Temperature Temperature Temperature L L L1 2 3 100% A 100% B 100% A 100% B 100% A 100% B

Constant-boiling mixtures

72 copper(I) chloride a compound is fixed or constant. It follows species to another species, which behaves that the composition of a pure chemical as an electron acceptor. The definition in- compound is independent of the method of cludes such examples as the ‘donation’ of preparation. It is also called the law of def- the lone pair of the ammonia molecule to + + 2+ inite proportions and the law of constant H (an acceptor) to form NH4 or to Cu 2+ composition. to form [Cu(NH3)4] . The donor groups are known as Lewis contact process An industrial process bases and the acceptors are either hydro- for the manufacture of sulfuric acid. Sul- gen ions or Lewis acids. Simple combina- → fur(IV) oxide and air are passed over a tions, such as H3N BF3, are known as heated catalyst (vanadium(V) oxide or adducts. See also complex. platinum) and sulfur(VI) oxide is produced: coordination compound /koh-or-dă- → 2SO2 + O2 2SO3 nay-shŏn/ See complex. The sulfur(VI) oxide is dissolved in sulfuric acid coordination number The number of → SO3 + H2SO4 H2S2O7 coordinate bonds formed to a metal atom The resulting oleum is diluted to give sul- or ion in a complex. furic acid. copolymerization /koh-pol-ă-mer-i-zay- continuous phase See colloid. shŏn/ See polymerization. continuous process A manufacturing copper /kopp-er/ A transition metal oc- process in which the raw materials are con- curring in nature principally as the sulfide. stantly fed into the plant. These react as It is extracted by roasting the ore in a con- they flow through the equipment to give a trolled air supply and purified by electroly- continuing flow of product. At any point, sis of copper(II) sulfate solution using only a small amount of material is at a par- impure copper as the anode and pure cop- ticular stage in the process but material at per as the cathode. Copper is used in elec- all stages of the reaction is present. The trical wires and in such alloys as brass and fractional distillation of crude oil is an ex- bronze. ample of a continuous process. Such The metal itself is golden-red in color; processes are relatively easy to automate copper(I) compounds are white (except the and can therefore manufacture a product oxide, which is red), and copper(II) com- cheaply. The disadvantages of continuous pounds are blue in solution. Copper is un- processing are that it usually caters for a reactive to dilute acids (except nitric acid). large demand and the plant is expensive to Copper(I) compounds are unstable in solu- install and cannot normally be used to tion and decompose to copper and cop- make other things. Compare batch per(II) ions. Both copper(I) and copper(II) process. ions form complexes, copper(II) ions being identified by the dark blue complex 2+ continuous spectrum A SPECTRUM [Cu(NH3)4] formed with excess ammo- composed of a continuous range of emitted nia solution. or absorbed radiation. Continuous spectra Symbol: Cu; m.p. 1083.5°C; b.p. are produced in the infrared and visible re- 2567°C; r.d. 8.96 (20°C); p.n. 29; r.a.m. gions by hot solids. 63.546. converter See Bessemer process. copper(II) carbonate (CuCO3) A green crystalline compound that occurs in min- coordinate bond /koh-or-dă-nit/ (dative eral form as the basic salt in azurite and bond) A covalent bond in which the malachite. See also verdigris. bonding pair is visualized as arising from the donation of a lone pair from one copper(I) chloride (cuprous chloride;

73 copper(II) chloride

CuCl) A white solid, insoluble in water, copper(II) sulfate. Copper(I) oxide is easily prepared by heating copper(II) chloride in reduced by hydrogen when heated; it is ox- concentrated hydrochloric acid with excess idized to copper(II) oxide when heated in copper turnings. When the solution is col- air. It is used in the glass industry. Cop- orless, it is poured into air-free water (or per(I) oxide undergoes disproportionation water containing sulfur(IV) oxide) and a in acid solutions, producing copper(II) ions white precipitate of copper(I) chloride is and copper. The oxide will dissolve in con- obtained. On exposure to air this precipi- centrated hydrochloric acid due to the for- – tate turns green due to the formation of mation of the complex ion [CuCl2] . basic copper(II) chloride. Copper(I) chlo- Copper(I) oxide is a covalent solid. ride absorbs carbon monoxide gas. It is used as a catalyst in the rubber industry. copper(II) oxide (cupric oxide; CuO) A The chloride is essentially covalent in black solid prepared by the action of heat structure. In the vapor phase both dimeric on copper(II) nitrate, hydroxide, or car- and trimeric forms exist. It is used in or- bonate. It is a basic oxide and reacts with ganic chemistry in the Sandmeyer reac- dilute acids to form solutions of copper(II) tions. salts. Copper(II) oxide can be reduced to copper by heating in a stream of hydrogen copper(II) chloride (cupric chloride; or carbon monoxide. It can also be reduced CuCl2) A compound prepared by dis- by mixing with carbon and heating the solving excess copper(II) oxide or mixture. Copper(II) oxide is stable up to its copper(II) carbonate in dilute hydrochloric melting point, after which it decomposes to acid. On crystallization, emerald green give oxygen, copper(I) oxide, and eventu- crystals of the dihydrate (CuCl .2H O) are 2 2 ally copper. obtained. The anhydrous chloride may be prepared as a brown solid by burning cop- copper(II) sulfate (cupric sulfate; CuSO ) per in excess chlorine. Alternatively the di- 4 A compound prepared as the hydrate by hydrate may be dehydrated using the action of dilute sulfuric acid on cop- concentrated sulfuric acid. Dilute solutions per(II) oxide or copper(II) carbonate. On of copper(II) chloride are blue, concen- crystallization, blue triclinic crystals of the trated solutions are green, and solutions in the presence of excess hydrochloric acid pentahydrate (blue vitriol, CuSO4.5H2O) are yellow. are formed. Industrially copper(II) sulfate is prepared by passing air through a hot copper(II) nitrate (cupric nitrate; mixture of dilute sulfuric acid and scrap copper. The solution formed is recycled Cu(NO3)2) A compound prepared by dissolving either excess copper(II) oxide or until the concentration of the copper(II) copper(II) carbonate in dilute nitric acid. sulfate is sufficient. Copper(II) sulfate is On crystallization, deep blue crystals of the readily soluble in water. The monohydrate ° trihydrate (Cu(NO ) .3H O) are obtained. (CuSO4.H2O) is formed at 100 C and the 3 2 2 ° The crystals are prismatic in shape and are anhydrous salt at 250 C. Anhydrous cop- extremely deliquescent. On heating, copper(II) sulfate is white; it is extremely hy- per(II) nitrate will decompose to give cop- groscopic and turns blue on absorption of per(II) oxide, nitrogen(IV) oxide, and water. It decomposes on heating to give oxygen. The white anhydrous salt is pre- copper(II) oxide and sulfur(VI) oxide. pared by adding a solution of dinitrogen Copper(II) sulfate is used as a wood pentoxide in nitric acid to crystals of the preservative, a fungicide (in Bordeaux mix- trihydrate. ture), and in the dyeing and electroplating industries. copper(I) oxide (cuprous oxide; CuO) An insoluble red powder prepared by the coral A form of calcium carbonate that heating of copper with copper(II) oxide or is secreted by various invertebrate marine the reduction of an alkaline solution of animals (such as certain members of the

74 creosote class Anthozoa) for support and living covalent bond /koh-vay-lĕnt/ A bond space. formed by the sharing of an electron pair between two atoms. The covalent bond is corn rule See optical activity. conventionally represented as a line, thus H–Cl indicates that between the hydrogen corrosion Reaction of a metal with an atom and the chlorine atom there is an acid, oxygen, or other compound with de- electron pair formed by electrons of oppo- struction of the surface of the metal. Rust- site spin implying that the binding forces ing is a common form of corrosion. are strongly localized between the two atoms. Molecules are combinations of corundum /kŏ-run-dŭm/ (emery; atoms bound together by covalent bonds; Al2O3) A naturally occurring form of covalent bonding energies are of the order 3 –1 aluminum oxide that sometimes contains 10 kJ mol . small amounts of iron and silicon(IV) Modern bonding theory treats the elec- oxide. Ruby and sapphire are impure crys- tron pairing in terms of the interaction of talline forms. It is used in various polishes, electron (atomic) orbitals and describes the abrasives, and grinding wheels. covalent bond in terms of both ‘bonding’ and ‘anti-bonding’ molecular orbitals. coulomb /koo-lom/ Symbol: C The SI unit of electric charge, equal to the charge covalent crystal A crystal in which the transported by an electric current of one atoms present are covalently bonded. They ampere flowing for one second. 1 C = 1 A are sometimes referred to as giant lattices or macromolecules. The best known com- s. The unit is named for the French physi- pletely covalent crystal is diamond. cist Charles Augustin de Coulomb (1736–1806). covalent radius The radius an atom is assumed to have when involved in a cova- coulombmeter /koo-lom-ĕ-ter/ (coulome- lent bond. For homonuclear diatomic mol- ter; voltameter) A device for determining ecules (e.g. Cl ) this is simply half the electric charge or electric current using 2 measured internuclear distance. For het- electrolysis. The mass m of material re- eroatomic molecules substitutional meth- leased in time t is measured and this can be ods are used. For example, the internuclear used to calculate the charge (Q) and the distance of bromine fluoride (BrF) is about current (I) from the electrochemical equiv- 180 pm, therefore using 71 pm for the co- alent (z) of the element, using Q = m/z or I valent radius of fluorine (from F2) we get = m/zt. 109 pm for bromine. The accepted value is 114 pm. coulometer /koo-lom-ĕ-ter/ See coulombmeter. cracking A process whereby petroleum distillates are thermally decomposed to coumarin /koo-mă-rin/ (1,2-benzopyrone; lighter fractions. The process can be purely C9H6O2) A colorless crystalline com- thermal, although catalytic cracking is by pound with a pleasant odor, used in mak- far the most widely used method. ing perfumes. On hydrolysis with sodium hydroxide it forms coumarinic acid. cream of tartar See potassium hydrogentartrate. coumarone /koo-mă-rohn/ See benzfuran. creosote /kree-ŏ-soht/ A colorless oily liquid containing phenols and distilled coupling A chemical reaction in which from wood tar, used as a disinfectant. The two groups or molecules join together. An name is also given to creosote oil, a dark example is the formation of azo com- brown liquid distilled from coal tar and pounds. used for preserving timber. It also consists

75 cresols of phenols, mixed with some methylphe- formula C12H24O6 (six CH2CH2O units). nols. The rings of these compounds are not planar – the name comes from the shape of the cresols /kree-solz, -sohlz/ See methylphe- molecule. The oxygen atoms of these cyclic nols. ethers can coordinate to central metal ions + or to other positive ions (e.g. NH4 ). The critical point The conditions of temper- crown ethers have a number of uses in ature and pressure under which a liquid analysis, separation of mixtures, and as being heated in a closed vessel becomes in- catalysts. Cryptands are similar com- distinguishable from the gas or vapor pounds in which the ether chains are linked phase. At temperatures below the critical by nitrogen atoms to give a three-dimen- temperature (Tc) the substance can be liq- sional cage structure. They are similar in uefied by applying pressure; at tempera- action to crown ethers but generally form tures above Tc this is not possible. For each more strongly bound complexes. See also substance there is one critical point; for ex- host–guest chemistry. ample, for carbon dioxide it is at 31.1°C and 73.0 atmospheres. crude oil See petroleum. critical pressure The lowest pressure cryohydrate /krÿ-oh-hÿ-drayt/A EUTEC- needed to bring about liquefaction of a gas TIC mixture of ice and certain salts. at its critical temperature. cryolite /krÿ-ŏ-lÿt/ See sodium hexafluo- critical temperature The temperature roaluminate. below which a gas can be liquefied by applying pressure and above which no cryoscopic constant /krÿ-ŏ-skop-ik/ See amount of pressure is sufficient to bring depression of freezing point. about liquefaction. Some gases have critical temperatures above room temperature cryptands /krip-tandz/ See crown (e.g. carbon dioxide 31.1°C and chlorine ethers. 144°C) and have been known in the liquid state for many years. Liquefaction proved crystal A solid substance that has a def- much more difficult for those gases (e.g. inite geometric shape. A crystal has fixed oxygen –118°C and nitrogen –146°C) that angles between its faces, which have dis- have very low critical temperatures. tinct edges. The crystal will sparkle if the faces are able to reflect light. The constant critical volume The volume of one angles are caused by the regular arrange- mole of a substance at its critical point. ments of particles (atoms, ions, or molecules) in the crystal. If broken, a large crossed-beam reaction A chemical recrystal will form smaller crystals. action performed with two molecular In crystals, the atoms, ions, or mol- beams intersecting at an angle. Crossed- ecules of the substance form a distinct reg- beam reactions usually involve very simple ular array in the solid state. The faces and reactions at low pressures. The products their angles bear a definite relationship to are detected by mass spectroscopy and fun- the arrangement of these particles. damental information can be obtained about reaction mechanisms. crystal-field theory A theory of the properties of metal COMPLEXES. Originally cross linkage An atom or short chain it was introduced by Hans Bethe in 1929 to joining two longer chains in a polymer. account for the properties of transition elements in ionic crystals. In the theory, the crown ether A compound that has a ligands surrounding the metal atom or ion large ring composed of –CH2–CH2–O– are thought of as negative charges, and the units. For example, 18-crown-6 has the effect of these charges on the energies of

76 crystallization

Cubic crystal structures

face-centered

body-centered simple cubic the d orbitals of the central metal ion is instance, lead (and other metals) are crys- considered. Crystal-field theory was suc- talline. Such substances are composed of cessful in describing the spectroscopic, accumulations of tiny crystals. Compare magnetic, and other properties of com- amorphous. plexes. It has been superseded by ligand- field theory, in which the overlap of the d crystallite /kris-tă-lÿt/ A small crystal orbitals on the metal ion with orbitals on that has the potential to grow larger. It is the ligands is taken into account. often used in mineralogy to describe specimens that contain accumulations of many crystal habit The shape of a crystal. The minute crystals of unknown chemical com- habit depends on the way in which the crystal has grown; i.e. the relative rates of position and crystal structure. development of different faces. crystallization /kris-tă-li-zay-shŏn/ The crystalline /kris-tă-lin, -lÿn/ Denoting a process of forming crystals. When a sub- substance that forms crystals. Crystalline stance cools from the gaseous or liquid substances have a regular internal arrange- state to the solid state, crystallization oc- ment of atoms, even though they may not curs. Crystals will also form from a solu- exist as geometrically regular crystals. For tion saturated with a solute.

77 crystallography crystallography /kris-tă-log-ră-fee/ The propene over a phosphoric acid catalyst study of the formation, structure, and (250°C and 30 atmospheres): → properties of crystals. See also x-ray crys- C6H6 + CH2:CH(CH3) tallography. C6H5CH(CH3)2 The isopropylbenzene is oxidized by air to crystalloid /kris-tă-loid/ A substance a ‘hydroperoxide’: that is not a colloid and which will there- C6H5C(CH3)2–O–O–H fore not pass through a semipermeable This is hydrolyzed by dilute acid to phenol membrane. See colloid; semipermeable (C6H5OH) and propanone (CH3COCH3), membrane. which is a valuable by-product. crystal structure The particular repeat- cupellation /kyoo-pe-lay-shŏn/ A tech- ing arrangement of atoms (molecules or nique used for the separation of silver ions) in a crystal. ‘Structure’ refers to the and/or gold from impurities by the use of internal arrangement of particles, not the an easily oxidizable metal, such as lead. external appearance. The impure metal is heated in a furnace and a blast of hot air is directed upon it. crystal system A classification of crys- The lead or other metal forms an oxide, tals based on the shapes of their unit cell. If leaving the silver or gold behind. the unit cell is a parallelopiped with lengths a, b, and c and the angles between these cupric chloride /kyoo-prik/ See cop- edges are α (between b and c), β (between per(II) chloride. a and c), and γ (between a and b), then the classification is: cubic: a = b = c; α = β = γ cupric nitrate See copper(II) nitrate. = 90° tetragonal: a = b ≠ c; α = β = γ = 90° orthorhombic: a ≠ b ≠ c; α = β = γ = 90° cupric oxide See copper(II) oxide. hexagonal: a = b ≠ c; α = β = 90°; γ = 120° trigonal: a = b ≠ c; α = β = γ≠90° mono- cupric sulfate See copper(II) sulfate. clinic: a ≠ b ≠ c; α = γ = 90°≠βtriclinic: a ≠ b ≠ c; α≠β≠γ /kyoo-prÿt/ A red mineral form The orthorhombic system is also called the cuprite rhombic system. of copper(I) oxide (Cu2O), a principal ore of copper. CS gas ((2-chlorobenzylidine-)-malanoni- cupronickel /kyoo-prŏ-nik-ăl/ A series trile; C6H4ClCH:C(CN)2) A white organic compound that is a nasal irritant of strong copper-nickel alloys containing used in powder form as a tear gas for riot up to 45% nickel. Those containing 20% control. and 30% nickel are very malleable, can be worked cold or hot, and are very corro- cubic Denoting a crystal in which the sion-resistant. They are used, for example, unit cell is a cube. In a simple cubic crystal in condenser tubes in power stations. the particles are arranged at the corners of Cupronickel with 25% nickel is widely a cube. See also body-centered cubic crys- used in coinage. See also Constantan. tal; face-centered cubic crystal; crystal system. cuprous chloride /kyoo-prŭs/ See copper(I) chloride. cubic close packed See face-centered cubic crystal. cuprous oxide See copper(I) oxide. cumene process /kyoo-meen/ An indus- curie /kyoo-ree, kyoo-ree/ Symbol: Ci A trial process for the manufacture of phenol unit of radioactivity, equivalent to the from isopropylbenzene (cumene), which is amount of a given radioactive substance itself made by passing benzene vapor and that produces 3.7 × 1010 disintegrations

78 cycloalkane per second, the number of disintegrations (K3Fe(CN)6, potassium ferricyanide) is an produced by one gram of radium. orange crystalline compound. Its solution gives a deep blue precipitate with iron(II) curium /kyoo-ree-ŭm/ A highly toxic ra- ions, and is used as a test for iron(II) (fer- dioactive silvery element of the actinoid se- rous) compounds. Prassian blue is a blue ries of metals. A transuranic element, it is pigment containing hexacyanoferrate ions. not found naturally on Earth but is synthesized from plutonium. Curium-244 and cyanogen /sÿ-an-ŏ-jen/ (C2N2) A toxic curium-242 have been used in thermoelec- flammable gas prepared by heating mer- tric power generators. cury cyanide. See also pseudohalogens. Symbol: Cm; m.p. 1340±40°C; b.p. ≅ 3550°C; r.d. 13.3 (20°C); p.n. 96; most cyanohydrin /sÿ-an-oh-hÿ-drin/ An ad- stable isotope 247Cm (half-life 1.56 × 107 dition compound formed between an alde- years). The unit is named for the French hyde or ketone and hydrogen cyanide. The physicist Pierre Curie (1859–1906). general formula is RCH(OH)(CN) (from an aldehyde) or RR′C(OH)(CN) (from a cyanamide process /sÿ-an-ă-mÿd, -mid, ketone). Cyanohydrins are easily hy- sÿ-ă-nam-ÿd, -id/ An industrial process drolyzed to hydroxycarboxylic acids. For for fixing nitrogen by heating calcium di- instance, the compound 2-hydrox- carbide in air. ypropanonitrile (CH3CH(OH)(CN)) is hy- → drolyzed to 2-hydroxypropanoic acid CaC2 + N2 CaCN2 The product, calcium cyanamide, hy- (CH3CH(OH)(COOH)). drolyzes to ammonia and can be used as a fertilizer. The process is expensive due to the high cost of calcium dicarbide. See also R OH nitrogen fixation. C cyanide /sÿ-ă-nÿd, -nid/ 1. A salt of hy- H CN drogen cyanide, containing the cyanide ion from aldehyde (CN–). See hydrocyanic acid. 2. See nitrile. R OH C cyanide process A technique used for R’ CN the extraction of gold from its ores. After from ketone crushing the gold ore to a fine powder it is agitated with a very dilute solution of Cyanohydrins potassium cyanide. The gold is dissolved by the cyanide to form potassium di- cyclic compound A compound con- cyanoaurate(I) (potassium aurocyanide, taining a ring of atoms. If the atoms form- KAu(CN)2). This complex is reduced with ing the ring are all the same the compound zinc, filtered, and melted to obtain the pure is homocyclic; if different atoms are ingold metal. volved it is heterocyclic. cyanoferrate /sÿ-an-oh-fe-rayt/ A com- cyclization /sÿ-kli-zay-shŏn/ A reaction 4– pound containing the ion [Fe(CN)6] (the in which a straight-chain compound is con- hexacyanoferrate(II) ion) or the ion verted into a cyclic compound. 3– [Fe(CN)6] (the hexacyanoferrate(III) ion). These ions are usually encountered as cycloaddition /sÿ-kloh-ă-dish-ŏn/ See their potassium salts. Potassium hexa- pericyclic reaction. cyanoferrate(II) (K4Fe(CN)6, potassium ferrocyanide) is a yellow crystalline com- cycloalkane /sÿ-kloh-al-kayn/ A satu- pound. Potassium hexacyanoferrate(III) rated cyclic hydrocarbon comprising a ring

79 cyclohexadiene-1,4-dione of carbon atoms, each carrying two hydro- cyclonite /sÿ-klŏ-nÿt, sik-lŏ/ A high ex- gen atoms, general formula CnH2n. Cyclo- plosive made from hexamine. propane (C3H6), and cyclobutane (C4H8) both have strained rings and are highly re- cyclo-octatetraene /sÿ-kloh-ok-tă-tet-ră- active. Other cycloalkanes have similar een/ See annulene. properties to the alkanes, although they are generally less reactive. cyclopentadiene /sÿ-kloh-pen-tă-dÿ- een/ A cyclic hydrocarbon made by cyclohexadiene-1,4-dione /sÿ-kloh- cracking petroleum. The molecules have a heks-ă-dÿ-een, -dÿ-ohn/ See quinone. five-membered ring containing two carbon-carbon double bonds and one CH2 cyclohexane /sÿ-kloh-heks-ayn/ (C6H12) group. It forms the negative cyclopentadi- – A colorless liquid alkane that is commonly enyl ion C5H5 , present in sandwich com- used as a solvent and in the production of pounds, such as ferrocene. hexanedioic acid (adipic acid) for the manufacture of nylon. Cyclohexane, itself, is cyclopentadienyl ion /sÿ-kloh-pen-tă-dÿ- manufactured by the reformation of longer en-ăl/ See cyclopentadiene. chain hydrocarbons present in crude-oil fractions. It is also interesting from a struc- cysteine /sis-tee-een/ See amino acids. tural point of view, existing as a ‘puckered’ six-membered ring, having all bonds be- cytidine /sÿ-tă-din, -deen, -sit-ă-/ (cytosine tween carbon atoms at 109.9° (the tetrahe- nucleoside)A NUCLEOSIDE formed when dral angle). The molecule undergoes rapid cytosine is linked to D-ribose via a β-glyco- interconversion between two ‘chair-like’ sidic bond. CONFORMATIONS, which are energetically equivalent, passing through a ‘boat-like’ cytosine /sÿ-tŏ-sin, -seen/ A nitrogenous structure of higher energy. It is commonly base found in DNA and RNA. Cytosine represented by a hexagon. has the pyrimidine ring structure.

80 D

dalton /dawl-tŏn/ See atomic mass unit. about 1.08 volts; with zinc sulfate it is about 1.10 volts. Dalton’s atomic theory /dawl-tŏnz/ A At the copper electrode copper ions in theory explaining the formation of com- solution gain electrons from the metal and pounds by elements first published by John are deposited as copper atoms: Dalton in 1803. It was the first modern at- Cu2+ + 2e– → Cu tempt to describe chemical behavior in The copper electrode thus gains a posi- terms of atoms. The theory was based on tive charge. At the zinc electrode, zinc certain postulates: atoms from the electrode lose electrons and 1. All elements are composed of small par- dissolve into solution as zinc ions, leaving ticles, which Dalton called atoms. a net negative charge on the electrode 2. All atoms of the same element are iden- Zn → 2e– + Zn2+ tical. The cell is named for the British chemist 3. Atoms can neither be created nor de- and meteorologist John Frederic Daniell stroyed. (1790–1845). 4. Atoms combine to form ‘compound atoms’ (i.e. molecules) in simple ratios. darmstadtium /darm-stat-ee-ŭm. -shtat-/ Dalton also suggested symbols for the A radioactive metallic element that does elements. The theory was used to explain not occur naturally on the Earth. It is made the law of conservation of mass and the either by bombarding a lead target with laws of chemical combination. The theory nickel nuclei or by bombarding a pluto- is named for the British chemist and physi- nium target with sulfur nuclei. There are cist John Dalton (1766–1844). several isotopes; the most stable is 281Ds, with a half-life of about 1.6 minutes. The Dalton’s law (of partial pressures) The chemical properties of darmstadtium pressure of a mixture of gases is the sum of should be similar to those of platinum. the partial pressures of each individual The element is named for Darmstadt, constituent. (The partial pressure of a gas the place in Germany where it was disin a mixture is the pressure that it would covered. exert if it alone were present in the con- Symbol Ds; p.n. 110. tainer.) Dalton’s law is strictly true only for ideal gases. dative bond /day-tiv/ See coordinate bond. Daniell cell /dan-yĕl/ A type of primary cell consisting of two electrodes in different Davy lamp /day-vee/ See safety lamp. electrolytes separated by a porous partition. The positive eletrode is copper im- d-block elements The TRANSITION EL- mersed in copper(II) sulfate solution. The EMENTS of the first, second, and third long negative electrode is zinc–mercury amal- periods of the periodic table, i.e. Sc to Zn, gam in either dilute sulfuric acid or zinc Y to Cd, and La to Hg. They are so called sulfate solution. The porous pot prevents because in general they have inner d-levels mixing of the electrolytes, but allows ions with configurations of the type (n – 1)dxns2 to pass. With sulfuric acid the e.m.f. is where x = 1–10.

81 DDT

DDT /dee-dee-tee/ (dichlorodiphenyl- decahydrate /dek-ă-hÿ-drayt/ A crys- trichloroethane; (ClC6H4)2CH(CCl3)) A talline solid containing ten molecules of colorless crystalline organic compound, water of crystallization per molecule of once widely used as an insecticide. Its use is compound. now restricted or banned in many countries because it is stable and remains un- decant /di-kant/ To pour off the clear liq- changed in the soil, and passes up the food uid above a sediment. chain to accumulate in the fatty tissues of carnivorous animals. decay 1. The spontaneous breakdown of a radioactive isotope. See half-life; radioac- deactivation A process in which the reactivity. tivity of a substance is lessened, or even to- 2. The transition of excited atoms, ions, tally removed . Usually this deactivation is molecules, etc., to the ground state. unwanted, as in the poisoning of catalysts. deci- Symbol: d A prefix denoting 10–1. de Broglie wave /dĕ-broh-lyee/ A wave For example, 1 decimeter (dm) = 10–1 associated with a particle, such as an elec- meter (m). tron or proton. In 1924, Louis de Broglie suggested that, since electromagnetic decomposition A chemical reaction in waves can be described as particles (pho- which a compound is broken down into tons), particles of matter could also have compounds with simpler molecules. wave properties. The wavelength (λ) has the same relationship to momentum (p) as decrepitation /di-krep-ă-tay-shŏn/ Heat- in electromagnetic radiation: ing a crystalline solid so that it emits a λ = h/p crackling noise, usually as a result of loss of where h is the Planck constant. The wave is water of crystallization. named for the French physicist Prince Louis Victor Pierre Raymond de Broglie defect An irregularity in the ordered (1882–1987). See also quantum theory. arrangement of particles in a crystal lattice. There are two main types of defect in crys- debye /dĕ-bay-ĕ/ Symbol: D A unit of elec- tals. Point defects occur at single lattice tric dipole moment equal to 3.335 64 × points and there are two types. A vacancy 10–30 coulomb meter. It is used in express- is a missing atom; i.e. a vacant lattice point. ing the dipole moments of molecules. the Vacancies are sometimes called Schottky unit is named for the Dutch–American defects (named for the Swiss–German physicist Peter Joseph William Debye physicist Walter Schottky (1886–1976). (1884–1966). An interstitial is an atom that is in a position that is not a normal lattice point. If an Debye–Hückel theory /dĕ-bay-ĕ hoo-kĕl/ atom moves off its lattice point to an inter- A theory to predict the conductivity of ions stitial position the result (vacancy plus in- in dilute solutions of strong ELECTROLYTES. terstitial) is a Frenkel defect (named for the It assumes that electrolytes in dilute solu- Russian mathematical physicist Jacov Il- tion are completely dissociated into ions l’ich Frenkel (1894–1952). All solids above but takes into account interionic attraction absolute zero have a number of point de- and repulsion. Agreement between the the- fects, the concentration of defects depend- ory and experiment occurs only with very ing on the temperature. Point defects can dilute solutions (less than 10–3M). See dis- also be produced by strain or by irradia- sociation. tion. Dislocations (or line defects) are also deca- Symbol: da A prefix denoting 10. produced by strain in solids. They are ir- For example, 1 decameter (dam) = 10 me- regularities extending over a number of lat- ters (m). tice points along a line of atoms.

82 delta metal definite proportions, law of See con- The molar energy of a gas is the average stant proportions; law of. energy per molecule multiplied by the Avo- gadro constant. For a monatomic gas it is degassing Removal of dissolved or ab- 3RT/2, etc. sorbed gases from liquids or solids. 2. The independent physical quantities (e.g. pressure, temperature, etc.) that de- degenerate Describing different quantum fine the state of a given system. See phase states that have the same energy. For in- rule. stance, the five d orbitals in a transition- metal atom all have the same energy but dehydration /dee-hÿ-dray-shŏn/ 1. Re- different values of the magnetic quantum moval of water from a substance. number m. Differences in energy occur if a 2. Removal of the elements of water (i.e. magnetic field is applied or if the arrange- hydrogen and oxygen in a 2:1 ratio) to ment of ligands around the atom is not form a new compound. An example is the symmetrical. The degeneracy is then said dehydration of propanol to propene over to be ‘lifted’. hot pumice: → C3H7OH CH3CH:CH2 + H2O degradation A chemical reaction involving the decomposition of a molecule into deionization /dee-ÿ-ŏ-ni-zay-shŏn/ A simpler molecules, usually in stages. The method of removing ions from a solution Hofmann degradation of amides is an ex- using ION EXCHANGE. The term is com- ample. monly applied to the purification of tap water; deionized water has superseded dis- degrees of freedom 1. The independent tilled water in many chemical applications. ways in which particles can take up energy. /del-ă-kwess-ĕnt/ Describing In a monatomic gas, such as helium or deliquescent a solid compound that absorbs water from argon, the atoms have three translational the atmosphere, eventually forming a solu- degrees of freedom (corresponding to motion. See also hygroscopic. tion in three mutually perpendicular directions). The mean energy per atom for each delocalization /dee-loh-kă-li-zay-shŏn/ A degree of freedom is kT/2, where k is the spreading out of bonding electrons in a Boltzmann constant and T the thermody- molecule over the molecule. namic temperature; the mean energy per atom is thus 3kT/2. delocalized bond /dee-loh-kă-lÿzd/ (non- A diatomic gas also has two rotational localized bond) A type of bonding in mol- degrees of freedom (about two axes per- ecules that occurs in addition to sigma pendicular to the bond) and one vibra- bonding. The electrons forming the delo- tional degree (along the bond). The calized bond are no longer regarded as re- rotations also each contribute kT/2 to the maining between two atoms; i.e. the average energy. The vibration contributes electron density of the delocalized elec- kT (kT/2 for kinetic energy and kT/2 for trons is spread over several atoms and may potential energy). Thus, the average energy spread over the whole molecule. per molecule for a diatomic molecule is The electron density of the delocalized 3kT/2 (translation) + kT (rotation) + kT bond is spread by means of a delocalized (vibration) = 7kT/2. molecular orbital and may be regarded as a Linear triatomic molecules also have series of pi bonds extending over several two significant rotational degrees of free- atoms, for example the pi bonds in butadi- dom; non-linear molecules have three. For ene and the C–O pi bonds in the carbonate non-linear polyatomic molecules, the num- ion. ber of vibrational degrees of freedom is 3N – 6, where N is the number of atoms in the delta metal (delta brass) A strong alloy of molecule. copper and zinc, containing also a little

83 denaturation iron. Its main use is for making cartridge cases. Beckmann thermometer denaturation /dee-nay-chŭ-ray-shŏn/ The changes in structure that occur when a protein is heated. These changes are irre- tube for versible and affect the properties of the introduction protein. of solute denaturing /dee-nay-chŭ-ring/ The process of adding small amounts of conta- container minants to ethanol to make it unfit for for freezing mixture drinking. Denatured alcohol (such as methylated spirits) is not subject to the excise duty on alcoholic drinks. dendritic growth /den-drit-ik/ Growth of crystals in a branching (‘tree-like’) habit. Apparatus for measuring depression of freezing point dendritic polymer See supramolecular polymer. by the presence of a solute. The amount of the reduction is proportional to the molal denitrification /dee-nÿ-tră-fă-kay-shŏn/ concentration of the solute. The depression See nitrogen cycle. depends only on the concentration and is independent of solute composition. The ρ density Symbol: The mass per unit vol- proportionality constant, Kf, is called the ume of a given substance. The units are g freezing point constant or sometimes the –3 ∆ ∆ dm , etc. See also relative density. cryoscopic constant. t = KfCM, where t is the lowering of the temperature and CM is density functional theory A method of the molal concentration; the unit of Kf is calculating the electronic structure of mol- kelvin kilogram mole–1 (K kg mol–1). Al- ecules using the electron density distribu- though closely related to the property of tion in atoms. The theory was developed boiling-point elevation, the cryogenic by Walter Kohn (1923– ) and his col- method can be applied to measurement of leagues in the mid-1960s and has been used relative molecular mass with considerable extensively in chemistry and solid state precision. A known weight of pure solvent physics. is slowly frozen, with stirring, in a suitable cold bath and the freezing temperature deoxyribonucleic acid /dee-oks-ă-rÿ- measured using a Beckmann thermometer. boh-new-klee-ik/ See DNA. A known weight of solute of known molecular mass is introduced, the solvent deoxyribose /dee-oks-ă-rÿ-bohs/ See ri- thawed out, and the cooling process and bose. measurement repeated. The addition is repeated several times and an average value ∆ depolarizer A substance used in a voltaic of Kf for the solvent obtained by plotting t cell to prevent polarization. Hydrogen against CM. The whole process is then re- bubbles forming on the electrode can be repeated using the unknown solute and its moved by an oxidizing agent, such as man- relative molecular mass determined using ganese(IV) oxide. the value of Kf previously obtained. The effect is applied to more precise depression of freezing point A colliga- measurement of relative molecular mass by tive property of solutions in which the using a pair of Dewar flasks (pure solvent freezing point of a given solvent is lowered and solution) and measuring ∆t by means

84 detergents of thermocouples. The theoretical explana- destructive distillation The process of tion is similar to that for LOWERING OF heating an organic substance such that it VAPOR PRESSURE. The freezing point of the wholly or partially decomposes in the ab- solvent is that point at which the curve rep- sence of air to produce volatile products, resenting the vapor pressure above the liq- which are subsequently condensed. The de- uid phase intersects the curve representing structive distillation of coal was the the vapor pressure above the frozen sol- process for manufacturing coal gas and vent. The addition of solute depresses the coal tar. Formerly, methanol was made by former curve but as the solid phase that the destructive distillation of wood. separates is always pure solvent (above the eutectic point), there is no attendant de- detergents A group of substances that im- pression of the latter curve. Consequently prove the cleansing action of solvents, par- the point of intersection is depressed, re- ticularly water. The majority of detergents, sulting in a lowering of the freezing point. including soap, have the same basic structure. Their molecules have a hydrocarbon derivative A compound obtained by reac- chain (tail) that does not attract water mol- tion from another compound. The term is ecules. The tail is said to be hydrophobic most often used in organic chemistry of (water hating). Attached to this tail is a compounds that have the same general small group (head) that readily ionizes and structure as the parent compound. attracts water molecules. It is said to be hydrophilic (water loving). Detergents reduce derived unit A unit defined in terms of the surface tension of water and thus improve its wetting power. Because the deter- base units, and not directly from a stan- gent ions have their hydrophilic heads dard value of the quantity it measures. For anchored in the water and their hydropho- example, the newton is a unit of force de- bic tails protruding above it, the water sur- fined as a kilogram meter second–2 (kg m face is broken up, enabling the water to s–2). See also SI units. spread over the material to be cleaned and penetrate between the material and the desalination /dee-sal-ă-nay-shŏn/ Any of dirt. With the assistance of agitation, the various techniques for removing the salts dirt can be floated off. The hydrophobic (mainly sodium chloride) from sea water to tails of the detergent molecules ‘dissolve’ in make it fit for drinking, irrigation, use in grease and oils. The protruding hy- water-cooled engines, and for making drophilic heads repel each other causing steam for steam turbines. There are various the oil to roll up and form a drop, which methods. Those based on distillation de- floats off into the water as an emulsion. pend on a cheap source of heat energy, of More recently synthetic detergents, often which solar energy is the most promising, derived from petrochemicals, have been especially in hot climates. Flash evapora- developed. Unlike SOAPS these detergents tion (evaporation under reduced pressure) do not form insoluble scums with hard and freezing to make pure ice are other water. methods, as are electrodialysis, ion ex- Synthetic detergents are of three types. change, reverse osmosis, and the use of Anionic detergents form ions consisting of molecular sieves. a hydrocarbon chain to which is attached – either a sulfonate group, –SO2–O , or a – desiccation /dess-ă-kay-shŏn/ Removal of sulfate group, –O–SO2–O . The corre- moisture from a substance. sponding metal salts are soluble in water. Cationic detergents have organic positive + desiccator /dess-ă-kay-ter/ A laboratory ions of the type RNH3 , in which R has a apparatus for drying solids or for keeping long hydrocarbon chain. Non-ionic deter- solids free of moisture. It is a container in gents are complex chemical compounds which is kept a hygroscopic material (e.g. called ethoxylates. They owe their deter- calcium chloride or silica gel). gent properties to the presence of a number

85 deuterated compound of oxygen atoms in one part of the mol- dextrin /deks-trin/ A polysaccharide sugar ecule, which are capable of forming hydro- produced by the action of amylase enzymes gen bonds with the surface water on or the chemical hydrolysis of starch. molecules, thus reducing the surface ten- Dextrins are used as adhesives. sion of the water. dextro-form /deks-troh-form/ See optical deuterated compound A compound in activity. which one or more 1H atoms have been replaced by deuterium (2H) atoms. dextronic acid /deks-tron-ik/ See gluconic acid. deuteride /dew-ter-ÿd/ A compound of deks-troh-roh-tă-tor-ee. - deuterium with other elements; i.e. a hy- dextrorotatory / toh-ree/ See optical activity. dride in which the deuterium isotope is present rather than 1H. See hydride. dextrose /deks-trohs/ (grape-sugar) Natu- rally occurring GLUCOSE belongs to the deuterium /dew-teer-ee-ŭm/ Symbol: D, D 2 stereochemical series and is dextrorota- H A naturally occurring stable isotope of tory, indicated by the symbol (+). Thus the hydrogen in which the nucleus contains term dextrose is used to indicate D-(+)-glu- one proton and one neutron. The atomic cose. As other stereochemical forms of glu- mass is thus approximately twice that of cose have no significance in biological 1H; deuterium is known as ‘heavy hydro- systems the term ‘glucose’ is often used in- gen’. Chemically it behaves almost identi- terchangeably with dextrose in biology. cally to hydrogen, forming analogous compounds, although reactions of deu- d-form See optical activity. terium compounds are often slower than those of the corresponding 1H compounds. D-form See optical activity. This is made use of in kinetic studies where the rate of a reaction may depend on trans- diagonal relationship There is a general fer of a hydrogen atom (i.e. a kinetic iso- trend in the periodic table for electronega- tope effect). tivity to increase from left to right along a period and decrease down a group. Thus a move of ‘one across and one down’, i.e. a deuterium oxide (D2O) The chemical name of heavy water. See deuterium. diagonal move in the table, gives rise to effects that tend to cancel each other. There deuteron /dew-ter-on/ The nucleus of the is a similar combined effect for size, which deuterium atom, 2H+. decreases along a period but increases down a group. This diagonal relationship gives rise to similarities in chemical proper- Dewar flask /dew-er/ (vacuum flask) A ties, which are particularly noticeable for double-walled container of thin glass with the following pairs: Li–Mg; Be–Al; B–Si. the space between the walls evacuated and Li–Mg: sealed to stop conduction and convection 1. both have carbonates that give CO2 on of energy through it. The glass is often sil- heating; vered to reduce radiation. 2. both burn in air to give the normal oxide only; Dewar structure A representation of the 3. both form a nitride; structure of BENZENE in which there is a sin- 4. both form hydrated chlorides that hy- gle bond between two opposite corners of drolyze slowly. the hexagonal ring and two double bonds Be–Al: at the sides of the ring. The Dewar struc- 1. both give hydrogen with alkalis; tures contribute to the resonance hybrid of 2. both give water-insoluble hydroxides benzene. that dissolve in alkali;

86 dibasic acid

3. both form complex ions of the type (H2), oxygen (O2), nitrogen (N2), and the – MCl3 ; halogens are examples of diatomic ele- 4. both have covalently bridged chlorides. ments. B–Si: 1. both form acidic oxides of a giant cova- diatomite /dÿ-at-ŏ-mÿt/ (diatomaceous lent-molecule type with high melting earth; kieselguhr) A whitish powdered points; mineral consisting mainly of silica (sili- 2. both form low-stability hydrides that ig- con(IV) oxide) derived from the shells of nite in air; diatoms. It is used to make fireproof ce- 3. both form readily hydrolyzable chlo- ments and as an absorbent in the manufac- rides that fume in air; ture of DYNAMITE. 4. both have amorphous and crystalline forms and both form glasses with basic diazine /dÿ-ă-zeen, -zin/ See pyrazine. oxides, such as Na2O. diazole /dÿ-ă-zohl, dÿ-ay-/ See pyrazole. diamagnetism /dÿ-ă-mag-nĕ-tiz-ăm/ See magnetism. diazonium salt /dÿ-ă-zoh-nee-ŭm/ A + – compound of the type RN2 X , where R is 1,6-diaminohexane /dÿ-am-ă-noh-heks- an aromatic group and X– a negative ion. ayn/ (hexamethylene diamine; H2N(CH2)6- Diazonium salts are made by diazotization. NH2) An organic compound used as a They can be isolated but are very unstable, starting material in the production of and are usually prepared in solution. The + NYLON. It is manufactured from cyclo- –N2 group renders the benzene ring sus- hexane. ceptible to nucleophilic substitution (rather than electrophilic substitution). Typical re- diamond An allotrope of CARBON. It is the actions are: hardest naturally occurring substance and 1. Reaction with water on warming the so- is used for jewelry and, industrially, for lution: + → + cutting and drilling equipment. Each car- RN2 + H2O ROH + N2 + H bon atom is surrounded by four equally 2. Reaction with halogen ions (CuCl cata- spaced carbon atoms arranged tetrahe- lyst for chloride ions): + – → drally. The carbon atoms form a three-di- RN2 + I RI + N2 mensional network with each Diazonium ions can also act as elec- carbon–carbon bond equal to 0.154 nm trophiles and substitute other benzene and at an angle of 109.5° with its neigh- rings (diazo coupling). See azo compound. bors. In diamonds millions of atoms are covalently bonded to form a giant molecular diazotization /dÿ-a-zŏ-ti-zay-shŏn/ The structure, the great strength of which re- reaction of an aromatic amine (e.g. aniline) sults from the strong covalent bonds. Dia- with nitrous acid at low temperatures monds can be formed synthetically from (below 5°C). → + – graphite in the presence of a catalyst and C6H5NH2 + HNO2 C6H5N N + OH under extreme temperature and pressure; + H2O although small, such diamonds are of ade- The acid is prepared in situ by reaction be- quate size for many industrial uses. tween nitric acid and sodium nitrite. The resulting diazonium ion is susceptible to at- diastereoisomer See isomerism. tack by nucleophiles and provides a method of nucleophilic substitution onto diatomaceous earth /dÿ-ă-tŏ-may-shŭs/ the benzene ring. See diatomite. dibasic acid /dÿ-bay-sik/ An acid which diatomic /dÿ-ă-tom-ik/ Describing a mol- has two active protons, such as sulfuric ecule that consists of two atoms. Hydrogen acid. Dibasic acids can give rise to two se-

87 1,2-dibromoethane

H H

H C H H COOH H C COOH C C C C

C C C C H C H H COOH H C COOH

H H

butadiene maleic acid phthalic acid

Diels–Alder reaction

ε ries of salts. For example, sulfuric acid tive permittivity) Symbol: r A quantity 2– (H2SO4) forms sulfates (SO4 ) and hydro- that characterizes how a medium reduces – gensulfates (HSO 4). the electric field strength associated with a distribution of electric charges. If two 1,2-dibromoethane /dÿ-broh-moh-eth- point charges Q1 and Q2 are a distance d ε ayn/ (ethylene dibromide; BrCH2CH2Br) apart in a medium with a permittivity this A colorless volatile organic liquid, made by means that the force F between the charges πε 2 reacting bromine with ethene. It is used as is given by F = (1/4 )(Q1Q2/d ). a fuel additive to remove lead (as lead bro- The dielectric constant of the medium is ε ε ε ε mide, which is also volatile). See also lead given by r = / 0, where 0 is the permittiv- tetraethyl. ity of free space. The dielectric constant of air is very slightly greater than 1, while that dicarbide /dÿ-kar-bÿd/ See carbide. of water is about 80. The value of the dielectric constant of a medium has impor- dicarboxylic acid /dÿ-kar-boks-il-ik/ An tant physical and chemical consequences, organic acid that has two carboxyl groups particularly for ions in solutions. (–COOH). An example is hexanedioic acid, HOOC(CH2)4COOH (adipic acid). Diels–Alder reaction /deelz awl-der/ An organic addition reaction used to make six- dichlorine oxide /dÿ-klor-een, -in, -kloh- membered ring compounds. A CONJUGATED reen, -rin/ (chlorine monoxide; Cl2O) An compound (a compound with two double orange gas made by passing chlorine over bonds separated by a single bond, such as mercury(II) oxide. It is a strong oxidizing a diene) adds to a compound with a single agent and dissolves in water to give chlo- double bond to form the six-membered ric(I) acid. ring. The reaction is named for the German organic chemists Otto Paul Herman Diels dichloroacetic acid /dÿ-klor-oh-ă-see-tik, (1876–1954) and Kurt Alder (1902–58). -set-ik, -kloh-roh-/ See chloroethanoic acid. diene /dÿ-een/ An organic compound containing two carbon–carbon double bonds. dichloroethanoic acid /dÿ-kor-oh-eth-ă- noh-ik, -kloh-roh-/ See chloroethanoic diesel fuel /dee-zĕl/ A petroleum fraction acid. consisting of various alkanes in the boiling range 200–350°C, used as a fuel for diesel dichromate(VI) /dÿ-kroh-mayt/ A salt (compression-ignition) engines. – containing the ion Cr2O7 . Dichromates are strong oxidizing agents. See potassium diethyl ether /dÿ-eth-ăl/ See ethoxy- dichromate. ethane. dielectric constant /dÿ-i-lek-trik/ (rela- diffusion /di-fyoo-zhŏn/ Movement of a

88 2,4-dinitrophenylhydrazine gas, liquid, or solid as a result of the ran- dimer /dÿ-mer/ A compound (or mol- dom thermal motion of its particles (atoms ecule) formed by combination or associa- or molecules). A drop of ink in water, for tion of two molecules of a monomer. For example, will slowly spread throughout instance, aluminum chloride (AlCl3) is a the liquid. Diffusion in solids occurs very dimer (Al2Cl6) in the vapor. slowly at normal temperatures. See also Graham’s law. dimesoiodic (VII) acid /dÿ-mess-oh-ÿ- od-ik/ See iodic (VII) acid. dihydrate /dÿ-hÿ-drayt/ A crystalline compound with two molecules of water of dimethylbenzene /dÿ-meth-ăl-ben-zeen, crystallization per molecule of compound. ben-zeen/ (xylene; C6H4(CH3)2) An organic hydrocarbon present in the light-oil dihydric alcohol /dÿ-hÿ-drik/ See diol. fraction of crude oil. It is used extensively as a solvent. There are three isomeric com- 2,3-dihydroxybutanedioic acid /dÿ-hÿ- pounds with this name and formula, droks-ăl-byoo-tayn-dÿ-oh-ik/ See tartaric distinguished as 1,2-, 1,3-, and 1,4-di- acid. methylbenzene according to the positions of the methyl groups on the benzene ring. dihydroxypurine /dÿ-hÿ-droks-ă-poor- een, -in/ See xanthine. dimorphism /dÿ-mor-fiz-ăm/ See polymorphism. diiodine hexachloride /dÿ-ÿ-ŏ-deen heks-ă-klor-ÿd, -id, -kloh-rÿd, -kloh-rid / dinitrogen oxide /dÿ-nÿ-trŏ-jĕn/ (nitrous (iodine trichloride; I2Cl6) A yellow crys- oxide; N O) A colorless gas with a faintly talline solid made by reacting excess chlo- 2 sweet odor and taste. It is appreciably sol- rine with iodine. It is a strong oxidizing uble in water (1.3 volumes in 1 volume of agent and at 70°C it dissociates into iodine water at 0°C) but more soluble in ethanol. monochloride and chlorine. It is prepared commercially by the careful heating of ammonium nitrate: dilead(II) lead(IV) oxide /dÿ-led/ (red NH4NO3(s) = N2O(g) + 2H2O(g) lead; Pb3O4) A powder made by heating lead(II) oxide or lead(II) carbonate hydrox- Dinitrogen oxide is fairly easily decom- ° posed on heating to temperatures above ide at 400 C. It is black when hot and red ° or orange when cold. On strong heating it 520 C, giving nitrogen and oxygen. The decomposes to lead(II) oxide and oxygen. gas is used as a mild anesthetic in medicine Dilead(II) lead (IV) oxide is used as a pig- and dentistry, being marketed in small steel ment and in glass making. In practice it cylinders. It is sometimes called laughing tends to have less oxygen than denoted in gas because it induces a feeling of elation the formula. when inhaled. diluent /dil-yoo-ĕnt/ A solvent that is dinitrogen tetroxide /te-troks-ÿd/ (N2O4) added to reduce the strength of a solution. A colorless gas that becomes a pale yellow liquid below 21°C and solidifies below dilute Denoting a solution in which the –11°C. On heating, the gas dissociates to amount of solute is low relative to that of nitrogen dioxide molecules: the solvent. The term is always relative and N2O4(g) = 2NO2(g) includes dilution at trace level as well as the This dissociation is complete at 140°C. common term ‘bench dilute acid’, which Liquid dinitrogen tetroxide has good sol- usually means a 2M solution. Compare vent properties and is used as a nitrating concentrated. agent. dimensionless units The radian and 2,4-dinitrophenylhydrazine /dÿ-nÿ- steradian in SI units. See SI units. troh-fen-ăl-hÿ-dră-zeen/ (Brady’s reagent;

89 diol

µ C6H6N4O4) An orange solid commonly dipole moment Symbol: A quantitative used in solution with methanol and sulfu- measure of polarity in either a bond (bond ric acid to produce crystalline derivatives moment) or a molecule as a whole (molec- by condensation with aldehydes and ke- ular dipole moment). The unit is the debye tones. The derivatives, known as 2,4-dini- (equivalent to 3.34 × 10–30 coulomb trophenylhydrazones, can easily be meter). Molecules such as HF, H2O, NH3, purified by recrystallization and have char- and C6H5NH2 possess dipole moments; acteristic melting points, used to identify CCl4, N2, C6H6, and PF5 do not. the original aldehyde or ketone. The molecular dipole moment can be estimated by vector addition of individual diol /dÿ-ôl/ (dihydric alcohol; glycol) An bond moments if the bond angles are alcohol that has two hydroxyl groups known. The possession of a dipole moment (–OH) per molecule of compound. permits direct interaction with electric fields or interaction with the electric component of radiation. 1,4-dioxan /dÿ-oks-ăn/ ((CH2)2O2) A colorless liquid cyclic ether. It is an inert compound miscible with water used as a dipyridyl /dÿ-pÿ-ră-dăl/ (bipyridyl) A solvent. compound formed by linking two pyridine rings. There are various isomers, some of dioxins /dÿ-oks-inz/ A related group of which are used in herbicides. highly toxic chlorinated compounds. Par- ticularly important is the compound direct dyes A group of dyes that are mostly azo-compounds derived from ben- 2,3,7,8-tetrachlorodibenzo-p-dioxin zidene or benzidene derivatives. They are (TCDD), which is produced as a by-prod- used to dye cotton, viscose rayon, and uct in the manufacture of 2,4,5-T, and may other cellulose fibers directly, using a neu- consequently occur as an impurity in cer- tral bath containing sodium chloride or tain types of weedkiller. The defoliant sodium sulfate as a mordant. known as agent orange used in Vietnam contained significant amounts of TCDD. disaccharide /dÿ-sak-ă-rÿd, -rid/ A SUGAR Dioxins cause a skin disease (chloracne) with molecules composed of two monosac- and birth defects. Dioxins have been re- charide units. Sucrose and maltose are ex- leased into the atmosphere as a result of examples. These are linked by a –O– linkage plosions at herbicide manufacturing (glycosidic link). plants, most notably at Seveso, Italy, in 1976. disconnection See retrosynthetic analysis. diphosphane /dÿ-fos-fayn/ (diphosphine; P2H4) A yellow liquid that can be con- dislocation See defect. densed out from phosphine in a freezing mixture. It ignites spontaneously in air. disodium hydrogen phosphate(V) /dÿ- soh-dee-ŭm/ (disodium hydrogen or- dÿ-fos-feen, -fin diphosphine / / See thophosphate; Na2HPO4) A white solid diphosphane. prepared by titrating phosphoric acid with sodium hydroxide solution using phe- dipolar bond /dÿ-pohl-er/ See coordinate nolphthalein as the indicator. On evapora- bond. tion the solution yields efflorescent monoclinic crystals of the dodecahydrate, dipole /dÿ-pohl/ A system in which two Na2HPO4.12H2O. The effloresced salt equal and opposite electric charges are sep- contains 7H2O. Disodium hydrogen phos- arated by a finite distance. Polar molecules phate is used in the textile industry. have permanent dipoles. Induced dipoles can also occur. See also dipole moment. disodium oxide (sodium monoxide;

90 dissociation constant

Na2O) A highly reactive whitish deliques- cause of the system of valves, they are more cent solid that combines violently with expensive than other types of pump. Com- water to form sodium hydroxide. pare centrifugal pump. disodium tetraborate decahydrate displacement reaction A chemical reac- (borax; Na2B4O7.10H2O) A white crys- tion in which an atom or group displaces talline solid, sparingly soluble in cold another atom or group from a molecule. A water but readily soluble in hot water. It common example is the displacement of occurs naturally as salt deposits in dry lake hydrogen from acids by metals: → beds, especially in California. It is an im- Zn + 2HCl ZnCl2 + H2 portant industrial material, being used in the manufacture of enamels and heat-resis- disproportionation /dis-prŏ-por-shŏ- tant glass, as a paper glaze, etc. nay-shŏn/ A chemical reaction in which Its full systematic name is sodium(I) there is simultaneous oxidation and reduc- heptaoxotetraborate(III)-10-water. In so- tion of the same compound. An example is lution hydrolysis occurs: the reaction of copper(I) chloride to copper 2– – B4O7 + 7H2O = 2OH + 4H3BO3 and copper(II) chloride: The borax-bead test gives characteristic → 2CuCl Cu + CuCl2 colors with certain cations. in which there is simultaneous oxidation (to Cu(II)) and reduction (to Cu(0)). disperse dyes Water-insoluble dyes, Another example is the reaction of which, when held in fine suspension, can chlorine with water: be applied to acetate rayon fabrics. The Cl + H O → 2H+ + Cl– + ClO– dye, together with a dispersing agent, is 2 2 in which there is reduction to Cl– and oxi- warmed to a temperature of 45–50°C and dation to ClO–. the fabric added. By modifying the method of application it is possible to dye poly- dissociation Breakdown of a molecule acrylic and polyester fibers. The yellow/or- into two molecules, atoms, radicals, or ange shades are nitroarylamine derivatives ions. Often the reaction is reversible, as in and the green to bluish shades are deriva- the ionic dissociation of weak acids in tives of 1-amino anthraquinone. Certain water: azo compounds are disperse dyes and these ˆ – CH3COOH + H2O CH3COO + give a range of colors. + H3O disperse phase See colloid. dissociation constant The equilibrium dispersing agent A compound used to as- constant of a dissociation reaction. For ex- sist emulsification or dispersion. ample, the dissociation constant of a reaction: ˆ dispersion force A weak type of inter- AB A + B molecular force. See van der Waals force. is given by: K = [A][B]/[AB] displacement pump A commonly used where the brackets denote concentration device for transporting liquids and gases (activity). around chemical plants. It works on the Often the degree of dissociation is used principle of the bicycle pump: a piston – the fraction (α) of the original compound raises the pressure of the fluid and, when it that has dissociated at equilibrium. For an is high enough, a valve opens and the fluid original amount of AB of n moles in a vol- is discharged through an outlet pipe. As the ume V, the dissociation constant is given piston moves back the pressure falls and by: the cycle continues. Displacement pumps K = α2n/(1 – α)V Note that this can be used to generate very high pressures expression is for dissociation into two (e.g. in the synthesis of ammonia) but be- molecules.

91 distillation

Acid dissociation constants (or acidity dithionous acid /dÿ-th’ÿ-ŏ-nŭs/ (sulfinic constants, symbol: Ka) are dissociation acid; hyposulfurous acid; H2S2O4) An un- constants for the dissociation into ions in stable sulfur oxyacid that is known only in solution: solution. Its salts (dithionites or sulfinates) ˆ + – HA + H2O H3O + A The are powerful reducing agents. concentration of water can be taken as unity, and the acidity constant is given divalent /dÿ-vay-lĕnt/ (bivalent) Having a by: valence of two. + – Ka = [H3O ][A ]/[HA] The acidity constant is a measure of the dl-form See optical activity. strength of the acid. Base dissociation con- D-L convention See optical activity. stants (Kb) are similarly defined. The expression: K = α2n/(1 – α)V DNA (deoxyribonucleic acid) A nucleic applied to an acid is known as Ostwald’s acid, mainly found in the chromosomes, dilution law (named for the German that contains the hereditary information of chemist Friedrich Wilhelm Ostwald organisms. The molecule is made up of two (1853–1932).. In particular if α is small (a antiparallel helical polynucleotide chains weak acid) then K = α2n/V, or α = C√V, coiled around each other to give a double helix. It is also known as the Watson–Crick where C is a constant. The degree of disso- model after James Watson and Francis ciation is then proportional to the square Crick who first proposed this model in root of the dilution. 1953. Phosphate molecules alternate with deoxyribose sugar molecules along both distillation The process of boiling a liquid chains and each sugar molecule is also and condensing the vapor. Distillation is joined to one of four nitrogenous bases – used to purify liquids or to separate com- adenine (A), guanine (G), cytosine (C), or ponents of a liquid mixture. See also de- thymine (T). The two chains are joined to structive distillation; fractional distillation; each other by hydrogen bonding between steam distillation; vacuum distillation. bases. The two purine bases (adenine and guanine) always bond with the pyrimidine distilled water Water that has been puri- bases (thymine and cytosine), and the pair- fied by distillation, perhaps several times. ing is quite specific: adenine with thymine and guanine with cytosine. The two chains disulfur dichloride /dÿ-sul-fer/ (sulfur are therefore complementary. The se- monochloride; S2Cl2) A red fuming liquid quence of bases along the chain makes up with a strong smell. It is prepared by pass- a code – the genetic code – that determines ing chlorine over molten sulfur and is used the precise sequence of amino acids in pro- to harden rubber. teins. DNA is the hereditary material of all diterpene See terpene. organisms with the exception of RNA viruses. See also RNA. dithionate /dÿ-th’ÿ-ŏ-nayt/ A salt of dithionic acid. Döbereiner’s triads /doh-ber-ÿ-nerz/ Tri- ads of chemically similar elements in which dithionic acid /dÿ-th’ÿ-on-ik/ (sulfinic the central member, when placed in order acid; hyposulfuric acid; H2S2O6) A strong of increasing relative atomic mass, has a sulfur oxyacid that decomposes slowly on relative atomic mass approximately equal standing or heating. to the average of the outer two. Other chemical and physical properties of the dithionite /dÿ-th’ÿ-ŏ-nÿt/ (sulfinate) A central member also lie between those of salt of dithionous acid. Dithionites are the first and last members of the triad. The powerful reducing agents. German chemist Johann Wolfgang

92 dubnium

Döbereiner (1780–1849) noted this rela- double salt When equivalent quantities of tionship in 1817; the triads are now recog- certain salts are mixed in aqueous solution nized as consecutive members of a group of and the solution evaporated, a salt may the periodic table; e.g. Ca, Sr, and Ba and form, e.g. FeSO4.(NH4)2SO4.6H2O. In Cl, Br, and I. aqueous solution the salt behaves as a mixture of the two individuals. These salts are dodecanoic acid /doh-dek-ă-noh-ik/ (lau- called double salts to distinguish them ric acid; CH3(CH2)10COOH) A white from complex salts, which yield complex crystalline carboxylic acid, used as a plasti- ions in solution. cizer and for making detergents and soaps. Its glycerides occur naturally in coconut Downs process An electrolytic process and palm oils. for making chlorine from fused sodium chloride. The anode is a central piece of dolomite /dol-ŏ-mÿt/ (pearl spar) A min- graphite, surrounded by a cylindrical steel cathode. A grid and dome between the two eral, CaCO3.MgCO3, used as an ore of magnesium and for the lining of open- keeps the products separate. hearth steel furnaces and Bessemer converters. Dow process /dow/ An industrial method whereby magnesium is extracted from sea- donor 1. The atom, ion, or molecule that water via the precipitation of Mg(OH)2 by provides the pair of electrons in forming a Ca(OH)2, followed by solvation of the pre- covalent bond. cipitated hydroxide by hydrochloric acid. The process is named for the American in- 2. The impurity atoms used in doping semi- dustrial chemist Herbert Henry Dow conductors. (1866–1930), who founded the Dow Chemical Company (1897). doping The incorporation of impurities within the crystal lattice of a solid so as to dry cell A voltaic cell in which the elec- alter its physical properties. For instance, trolyte is in the form of a jelly or paste. The silicon, when doped with boron, becomes Leclanché dry cell is extensively used for semiconducting. flashlights and other portable applications. See also Leclanché cell. double bond A covalent bond between two atoms that includes two pairs of elec- dryers Devices used in chemical processes trons, one pair being the single bond equiv- to remove a liquid from a solid by evapo- alent (the sigma pair) and the other ration. Drying equipment is classified by π forming an additional bond, the pi bond ( the method of transferring heat to a wet bond). It is conventionally represented by solid. This can be by direct contact be- two lines, for example H2C=O. See multi- tween hot gases and the solid (direct dry- ple bond; orbital. ers), heat transfer by conduction through a retaining metallic wall (indirect dryers), or double decomposition (metathesis) A infrared rays (infrared dryers). chemical technique for making an insoluble salt by mixing two soluble salts. The dry ice Solid carbon dioxide, used as a re- ions from the two reactants ‘change part- frigerant. ners’ to form a new soluble compound and the insoluble compound, which is precipi- drying oil A natural oil, such as linseed tated. For example, mixing solutions of oil, that hardens in air. Such oils contain potassium iodide and lead nitrate forms a unsaturated fatty acids, which polymerize solution of potassium nitrate and a yellow on oxidation. precipitate of lead iodide. dubnium /dub-nee-ŭm/ A radioactive syn- double helix See DNA. thetic element made by bombarding 249Cf

93 Dulong and Petit’s law nuclei with 15N atoms. It was first reported 2. A method of finding the amount of ni- by workers at Dubna, a town near trogen in an organic compound by heating Moscow. Symbol: Db; p.n. 105; most sta- the compound with copper oxide to con- ble isotope 262Db (half-life 34 s). vert the nitrogen into nitrogen oxides. These are reduced by passing them over Dulong and Petit’s law /doo-long ănd pĕ- hot copper and the volume of nitrogen col- teez / The molar thermal capacity of a solid lected is measured. element is approximately equal to 3R, where R is the gas constant (25 J K–1 Duralumin /dewr-al-yŭ-min/ (Trademark) mol–1). The law applies only to elements A strong lightweight aluminum alloy con- with simple crystal structures at normal taining 3–4% copper, with small amounts temperatures. At lower temperatures the of magnesium, manganese, and sometimes molar heat capacity falls with decreasing silicon. It is widely used in aircraft bodies. temperature (it is proportional to T3). Molar thermal capacity was formerly dye A coloring material for fabric, leather, called atomic heat – the product of the etc. Most dyes are now synthetic organic atomic weight (relative atomic mass) and compounds (the first such was the dye the specific thermal capacity. The law is mauve synthesized from aniline in 1856 by named for the French physicists Pierre- W. H. Perkin). Dyes are often unsaturated organic compounds containing conjugated Louis Dulong (1785–1838) and Alexis- double bonds – the bond system responsi- Thérèse Petit (1791–1820). ble for the color is called the chromophore. See also azo compound. Dumas’ method /doo-mahz/ 1. A method for determining the vapor densities of dynamite A high explosive made by ab- volatile liquids. The method utilizes a sorbing nitroglycerine into an earthy mate- Dumas bulb; i.e. a glass bulb with a narrow rial such as diatomite (kieselguhr). Solid entrance tube. The bulb is weighed ‘empty’ sticks of dynamite are much safer to handle (i.e. full of air) then the sample is intro- than the highly sensitive liquid nitroglycer- duced and the bulb immersed in a heating ine. bath so that the sample boils and expels all the air. When the surplus vapor has been dyne /dÿn/ Symbol: dyn The former unit expelled, the bulb is sealed off, cooled, of force used in the c.g.s. system. It is equal dried, and weighed. The tip of the tube is to 10–5 N. then broken under water so that the water completely fills the tube and the whole dysprosium /dis-proh-see-ŭm, -shee-ŭm/ weighed again. This enables the volume of A soft malleable silvery element of the lan- the bulb to be calculated from the known thanoid series of metals. It occurs in asso- density of water, and knowing the density ciation with other lanthanoids. One of its of air one can compute the vapor density of few uses is as a neutron absorber in nuclear the sample. The method is named for the reactors; it is also a constituent of certain French chemist Jean Baptiste André Dumas magnetic alloys. (1800–84). See also Hofmann’s method; Symbol: Dy; m.p. 1412°C; b.p. 22562°C; Victor Meyer’s method. r.d. 8.55 (20°C); p.n. 66; r.a.m. 162.50.

94 E

ebulioscopic constant /i-bul-ee-ŏ-skop- Symbol: Es; m.p. 860 ± 30°C; p.n. 99; ik/ See elevation of boiling point. most stable isotope 254Es (half-life 276 days). The element is named for the Ger- ebullition /eb-ŭ-lish-ŏn/ The boiling or man–Swiss–American theoretical physicist bubbling of a liquid. Albert Einstein (1879–1955). eclipsed conformation See conforma- elastomer /i-las-tom-ĕ-ter/ An elastic sub- tion. stance, e.g. a natural or synthetic rubber.

Edison cell See nickel–iron accumulator. electrochemical equivalent /i-lek-trŏ- kem-ă-kăl/ Symbol: z The mass of an el- edta /ee-dee-tee-ay/ (ethylenediamine ement released from a solution of its ion tetraacetic acid) A compound with the for- when a current of one ampere flows for mula one second during electrolysis. (HOOCCH2)2N(CH2)2N(CH2COOH)2 It is used in forming chelates of transition electrochemical series (electromotive se- metals. See chelate. ries) A series giving the activities of metals for reactions that involve ions in solution. effervescence /ef-er-vess-ĕns/ The evolu- In decreasing order of activity, the series is tion of gas in the form of bubbles in a liq- K, Na, Ca, Mg, Al, Zn, Fe uid. Pb, H, Cu, Hg, Ag, Pt, Au Any member of the series will displace efficiency Symbol: η A measure used for ions of a lower member from solution. For processes of energy transfer; the ratio of example, zinc metal will displace Cu2+ the useful energy produced by a system or ions: device to the energy input. For a reversible Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) heat engine, the efficiency is given by Zinc has a greater tendency than copper to η = (T1 – T2)/T1 form positive ions in solution. Similarly, T1 being the source temperature and T2 the metals above hydrogen displace hydrogen ‘sink’ temperature. from acids: → Zn + 2HCl ZnCl2 + H2 efflorescence /ef-flŏ-ress-ĕns/ The process The series is based on electrode potentials, in which a crystalline hydrated solid loses which measure the tendency to form posi- water of crystallization to the air. A pow- tive ions. The series is one of increasing dery deposit is gradually formed. electrode potential for half cells of the type Mn+|M. Thus, copper (EŠ for Cu2+|Cu = + einsteinium /ÿn-stÿ-nee-ŭm/ A radio- 0.34 V) is lower than zinc (EŠ for Zn2+|Zn active transuranic element of the actinoid = –0.76V). The hydrogen half cell has a series, not found naturally on Earth. It can value EŠ = 0. be produced in milligram quantities by bombarding 239Pu with neutrons to give electrochemistry /i-lek-trŏ-kem-iss-tree/ 253Es (half-life 20.47 days). Several other The study of the formation and behavior of short-lived isotopes have been synthesized. ions in solutions. It includes electrolysis

95 electrochromatography and the generation of electricity by chemi- half cell under investigation by a salt cal reactions in cells. bridge. The e.m.f. of the full cell can then be measured. electrochromatography /i-lek-troh-kroh- In referring to a given half cell the more mă-tog-ră-fee/ See electrophoresis. reduced form is written on the right for a half-cell reaction. For the half cell Cu2+|Cu, electrocyclic reaction /i-lek-troh-sÿ-klik/ the half-cell reaction is a reduction: See pericyclic reaction. Cu2+(aq) + 2e → Cu The cell formed in comparison with a hy- electrode Any part of an electrical device drogen electrode is: + 2+ or system that emits or collects electrons or Pt(s)H2(g)|H (aq)|Cu (aq)|Cu other charge carriers. An electrode may The e.m.f. of this cell is +0.34 volt meas- also be used to deflect charged particles by ured under standard conditions. Thus, the the action of the electrostatic field that it standard electrode potential (symbol: EŠ) produces. See also half cell. is +0.34 V for the half cell Cu2+|Cu. The standard conditions are 1.0 molar solu- electrodeposition /i-lek-troh-dep-ŏ-zish- tions of all ionic species, standard pressure, ŏn/ (electroplating) The process of de- and a temperature of 298 K. positing a layer of solid (metal) on an Half cells can also be formed by a solu- electrode by electrolysis. Positive ions in tion of two different ions (e.g. Fe2+ and solution gain electrons at the cathode and Fe3+). In such cases, a platinum electrode is are deposited as atoms. Copper, for in- used under standard conditions. stance, can be deposited on a metal cathode from an acidified copper sulfate electrodialysis /i-lek-troh-dÿ-al-ă-sis/ (pl. solution. electrodialyses) A method of removing ions from water by selective flow through electrode potential Symbol: E A meas- membranes under the influence of an elec- ure of the tendency of an element to form tric field. In a simple arrangement a cell is ions in solution. For example, a metal in a divided into three compartments by two solution containing M+ ions may dissolve semipermeable membranes, one permeable in the solution as M+ ions; the metal then to positive ions and the other permeable to has an excess of electrons and the solution negative ions. Electrodes are placed in the an excess of positive ions – thus, the metal outer compartments of the cell – the posi- becomes negative with respect to the solu- tive electrode next to the membrane that tion. Alternatively, the positive ions may allows negative ions to pass. In this gain electrons from the metal and be de- arrangement, positive and negative ions posited as metal atoms. In this case, the pass through the membranes in leaving metal becomes positively charged with re- deionized water in the center compartment spect to the solution. In either case, a po- of the cell. In practice, an array of alternat- tential difference is developed between ing membranes is used. Electrodialysis is solid and solution, and an equilibrium used for making drinking water in areas in state will be reached at which further reac- which brackish ground water is available. tion is prevented. The equilibrium value of this potential difference would give an in- electrolysis /i-lek-trol-ă-sis/ The produc- dication of the tendency to form aqueous tion of chemical change by passing electric ions. charge through certain conducting liquids It is not, however, possible to measure (electrolytes). The current is conducted by this for an isolated half cell – any measure- migration of ions – positive ones (cations) ment requires a circuit, which sets up an- to the cathode (negative electrode), and other half cell in the solution. Therefore, negative ones (anions) to the anode (posi- electrode potentials (or reduction poten- tive electrode). Reactions take place at the tials) are defined by comparison with a hy- electrodes by transfer of electrons to or drogen half cell, which is connected to the from them.

96 electron affinity

In the electrolysis of water (containing a electrolytic refining A method of purify- small amount of acid to make it conduct ing metals by electrolysis. Copper is puri- adequately) hydrogen gas is given off at the fied by making the impure metal the anode cathode and oxygen is evolved at the in an electrolytic cell with an acidified cop- anode. At the cathode the reaction is: per sulfate electrolyte. The cathode is a thin H+ + e– → H strip of pure copper. The copper at the → 2+ 2H H2 anode dissolves (as Cu ions) and pure At the anode: copper is deposited on the cathode. In this OH– → e– + OH particular process, gold and silver are ob- → 2OH H2O + O tained as by-products, deposited as an → 2O O2 anode sludge on the bottom of the cell. In certain cases the electrode material may dissolve. For instance, in the electrol- electromagnetic radiation Energy prop- ysis of copper(II) sulfate solution with cop- agated by vibrating electric and magnetic per electrodes, copper atoms of the anode fields. Electromagnetic radiation forms a dissolve as copper ions whole electromagnetic spectrum, depend- Cu → 2e– + Cu2+ ing on frequency and ranging from high- See Faraday’s laws. frequency radio waves to low-frequency gamma rays. It can be thought of as waves electrolyte /i-lek-trŏ-lÿt/ A liquid contain- (electromagnetic waves) or as streams of ing positive and negative ions that con- photons. The frequency and wavelength ducts electricity by the flow of those are related by charges. Electrolytes can be solutions of λv = c acids or metal salts (‘ionic compounds’), where c is the speed of light. The energy usually in water. Alternatively they may be carried depends on the frequency. molten ionic compounds – again the ions can move freely through the substance. electromotive series See electrochemical Liquid metals (in which conduction is by series. free electrons rather than ions) are not classified as electrolytes. See also electrolysis. electron /i-lek-tron/ An elementary particle of negative charge (–1.602 192 × electrolytic /i-lek-trŏ-lit-ik/ Relating to 10–19C) and rest mass 9.109 558 × 10–31 the behavior or reactions of ions in solu- kg. Electrons are present in all atoms. tion. electron affinity Symbol: A The energy electrolytic cell See cell; electrolysis. released when an atom (or molecule or group) gains an electron in the gas phase to electrolytic corrosion Corrosion by elec- form a negative ion. It is thus the energy of: trochemical reaction. See rusting. A + e– → A–

ELECTROMAGNETIC SPECTRUM (note: the figures are only approximate)

Radiation Wavelength (m) Frequency (Hz) gamma radiation –10–12 1019– x-rays 10–12–10–9 1017–1020 ultraviolet radiation 10–9 –10–7 1015–1018 visible radiation 10–7 –10–6 1014–1015 infrared radiation 10–6 –10–4 1012–1014 microwaves 10–4 –1 109–1013 radio waves 1 – –109

97 electron-deficient compounds

A positive value of A (often in electron- polar bonds and sometimes to polar mol- volts) indicates that heat is given out. Often ecules. the molar enthalpy is given for this process As the concept of electronegativity is of electron attachment (∆H). Here the not precisely defined it cannot be precisely units are joules per mole (J mol–1), and, by measured and several electronegativity the usual convention, a negative value indi- scales exist. Although the actual values dif- cates that energy is released. fer the scales are in good relative agreement. See also electron affinity; ionization electron-deficient compounds Com- potential. pounds in which the number of electrons available for bonding is insufficient for the electronic energy levels See atom; en- bonds to consist of conventional two-elec- ergy levels. tron covalent bonds. Diborane, B2H6, is an example in which each boron atom has electronic transition The demotion or two terminal hydrogen atoms bound by promotion of an electron between elec- conventional electron-pair bonds and in tronic energy levels in an atom or molecule. addition the molecule has two hydrogen atoms bridging the boron atoms (B–H–B). electron pair Two electrons in one or- In each bridge there are only two electrons bital with opposing spins (spin paired), for the bonding orbital. See also multicen- such as the electrons in a covalent bond or ter bond. lone pair. electron diffraction A technique used to electron spin See atom. determine the structure of substances, principally the shapes of molecules in the electron spin resonance (ESR) A similar gaseous phase. A beam of electrons di- technique to nuclear magnetic resonance, rected through a gas at low pressure pro- but applied to unpaired electrons in a mol- duces a series of concentric rings on a ecule (rather than to the nuclei). It is a photographic plate. The dimensions of powerful method of studying free radicals these rings are related to the interatomic and transition-metal complexes. distances in the molecules. See also x-ray diffraction. electron-transfer reaction A chemical reaction that involves the transfer, addi- electron donor See reduction. tion, or removal of electrons. Many electron-transfer reactions involve complexes electronegative /i-lek-troh-neg-ă-tiv/ De- of transition metals. The rates of such re- scribing an atom or molecule that attracts actions vary enormously and can be ex- electrons, forming negative ions. Examples plained in terms of the way in which of electronegative elements include the molecules of the solvent, which start off halogens (chlorine etc.), which readily solvating the reactants, rearrange so as to form negative ions (F–, Cl–, etc.). See also solvate the products. electronegativity. electronvolt /i-lek-tron-vohlt/ Symbol: eV electronegativity /i-lek-troh-neg-ă-tiv-ă- A unit of energy equal to 1.602 191 7 × tee/ A measure of the tendency of an atom 10–19 joule. It is defined as the energy re- in a molecule to attract electrons to itself. quired to move an electron charge across a Elements to the right-hand side of the peri- potential difference of one volt. It is often odic table are strongly electronegative (val- used to measure the kinetic energies of ele- ues from 2.5 to 4); those on the left-hand mentary particles or ions, or the ionization side have low electronegativities (0.8–1.5) potentials of molecules. and are sometimes called electropositive elements. Different electronegativities of electrophile /i-lek-trŏ-fÿl, -fil/ An elec- atoms in the same molecule give rise to tron-deficient ion or molecule that takes

98 electrum part in an organic reaction. The electrodes) to cause charged particles of a col- trophile can be either a positive ion (H+, loid to move through a solution. The tech- + NO2 ) or a molecule that can accept an nique is used to separate and identify electron pair (SO3, O3). The electrophile colloidal substances such as carbohydrates, attacks negatively charged areas of mol- proteins, and nucleic acids. Various exper- ecules, which usually arise from the pres- imental arrangements are used. One simple ence in the molecule of an electronegative technique uses a strip of adsorbent paper atom or group or of pi-bonds. Compare soaked in a buffer solution with electrodes nucleophile. placed at two points on the paper. This technique is sometimes called electrochro- /i-lek-trŏ-fil-ik/ A electrophilic addition matography. In gel electrophoresis, used to reaction involving the addition of a small separate DNA fragments, the medium is a molecule to an unsaturated organic com- layer of gel. pound, across the atoms held by a double or triple bond. The reaction is initiated by /i-lek-trŏ-play-ting/ The the attack of an electrophile on the elec- electroplating tron-rich area of the molecule. The mecha- process of coating a solid surface with a nism of electrophilic addition is thought to layer of metal by means of electrolysis (i.e. be ionic, as in the addition of HBr to by electrodeposition). ethene: + – → electropositive /i-lek-troh-poz-ă-tiv/ De- H2C:CH2 + H Br + – → scribing an atom or molecule that tends to H3CCH2 + Br H3CCH2Br lose electrons, forming positive ions. Ex- In the case of higher alkenes (more than amples of electropositive elements include two carbon atoms) several isomeric prod- the alkali metals (lithium, sodium, etc.), ucts are possible. The particular isomer which readily form positive ions (Li+, Na+, produced depends on the stability of the al- etc.). ternative intermediates and this is summa- rized empirically by Markovnikoff’s rule. electrovalent bond /i-lek-trŏ-vay-lĕnt/ See also addition reaction. (ionic bond) A binding force between the ions in compounds in which the ions are electrophilic substitution A reaction in- formed by complete transfer of electrons volving substitution of an atom or group of from one element to another element or atoms in an organic compound with an radical. For example, Na + Cl becomes Na+ electrophile as the attacking substituent. + Cl–. The electrovalent bond arises from Electrophilic substitution is very common the excess of the net attractive force be- in aromatic compounds, in which elec- tween the ions of opposite charge over the trophiles are substituted onto the ring. An net repulsive force between ions of like example is the nitration of benzene: charge. The magnitude of electrovalent in- C H + NO + → C H NO + H+ 6 6 2 6 5 2 teractions is of the order 102–103 kJ mol–1 The nitronium ion (NO +) is formed by 2 and electrovalent compounds are generally mixing concentrated nitric and sulfuric acids: solids with rigid lattices of closely packed → + – ions. The strengths of electrovalent bonds HNO3 + H2SO4 H2NO3 + HSO4 + → + vary with the reciprocal of the inter-ionic H2NO3 NO2 + H2O The accepted mechanism for a simple distances and are discussed in terms of lat- electrophilic substitution on benzene in- tice energies. volves an intermediate of the form + i-lek-trŭm C6H5HNO2 . See also substitution reac- electrum / / Originally, a natu- tion. rally occurring alloy of gold and silver (up to 45% silver) that resembles pure gold in electrophoresis /i-lek-troh-fŏ-ree-sis/ The appearance. A synthetic alloy of copper, use of an electric field (between two elec- nickel, and zinc is also known as electrum.

99 element element /el-ĕ-mĕnt/ A substance that can- hahnium (Hn, 108) not be chemically decomposed into more meitnerium (Mt, 109) simple substances. The atoms of an el- The ACU names were: ement all have the same proton num- mendelevium (Md, 101) ber (and thus the same number of nobelium (No, 102) electrons, which determines the chemical lawrencium (Lr, 103) activity). rutherfordium (Rf, 104) At present there are 112 reported chem- hahnium (Ha, 105) ical elements, although research is continu- seaborgium (Sg, 106) ing all the time to synthesize new ones. The nielsbohrium (Ns, 107) elements from hydrogen (p.n. 1) to ura- hassium (Hs, 108) nium (92) all occur naturally, with the ex- meitnerium (Mt, 109) ception of technetium (43), which is A compromise list of names was adopted produced artificially by particle bombard- by IUPAC in 1997: ment. Technetium and elements with pro- mendelevium (Md, 101) ton numbers higher than 84 (polonium) nobelium (No, 102) are radioactive. Radioactive isotopes also lawrencium (Lr, 103) exist for other elements, either naturally in rutherfordium (Rf, 104) small amounts or synthesized by particle dubnium (Db, 105) bombardment. The elements with proton seaborgium (Sg, 106) number higher than 92 are the transuranic bohrium (Bh, 107) elements. Neptunium (93) and plutonium hassium (Hs, 108) (94) both occur naturally in small quanti- meitnerium (Mt, 109) ties in uranium ores, but the transuranics This is the list used in this dictionary. Dub- are all synthesized. Thus, neptunium and nium is named after Dubna in Russia, plutonium are made by neutron bombard- where much work has been done on syn- ment of uranium nuclei. Other transuran- thetic elements. Hassium is the Latin name ics are made by high-energy collision for the German state of Hesse, where the processes between nuclei. The higher pro- German research group is located ton number elements have been detected only in very small quantities – in some In addition to the above elements, seven cases, only a few atoms have been pro- other elements have been reported with duced. proton numbers 110, 111, 112, 113, 114, There has been some controversy about 115, and 116. Element 110 has been the naming of the higher synthetic elements named darmstadtium for the town in Ger- because of disputes about their discovery. many where it was first discovered. El- A long-standing problem concerned element 111 has been named roentgenium ement-104 (rutherfordium) which was for- (for Roentgen). So far the others have not merly also known by its Russian name of been named and have their temporary sys- kurchatovium. More recent confusion has tematic IUPAC names (see unnil-). been caused by differences between names suggested by the International Union of elevation of boiling point A colligative Pure and Applied Chemistry (IUPAC) and property of solutions in which the boiling the names suggested by the American point of a solution is raised relative to that Chemical Union (ACU). of the pure solvent. The elevation is di- The original IUPAC names (1994) were: rectly proportional to the number of solute mendelevium (Md, 101) molecules introduced rather than to any nobelium (No, 102) specific aspect of the solute composition. lawrencium (Lr, 103) The proportionality constant, kB, is called dubnium (Db, 104) the boiling-point elevation constant or joliotium (Jl, 105) sometimes the ebulioscopic constant. The rutherfordium (Rf, 106) relationship is ∆ bohrium (Bh, 107) t = kBCM 100 empirical formula

peratures at which the vapor pressure equals the atmospheric pressure.

Beckmann elimination reaction A reaction involv- thermometer ing the removal of a small molecule, e.g. water or hydrogen chloride, from an or- condenser ganic molecule to give an unsaturated compound. An example is the elimination of a water molecule from an alcohol to produce tube for an alkene. introducing An elimination reaction is often in com- solute petition with a substitution reaction and the predominant product will depend on the reaction conditions. The reaction of bromoethane with sodium hydroxide could yield either ethene (by elimination of HBr) or ethanol (by substitution of the Br with OH). The former product predomi- nates if the reaction is carried out in an alcoholic solution and the latter if the heater solution is aqueous.

Apparatus for measuring elevation Elinvar /el-in-var/ (Trademark) An alloy of boiling point of chromium, iron, and nickel. It is used for making hairsprings for clocks and watches ∆ where t is the rise in boiling point and CM because its elasticity does not vary with is the molal concentration; the units of kB temperature. are kelvins kilograms moles–1 (K kg mol–1). The property permits the measurement of elution /i-loo-shŏn/ The removal of an ad- relative molecular mass of involatile sorbed substance in a chromatography col- solutes. An accurately weighed amount of umn or ion-exchange column using a pure solvent is boiled until the temperature solvent (eluent), giving a solution called the is steady, a known weight of solute of eluate. The chromatography column can known molecular mass is quickly intro- selectively adsorb one or more components duced, the boiling continued, and the ele- from the mixture. To ensure efficient re- vation measured using a Beckmann covery of these components graded elution thermometer. The process is repeated sev- is used. The eluent is changed in a regular manner starting with a non-polar solvent eral times and the average value of k ob- B and gradually replacing it by a more polar tained by plotting ∆t against C . The M one. This will wash the strongly polar com- whole process is then repeated with the un- ponents from the column. See column known material and its relative molecular chromatography. mass obtained using the value of kB previously obtained. emery A mineral form of corundum (alu- There are several disadvantages with minum oxide) with some iron oxide and this method and it is therefore used largely silica impurities. It is extremely hard and is for demonstration purposes. The main used as an abrasive and polishing material. problem is that the exact amount of solvent remaining in the liquid phase is unknown emission spectrum See spectrum. and varies with the rate of boiling. The theoretical explanation of the effect is identi- empirical formula The formula of a cal to that for the lowering of vapor compound showing the simplest ratio of pressure; the boiling points are those tem- the atoms present. The empirical formula

101 emulsion is the formula obtained by experimental given to many different forms of energy analysis of a compound and it can be re- (chemical, electrical, nuclear, etc.); the only lated to a molecular formula only if the real difference lies in the system under dis- molecular weight is known. For example cussion. For example, chemical energy is P2O5 is the empirical formula of phospho- the kinetic and potential energies of elec- rus(V) oxide although its molecular for- trons in a chemical compound. mula is P4O10. Compare molecular formula; structural formula. energy level One of the discrete energies that an atom or molecule, for instance, can emulsion A colloid in which a liquid have according to quantum theory. Thus in phase (small droplets with a diameter an atom there are certain definite orbits –5 –7 range 10 –10 cm) is dispersed or sus- that the electrons can be in, corresponding pended in a liquid medium. Emulsions are to definite electronic energy levels of the classed as lyophobic (solvent-repelling and atom. Similarly, a vibrating or rotating generally unstable) or lyophilic (solvent-at- molecule can have discrete vibrational and tracting and generally stable). rotational energy levels. enantiomer /en-an-tee-ŏ-mer/ (enan- energy profile A diagram that traces the tiomorph) A compound whose structure is changes in the energy of a system during not superimposable on its mirror image: the course of a reaction. Energy profiles are one of any pair of optical isomers. See also obtained by plotting the potential energy isomerism; optical activity. of the reacting particles against the reaction coordinate. To obtain the reaction co- /en-an-tee-ot-rŏ-pee/ The enantiotropy ordinate the energy of the total interacting existence of different stable allotropes of system is plotted against position for the an element at different temperatures; sul- molecules. The reaction coordinate is the fur, for example, exhibits enantiotropy. pathway for which the energy is a mini- The phase diagram for an enantiotropic el- mum. ement has a point at which all the al- The energy profile for the hydrogena- lotropes can coexist in a stable tion of an alkene with and without a cata- equilibrium. At temperatures above or below this point, one of the allotropes will lyst has certain interesting features: the be more stable than the other(s). See also activation energy without the catalyst is allotropy; monotropy. very much larger than that with the catalyst and any point along the horizontal axis enclosure compound See clathrate. represents the changes that the colliding particles experience as atoms are separated endothermic /en-doh-th’er-mik/ Describ- in bond breaking and as atoms are brought ing a process in which heat is absorbed (i.e. together in bond formation. heat flows from outside the system, or the temperature falls). The dissolving of a salt enol /ee-nol, -nohl/ An organic compound in water, for instance, is often an endother- containing the C:CH(OH) group; i.e. one mic process. Compare exothermic. in which a hydroxyl group is attached to the carbon of a double bond. See keto-enol end point See equivalence point; volu- tautomerism. metric analysis. enthalpy /en-thal-pee, en-thal-/ Symbol: H energy Symbol: W A property of a system; The sum of the internal energy (U) and the a measure of its capacity to do work. En- product of pressure (p) and volume (V) of ergy and work have the same unit: the joule a system: (J). It is convenient to divide energy into ki- H = U + pV netic energy (energy of motion) and poten- In a chemical reaction carried out at tial energy (‘stored’ energy). Names are constant pressure, the change in enthalpy

102 equilibrium measured is the internal energy change plus 4. they are inactivated by low concentra- the work done by the volume change: tions of heavy-metal ions. ∆H = ∆U + p∆V epimerism /i-pim-ĕ-riz-ăm/ A form of iso- entropy /en-trŏ-pee/ (pl. entropies) Sym- merism exhibited by carbohydrates in bol: S In any system that undergoes a re- which the isomers (epimers) differ in the versible change, the change of entropy is positions of –OH groups. The α- and β- defined as the heat absorbed divided by the forms of glucose are epimers. See sugar. thermodynamic temperature: δS = δQ/T epoxide /i-poks-ÿd/ A type of organic A given system is said to have a certain en- compound containing a three-membered tropy, although absolute entropies are sel- ring in which two carbon atoms are each dom used: it is change in entropy that is bonded to the same oxygen atom. important. The entropy of a system measures the availability of energy to do work. epoxyethane /i-poks-ee-eth-ayn/ (ethylene In any real (irreversible) change in a oxide; C2H4O) A colorless gaseous ether. closed system the entropy always increases. Epoxyethane has a cyclic structure with a Although the total energy of the system has three-membered ring. It is made by oxida- not changed (first law of thermodynamics) tion of ethene over a silver catalyst. The the available energy is less – a consequence ring is strained and the compound is con- of the second law of thermodynamics. sequently highly reactive. It polymerizes to The concept of entropy has been epoxy polymers (resins). Hydrolysis pro- widened to take in the general idea of dis- duces 1,2-ethanediol. order – the higher the entropy, the more disordered the system. For instance, a chemical reaction involving polymerization may well have a decrease in entropy CH CH because there is a change to a more ordered 2 2 system. The ‘thermal’ definition of entropy O is a special case of this idea of disorder – here the entropy measures how the energy transferred is distributed among the parti- Epoxyethane cles of matter. See also Boltzmann formula. enzyme /en-zÿm/ A protein, with a rela- epoxy resin /i-poks-ee/ See epoxyethane. tive molecular mass between 105 and 107, that catalyzes a specific biochemical reac- Epsom salt /ep-sŏm/ See magnesium sul- tion. An enzyme mediates the conversion fate. of one substance (the substrate) to another (the product) by combining with the sub- equation See chemical equation. strate to form an intermediate complex. The enzyme molecule is very much larger equation of state An equation that inter- than the substrate molecule. Enzymes dif- relates the pressure, temperature, and vol- fer from inorganic catalysts in the follow- ume of a system, such as a gas. The ideal ing ways: gas equation (see gas laws) and the van der 1. they have a high degree of specificity – Waals equation are examples. enzymes can even distinguish between enantiomorphs; equilibrium /ee-kwă-lib-ree-ŭm, ek-wă-/ 2. an increase in temperature can cause a (pl. equilibriums or equilibria) In a re- decrease in the rate of reaction as a reversible chemical reaction: sult of the enzyme being denatured; A + B ˆ C + D 3. they are destroyed by too great a change The reactants are forming the products: in pH; A + B → C + D

103 equilibrium constant which also react to give the original reac- equivalent proportions, law of (law of tants: reciprocal proportions) When two chemi- C + D → A + B cal elements both form compounds with a The concentrations of A, B, C, and D third element, a compound of the first two change with time until a state is reached at elements contains them in the relative pro- which both reactions are taking place at portions they have in compounds with the the same rate. The concentrations (or pres- third element. For example, the mass ratio sures) of the components are then constant of carbon to hydrogen in methane (CH4) is – the system is said to be in a state of chem- 12:4; the ratio of oxygen to hydrogen in ical equilibrium. Note that the equilibrium water (H2O) is 16:2. In carbon monoxide (CO), the ratio of carbon to oxygen is is a dynamic one; the reactions still take 12:16. place but at equal rates. The relative proportions of the components determine the equivalent weight A measure of ‘com- ‘position’ of the equilibrium, which may be bining power’ formerly used in calcula- displaced by changing the conditions (e.g. tions for chemical reactions. The temperature or pressure). equivalent weight of an element is the number of grams that could combine with or equilibrium constant In a chemical equi- displace one gram of hydrogen (or 8 grams librium of the type of oxygen or 35.5 grams of chlorine). It is ˆ xA + yB zC + wD the relative atomic mass (atomic weight) The expression: divided by the valence. For a compound [A]x[B]y/[C]z[D]w the equivalent weight depends on the reac- where the square brackets indicate concen- tion considered. An acid, for instance, in trations, is a constant (Kc) when the system acid–base reactions has an equivalent is at equilibrium. Kc is the equilibrium con- weight equal to its molecular weight di- stant of the given reaction; its units depend vided by the number of acidic hydrogen on the stoichiometry of the reaction. For atoms. gas reactions, pressures are often used instead of concentration. The equilibrium erbium /er-bee-ŭm/ A soft malleable sil- n very element of the lanthanoid series of constant is then Kp, where Kp = Kc . Here n is the number of moles of product minus metals. It occurs in association with other the number of moles of reactant; for in- lanthanoids. Erbium has uses in the metal- stance, in lurgical and nuclear industries and in mak- 3H + N ˆ 2NH ing glass for absorbing infrared radiation. 2 2 3 ° ° n is 2 – (1 + 3) = –2. Symbol: Er; m.p. 1529 C; b.p. 2863 C; r.d. 9.066 (25°C); p.n. 68; r.a.m. 167.26. equipartition of energy /ee-kwă-par-tish- erg A former unit of energy used in the ŏn, ek-wă-/ The principle that the total en- c.g.s. system. It is equal to 10–7 joule. ergy of a molecule is, on average, equally distributed among the available DEGREES OF Erlenmeyer flask /er-lĕn-mÿ-er/ A coni- FREEDOM. It is only approximately true in cal glass laboratory flask with a narrow most cases. neck. It is named for the German chemist Richard August Carl Emil Erlenmeyer equivalence point The point in a titra- (1825–1909). tion at which the reactants have been added in equivalent proportions, so that ESR See electron spin resonance. there is no excess of either. It differs slightly from the end point, which is the essential amino acid See amino acid. observed point of complete reaction, because of the effect of the indicator, errors, essential oil Any pleasant-smelling etc. volatile oil obtained from various plants,

104 ethane-1,2-diol widely used in making flavorings and per- ethane /eth-ayn/ (C2H6) A gaseous alkane fumes. Most consist of terpenes and they obtained either from the gaseous fraction are obtained by steam distillation or sol- of crude oil or by the ‘cracking’ of heavier vent extraction. fractions. Ethane is the second member of the homologous series of alkanes. ester A type of organic compound formed by reaction between an acid and an alco- ethanedioic acid /eth-ayn-dÿ-oh-ik/ (ox- hol. If the acid is a carboxylic acid, the for- alic acid; (COOH)2) A white crystalline mula is RCOOR′, where R and R′ are organic acid that occurs naturally in organic groups. Esters of low-molecular rhubarb, sorrel, and other plants of the weight acids and alcohols are volatile fra- genus Oxalis. It is slightly soluble in water, grant compounds. Esters of some long- highly toxic, and used in dyeing and as a chain carboxylic acids occur naturally in chemical reagent. fats and oils. Esters can be prepared by direct reaction of acids and alcohols, with a ethane-1,2-diol (ethylene glycol; glycol; dehydrating agent to take out the water CH2(OH)CH2(OH)) A syrupy organic liq- and displace the equilibrium. Reaction of uid commonly used as antifreeze and as a alcohols with acyl halides also gives esters. starting material in the manufacture of See also carboxylic acid; saponification; Dacron. The compound is manufactured glyceride. from ethene by oxidation over suitable catalysts to form epoxyethane, with subse- esterification /es-te-ri-fă-kay-shŏn/ The quent hydrolysis to the diol. reaction of an acid with an alcohol to form CH an ester and water. The reaction is an equi- 3 librium of the form: ˆ CH3COOH + C2H5OH CH CH3COOC2H5 + H2O In the preparation of esters the ester is O O distilled off or the water is removed to increase the yield. The reverse reaction is hydrolysis. HC CH O CH ethanal /eth-ă-nal/ (acetaldehyde; CH3 3 CH3CHO) A water-soluble liquid alde- Ethanal trimer hyde used as a starting material in the manufacture of several other compounds. CH3 Ethanal can be prepared by the oxidation of ethanol. It is manufactured by the catalytic oxidation of ethyne with oxygen CH using copper(II) chloride and palladium(II) O chloride as catalysts. The mixture of gases O is bubbled through an aqueous solution of the catalysts; the reaction involves forma- H C 3 CH HC CH3 tion of an intermediate organometallic complex with Pd2+ ions. With dilute acids ethanal polymerizes to ethanal trimer O O (C3O3H3(CH3)3, formerly called paralde- CH hyde), which is a sleep-inducing drug. Below 0°C ethanal tetramer is formed (C4O4H4(CH3)4, formerly called metalde- CH hyde), which is used as a slug poison and a 3 fuel in small portable stoves. Ethanal tetramer

105 ethanoate ethanoate /eth-ă-noh-ayt/ (acetate; Ethene is the first member of the homolo- – CH3COO ) A salt or ester of ETHANOIC gous series of alkenes. ACID (acetic acid). ether /ee-th’er/ A type of organic com- ethanoic acid /eth-ă-noh-ik/ (acetic acid; pound containing the group –O–. Simple ′ CH3COOH) A colorless viscous liquid or- ethers have the formula R–O–R , where R ganic acid with a pungent odor (it is the and R′ are alkyl or aryl groups, which may acid in vinegar). Below 16.7°C it solidifies or may not be the same. They are either to a glassy solid (glacial ethanoic acid). It is gases or very volatile liquids and are very made by the oxidation of ethanol or bu- flammable. The commonest example is tane, or by the continued fermentation of ethoxyethane (diethylether, C2H5OC2H5) beer or wine. It is made into ethenyl used formerly as an anesthetic. Ethers now ethanoate (vinyl acetate) for making poly- find application as solvents. They are pre- mers. Cellulose ethanoate (acetate) is made pared in the laboratory by the dehydration from ethanoic anhydride. See cellulose ac- of alcohols with concentrated sulfuric acid. etate. An excess of alcohol is used to ensure that only one molecule of water is removed ethanol /eth-ă-nol, -nohl/ (ethyl alcohol; from each pair of alcohol molecules. They alcohol; C2H5OH) A colorless volatile liq- are generally unreactive, but the C–O bond uid alcohol. Ethanol occurs in intoxicating can be cleaved by reaction with HI or PCl5. drinks, in which it is produced by fermen-

tation of a sugar: . . . → . C6H12O6 2C2H5OH + 2CO2 O Yeast is used to cause the reaction. At about 15% alcohol concentration (by vol- R R’ ume) the reaction stops because the yeast is killed. Higher concentrations of alcohol Ether are produced by distillation. Apart from its use in drinks, alcohol is used as a solvent and to form ethanal. For- ethoxyethane /i-thoks-ee-eth-ayn/ (ether; merly, the main source was by fermenta- diethylether; C2H5OC2H5) A colorless tion of molasses, but now catalytic volatile liquid. Ether is well known for its hydration of ethene is used to manufacture characteristic smell and anesthetic proper- industrial ethanol. See also methylated ties, also for its extreme flammability. It spirits. still finds some application as an anesthetic when more modern materials are unsuit- ethanoyl chloride /eth-ă-noh-ăl/ (acetyl able; it is also an excellent solvent. Its man- chloride; CH3COCl) A liquid acyl chloride ufacture is an extension of the laboratory used as an acetylating agent. synthesis: ethanol vapor is passed into a mixture of excess ethanol and concen- ethanoyl group (acetyl group) The group trated sulfuric acid at 140°C: → RCO–. C2H5OH + H2SO4 C2H5.O.SO2.OH + H2O → ethene /eth-een/ (ethylene; C2H4) A C2H5O.SO2.OH + C2H5OH gaseous alkene. Ethene is not normally pre- C2H5OC2H5 + H2SO4 sent in the gaseous fraction of crude oil but can be obtained from heavier fractions by ethyl acetate /eth-ăl/ See ethyl ethanoate. catalytic cracking. This is the principal industrial source. The compound is impor- ethyl alcohol See ethanol. tant as a starting material in the organic-chemicals industry (e.g. in the ethylamine /eth-ă-lă-meen, -lam-een/ manufacture of ethanol) and as the starting (aminoethane; C2H5NH2) A colorless liq- material for the production of polyethene. uid amine. It can be prepared from

106 exa- chloroethane heated with concentrated duction of other vinyl compounds. Until aqueous ammonia: recently, ethyne was manufactured by the → C2H5Cl + NH3 C2H5NH2 + HCl synthesis and subsequent hydrolysis of cal- It is used in manufacturing certain dyes. cium dicarbide, a very expensive procedure. Modern methods increasingly ethyl bromide See bromoethane. employ the cracking of alkanes. ethyl carbamate See urethane. ethynide /eth-ă-nÿd, -nid/ See carbide. ethyl chloride See chloroethane. eudiometer /yoo-dee-om-ĕ-ter/ An apparatus for the volumetric analysis of gases. ethyl dibromide /dÿ-broh-mÿd/ See dibromoethane. europium /yû-roh-pee-ŭm/ A silvery element of the lanthanoid series of metals. It ethylene /eth-ă-leen/ See ethene. occurs in association with other lanthanoids. Its main use is in a mixture of eu- ethylenediamine /eth-ă-leen-dÿ-ă-meen/ ropium and yttrium oxides widely An organic compound, H2NCH2CH2NH2. employed as the red phosphor in television It is important in inorganic chemistry be- screens. The metal is used in some super- cause it may function as a bidentantate lig- conducting alloys. and, coordinating to a metal ion by the Symbol: Eu; m.p. 822°C; b.p. 1597°C; lone pairs on the two nitrogen atoms. In r.d. 5.23 (25°C); p.n. 63; r.a.m. 151.965. the names of complexes it is given the ab- breviation en. eutectic /yoo-tek-tik/ A mixture of two substances in such proportions that no ethylenediamine tetraacetic acid /eth-ă- other mixture of the same substances has a leen-dÿ-ă-meen tet-ră-see-tik/ See edta. lower freezing point. If a solution containing the proportions of the eutectic is cooled ethylene glycol See ethane-1,2-diol. no solid is deposited until the freezing point of the eutectic is reached, when two ethylene oxide See epoxyethane. solid phases are simultaneously deposited in the same proportions as the mixture; ethylene tetrachloride /tet-ră-klor-ÿd, these two solid phases form the eutectic. If -id, -kloh-rÿd, -rid/ See tetrachloroethane. one of the substances is water the eutectic can also be referred to as a cryohydrate. ethyl ethanoate (ethyl acetate; C2H5OOCCH3) An ester formed from evaporation 1. A change of state from ethanol and ethanoic acid. It is a fragrant liquid to gas (or vapor). Evaporation can liquid used as a solvent for plastics and in take place at any temperature, the rate in- flavoring and perfumery. creasing with temperature. Some molecules in the liquid have enough energy to escape ethyl iodide See iodoethane. into the gas phase (if they are near the surface and moving in the right direction). Be- ethyne /eth-ÿn/ (acetylene; C2H2) A cause these are the molecules with higher gaseous alkyne. Traditionally ethyne has kinetic energies, evaporation results in a found use in oxy-acetylene welding cooling of the liquid. torches, since its combustion with oxygen 2. A change from solid to vapor, especially produces a flame of very high temperature. occurring at high temperatures close to the It is also important in the organic chemi- melting point of the solid. Thin films of cals industry for the production of metal can be evaporated onto a surface in chloroethene (vinyl chloride), which is the this way. starting material for the production of polyvinyl chloride (PVC), and for the pro- exa- Symbol: E A prefix denoting 1018.

107 excitation excitation /eks-ÿ-tay-shŏn/ The process explosive A substance or mixture which of producing an excited state of an atom, can rapidly decompose upon detonation molecule, etc. producing large amounts of heat and gases. The three most important classes of explo- excitation energy The energy required to sives are: change an atom, molecule, etc. from one 1. Propellants which burn steadily, and are quantum state to a state with a higher en- used as rocket fuels. ergy. The excitation energy (sometimes 2. Initiators which are very sensitive and called excitation potential) is the difference are used in small amounts to detonate between two energy levels of the system. less sensitive explosives. 3. High explosives which need an initiator, excited state A state of an atom, mol- but are very powerful. ecule, or other system, with an energy greater than that of the ground state. Com- E–Z convention A convention for the de- pare ground state. scription of a molecule showing cis–trans exclusion principle The principle, enun- isomerism. In a molecule ABC=CDE, ciated by Pauli in 1925, that no two elec- where A, B, D, and E are different groups, trons in an atom can have an identical set a sequence rule (see CIP system) is applied of quantum numbers. to the pair A and B to find which has priority and similarly to the pair C and D. If exothermic /eks-oh-th’er-mik/ Denoting the two groups of higher priority are on the a chemical reaction in which heat is same side of the bond then the isomer is evolved (i.e. heat flows from the system or designated Z (from German zusammen, to- the temperature rises). Combustion is an gether). If they are on opposite sides the example of an exothermic process. Com- isomer is designated E (German entgegen, pare endothermic. opposite).

108 F

face-centered cubic crystal (f.c.c.) A anion (originally rules 1 and 2). Fajan’s crystal structure in which the unit cell has third rule states that covalent character is atoms, ions, or molecules at each corner greater for cations with a non-rare gas con- and at the center of each face of a cube figuration than for those with a complete (also called cubic close-packed). It has a co- octet, charge and size being approximately ordination number of 12. The structure is equal. For example, Cu+ is more polarizing close-packed and made up of layers of than Na+ (approximately the same size) be- atoms in which each atom is surrounded by cause the d-electrons around Cu+ do not six others arranged hexagonally. Copper shield the nucleus as effectively as the com- and aluminum have face-centered cubic plete octet in Na+. The rules are named for structures. The layers are packed one on the Polish–American physical chemist top of the other, with the second layer fit- Kasimir Fajans (1887–1975). ting into the holes of the first layer. The third layer is in a different set of holes farad /fa-răd, -rad/ Symbol: F The SI unit formed by the second layer. If the layers are of capacitance. When the plates of a capac- designated A, B, C, the packing is arranged itor are charged by one coulomb and there ABCABC is a potential difference of one volt between in contrast to hexagonal close packing, in them, then the capacitor has a capacitance which the layers are arranged of one farad. One farad = 1 coulomb volt–1 ABABAB. (CV–1). The unit is named for the British physicist and chemist Michael Faraday Fahrenheit scale A TEMPERATURE SCALE (1791–1867). in which the ice temperature is taken as 32° and the steam temperature is taken as 212° faraday /fa-ră-day/ Symbol: F A unit of (both at standard pressure). The scale is electric charge equal to the charge required not used for scientific purposes. To convert to discharge one mole of a singly-charged between degrees Fahrenheit (F) and de- ion. One faraday is 9.648 670 × 104 grees Celsius (C) the formula coulombs. See Faraday’s laws. C/5 = (F – 32)/9 is used. The scale is named for the German Faraday constant See Faraday’s laws. physicist Daniel Fahrenheit (1686–1736). Faraday’s laws (of electrolysis) Two laws Fajan’s rules /faj-ănz/ Rules that deal resulting from the work of Michael Fara- with variations in the degree of covalent day on electrolysis: character in ionic compounds in terms of 1. The amount of chemical change pro- polarization effects. Decrease in size and duced is proportional to the electric increase in charge for cations is regarded as charge passed. making them more polarizing and for an- 2. The amount of chemical change pro- ions an increase in both charge and size duced by a given charge depends on the makes them more polarizable. Thus cova- ion concerned. lent character is said to increase with in- More strictly it is proportional to the rela- creasing polarizing power of the cation tive ionic mass of the ion, and the charge and/or increasing polarizability of the on it. Thus the charge Q needed to deposit

109 fat m grams of an ion of relative ionic mass, that take place on timescales of about a M, carrying a charge Z is given by: femtosecond (10–15s). Femtochemistry be- Q = FmZ/M came possible with the construction of F, the Faraday constant, has a value of one lasers that could be pulsed in femtosec- faraday, i.e. 9.648 670 × 104 coulombs. onds. Femtochemistry can be regarded as very high speed ‘photography’ of chemical fat See glyceride. reactions. Typically, a short pulse of radiation can initiate a change, with subsequent fatty acid See carboxylic acid. pulses at short intervals used to investigate the intermediates spectroscopically. The f-block elements The block of elements technique has enabled entities that exist in the periodic table that have two outer s- only for a short time, such as activated electrons and an incomplete penultimate complexes, to be studied. The detailed subshell of f-electrons. The f-block consists mechanisms of many chemical reactions of the lanthanoids (cerium to lutetium) and have been investigated in this way. the actinoids (thorium to lawrencium). fermentation A chemical reaction pro- f.c.c. See face-centered cubic crystal. duced by microorganisms (molds, bacteria, or yeasts). A common example is the for- fay-lingz Fehling’s solution / / A solution mation of ethanol from sugars: used to test for the aldehyde group C H O → 2C H OH + 2CO (–CHO). It is a freshly made mixture of 6 12 6 2 5 2 copper(II) sulfate solution with alkaline fermi /fer-mee/ A unit of length equal to potassium sodium 2,3-dihydroxybutane- 10–15 meter. It was formerly used in atomic dioate (tartrate). The aldehyde, when and nuclear physics. The unit is named for heated with the mixture, is oxidized to a the Italian–American physicist Enrico carboxylic acid, and a red precipitate of Fermi (1901–54). copper(I) oxide and copper metal is produced. The tartrate is present to complex fer-mee-ŭm with the original copper(II) ions to prevent fermium / / A radioactive precipitation of copper(II) hydroxide. The transuranic element of the actinoid series, solution is named for the German organic not found naturally on Earth. It is pro- chemist Hermann Christian von Fehling duced in very small quantities by bom- 239 253 (1812–85). barding Pu with neutrons to give Fm (half-life 3 days). Several other short-lived feldspar (felspar) A member of a large isotopes have been synthesized. group of abundant crystalline igneous Symbol: Fm; p.n. 100; most stable iso- 257 rocks, mainly silicates of aluminum with tope Fm (half-life 100.5 days). calcium, potassium, and sodium. The alkali feldspars have mainly potassium with ferric chloride /fe-rik/ See iron(III) chlo- a little sodium and no calcium; the plagio- ride. clase feldspars vary from sodium-only to calcium-only, with little or no potassium. ferric oxide See iron(III) oxide. Feldspars are used in making ceramics, enamels, and glazes. ferric sulfate See iron(III) sulfate. femto- Symbol: f A prefix denoting 10–15. ferricyanide See cyanoferrate. For example, 1 femtometer (fm) = 10–15 meter (m). ferrite /fe-rÿt/ A nonconducting magnetic ceramic material, general formula MO. femtochemistry /fem-toh-kem-iss-tree/ Fe2O4 (where M is a divalent transition The study of atomic and molecular metal such as cobalt, nickel, or zinc). Fer- processes, particularly chemical reactions, rites are used to make powerful magnets in

110 fine structure high-frequency electronic devices such as and dn/dt is the amount of solute crossing radar sets. the area A per unit time. D is constant for a specific solute and solvent at a specific ferrocene /fe-roh-seen/ (Fe(C5H5)2) An temperature. Fick’s law was formulated by orange crystalline solid. It is an example of the German physiologist Adolf Eugen Fick a sandwich compound, in which an iron(II) (1829–1901) in 1855. ion is coordinated to two cyclopentadienyl ions. The bonding involves overlap of d or- filler A solid material used to modify the bitals on the iron with the pi electrons in physical properties or reduce the cost of the cyclopentadienyl ring. The compound synthetic compounds, such as rubbers, melts at 173°C, is soluble in organic sol- plastics, paints, and resins. Slate powder, vents, and can undergo substitution reac- glass fiber, mica, and cotton are all used as tions on the rings. It can be oxidized to the fillers. + blue cation (C5H5)2Fe . The systematic π name is di- -cyclopentadienyl iron(II). filter See filtration. ferrocyanide /fe-roh-sÿ-ă-nÿd/ See cyano- filter pump A type of vacuum pump in ferrate. which a jet of water forced through a nozzle carries air molecules out of the system. ferromagnetism /fe-roh-mag-nĕ-tiz-ăm/ Filter pumps cannot produce pressures See magnetism. below the vapor pressure of water. They are used in the laboratory for vacuum fil- /fe-ros-oh-fe-rik/ See ferrosoferric oxide tration, distillation, and similar techniques triiron tetroxide. requiring a low-grade vacuum. ferrous chloride /fe-rŭs/ See iron(II) chlo- filtrate See filtration. ride. filtration The process of removing sus- ferrous oxide See iron(II) oxide. pended particles from a fluid by passing or forcing the fluid through a porous material ferrous sulfate See iron(II) sulfate. (the filter). The fluid that passes through fertilizer A substance added to soil to in- the filter is the filtrate. In laboratory filtra- crease its fertility. Artificial fertilizers gen- tion, filter paper or sintered glass is com- erally consist of a mixture of chemicals monly used. designed to supply nitrogen (N), as well as some phosphorus (P) and potassium (K), fine organic chemicals Carbon com- known as PKN fertilizers. Typical chemi- pounds, such as pesticides, dyes, and cals include ammonium nitrate, ammo- drugs, produced only in small quantities. nium phosphate, ammonium sulfate, and Their main requirement is that they must potassium carbonate. have a high degree of purity, often higher than 95%. They are manufactured for spe- Fick’s law /fiks/ A law describing the dif- cial purposes, e.g. for use in spectroscopy, fusion that occurs when solutions of differ- pharmacology, and electronics. ent concentrations come into contact, with molecules moving from regions of higher fine structure Closely spaced lines seen at concentration to regions of lower concen- high resolution in a spectral line or band. tration. Fick’s law states that the rate of Fine structure may be caused by vibration diffusion dn/dt, called the diffusive flux of the molecules or by electron spin. Hy- and denoted J, across an area A is given by: perfine structure, seen at very high resolu- dn/dt = J = –DA∂c/∂x, where D is a con- tion, is caused by the atomic nucleus stant called the diffusion constant, ∂c/∂x is affecting the possible energy levels of the the concentration gradient of the solute, atom.

111 fireclay fireclay A refractory clay containing high an easily available source of motor fuel. proportions of alumina (aluminum oxide) The process is named for the German and silica (silicon(IV) oxide), used for mak- chemists Franz Fischer (1877–1948) and ing firebricks and furnace linings. Hans Tropsch (1889–1935). firedamp Methane occurring in coal Fittig reaction See Wurtz reaction. mines. Explosions can occur if quantities of methane accumulate. The air left after fixation of nitrogen See nitrogen fixa- an explosion is called blackdamp. After- tion. damp is the poisonous carbon monoxide formed. fixing, photographic A stage in the development of exposed photographic film first-order reaction A reaction in which or paper in which unexposed silver halides the rate of reaction is proportional to the in the emulsion are dissolved away. The concentration of one of the reacting sub- fixing bath contains a solution of ammo- stances. The concentration of the reacting nium or sodium thiosulfate(IV), and is em- substance is raised to the power one; i.e. ployed after the initial development rate = k[A]. For example, the decomposi- (chemical reduction) of the latent silver tion of hydrogen peroxide is a first-order image. reaction, rate = k[H2O2] flame-ionization detector See gas chro- Similarly the rate of decay of radioactive matography. material is a first-order reaction, rate = k[radioactive material] flame test A preliminary test in qualita- For a first-order reaction, the time for a tive analysis in which a small sample of a definite fraction of the reactant to be con- chemical is introduced into a nonluminous sumed is independent of the original con- Bunsen-burner flame on a clean platinum centration. The units of k, the rate wire. The flame vaporizes part of the sam- constant, are s–1. ple and excites some of the atoms, which emit light at wavelengths characteristic of Fischer projection /fish-er/ A way of rep- the metallic elements in the sample. Thus resenting the three-dimensional structure the observation of certain colors in the of a molecule in two dimensions. The mol- flame indicates the presence of these ele- ecule is drawn using vertical and horizon- ments. The same principles are applied in tal lines. Horizontal lines represent bonds the modern instrumental method of spec- that come out of the paper. Vertical lines trographic analysis. represent bonds that go into the paper (or are in the plane of the paper). Named for Emil Fischer, the convention was formerly FLAME TEST COLORS used for representing the absolute configu- Element Flame color ration of sugars. barium green calcium brick red Fischer–Tropsch process /fish-er tropsh/ lithium crimson The catalytic hydrogenation of carbon potassium pale lilac monoxide in the ratio of 2:1 hydrogen to sodium yellow carbon monoxide at 200°C to produce hy- strontium red drocarbons, especially motor fuel. The carbon monoxide is derived from water gas, which uses coal or natural gas as a source flare stack A chimney at the top of which of carbon, and the catalyst is finely divided unwanted gases are burnt in an oil refinery nickel. The process was extensively used in or other chemical plant. Germany during World War II and is still used in countries in which crude oil is not flash photolysis A technique for investi-

112 fluorine gating free radicals in gases. The gas is held fluoridation /floo-ŏ-ră-day-shŏn/ The in- at low pressure in a long glass or quartz troduction of small quantities of fluoride tube, and an absorption spectrum taken compounds into the water supply as a pub- using a beam of light passing down the lic-health measure to reduce the incidence tube. The gas can be subjected to a very of tooth decay in children. brief intense flash of light from a lamp outside the tube, producing free radicals, fluoride /floo-ŏ-rÿd, -rid/ See halide. which are identified by their spectra. Mea- surements of the intensity of spectral lines fluorination /floo-ŏ-ră-nay-shŏn/ See halogenation. can be made with time using an oscillo- scope, and the kinetics of very fast reac- fluorine /floo-ŏ-reen, -rin/ A slightly tions can thus be investigated. greenish-yellow highly reactive gaseous element belonging to the halogens (group 17 The lowest temperature at flash point of the periodic table, formerly VIIA). It oc- which sufficient vapor is given off by a curs notably as fluorite (CaF2) and cryolite flammable liquid to ignite in the presence (Na3AlF3) but traces are also widely dis- of a spark. tributed with other minerals. It is slightly more abundant than chlorine, accounting flocculation /flok-yŭ-lay-shŏn/ (coagula- for about 0.065% of the Earth’s crust. The tion) The combining of the particles of a high reactivity of the element delayed its finely divided precipitate, such as a colloid, isolation. Fluorine is now prepared by elec- into larger particles or clumps that sink trolysis of molten KF/HF electrolytes, and are easier to filter off. using copper or steel apparatus. Its preparation by chemical methods is impossible. flocculent /flok-yŭ-lănt/ Describing a pre- Fluorine compounds are used in the cipitate that has aggregated in wooly steel industry, glass and enamels, uranium masses. processing, aluminum production, and in a range of fine organic chemicals. Fluorine is flotation See froth flotation. the most reactive and most electronegative element known; in fact it reacts directly fluid A state of matter that is not a solid – with almost all the elements, including the that is, a liquid or a gas. All fluids can flow, rare gas xenon. As the most powerful oxi- and the resistance to flow is the viscosity. dizing agent known, it has the pronounced characteristic of bringing out the higher fluidization /floo-id-ă-zay-shŏn/ The sus- oxidation states when combined with pension of a finely-divided solid in an up- other elements. Ionic fluorides contain the – ion, which is very similar to the ward-flowing liquid or gas. This small F O2– ion. With the more electronegative ele- suspension mimics many properties of liq- ments, fluorine forms an extensive range of uids, such as allowing objects to ‘float’ in compounds, e.g. SF , NF , and PF , in it. Fluidized beds so constructed are impor- 6 3 5 which the bonding is essentially covalent. tant industrially. A vast number of organic compounds are known in which hydrogen may be replaced fluorescein /floo-ŏ-ress-ee-in/ A fluores- by fluorine and in which the C–F bond is cent dye used as an absorption indicator. characteristically very stable. Examples are CF2=CF2, C6H4F2, and CF3COOH; the fluorescence /floo-ŏ-ress-ĕns/ The ab- bonding is again essentially covalent. sorption of energy by atoms, molecules, Fluorine reacts explosively with hydro- etc., followed by immediate emission of gen, even in the dark, to form hydrogen electromagnetic radiation as the particles fluoride, HF, which polymerizes as a result make transitions to lower energy states. of hydrogen bonding and has a boiling Compare phosphorescence. point very much higher than that of HCl

113 fluorite

(HF b.p. 19°C; HCl b.p. –85°C). Unlike fluxional molecule A molecule in which the other halogens, fluorine does not form the constituent atoms change their relative higher oxides or oxyacids; oxygen difluo- positions so quickly at room temperature ride in fact reacts with water to give hy- that the normal concept of structure is in- drogen fluoride. adequate; i.e. no specific structure exists Fluorine is strongly electronegative and for longer than about 10–2 second and the exhibits a strong electron withdrawing ef- relative positions become indistinguish- ° fect on adjacent bonds, thus CF3COOH is able. For example ClF3 at –60 C has a dis- a strong acid (whereas CH3COOH is not). tinct ‘T’ shape but at room temperature the Although the coordination number seldom fluorine atoms are visualized as moving exceeds one there are cases in which fluo- rapidly over the surface of the chlorine atom in a state of exchange and are effec- rine bridging occurs, e.g. (SbF5)n. The element is sufficiently reactive to combine tively identical. directly with the rare gas xenon at 400°C ° foam A dispersion of bubbles of gas in a to form XeF2 and XeF4. At 600 C and high liquid, usually stabilized by a SURFACTANT. pressure it will even form XeF6. Fluorine and hydrogen fluoride are ex- Solid foams, such as expanded polystyrene tremely dangerous and should only be used or foam rubber, are made by allowing liq- in purpose-built apparatus; gloves and face uid foams to set. shields should be used when working with /for-mal-dĕ-hÿd/ See hydrofluoric acid and accidental exposure formaldehyde methanal. should be treated as a hospital emergency. Symbol: F; b.p. –188.14°C; m.p. formalin /for-mă-lin/ See methanal. –219.62°C; d. 1.696 kg m–3 (0°C); p.n. 9; r.a.m. 18.99840.32. formate /for-mayt/ See methanoate. fluorite /floo-ŏ-rÿt/ (fluorspar) A mineral formic acid /for-mik/ See methanoic acid. form of calcium fluoride (CaF2), used in making some cements and types of glass. formula (pl. formulas or formulae) A rep- See also calcium-fluoride structure. resentation of a chemical compound using symbols for the atoms and subscript num- fluorite structure See calcium-fluoride bers to show the numbers of atoms present. structure. See empirical formula; general formula; molecular formula; structural formula. fluorocarbon /floo-ŏ-rŏ-kar-bŏn/ A compound derived from a hydrocarbon by re- formyl group /for-măl/ The group placing hydrogen atoms with fluorine HCO–. atoms. Fluorocarbons are unreactive and most are stable up to high temperatures. fossil fuel A mineral fuel that forms un- They have a variety of uses – in aerosol derground from the remains of living or- propellants, oils and greases, and synthetic ganisms. Fossil fuels include coal, natural polymers such as PTFE. See also chloroflu- gas, peat, and petroleum. orocarbon. fraction A mixture of liquids with similar fluorspar /floo-er-spar/ See fluorite. boiling points collected by fractional distillation. flux 1. A substance used to keep metal surfaces free of oxide in soldering. See sol- fractional crystallization Crystalliza- der. tion of one component from a mixture in 2. A substance used in smelting metals to solution. When two or more substances are react with silicates and other impurities present in a liquid (or in solution), on cool- and form a low-melting slag. ing to a lower temperature one substance

114 Friedel–Crafts reaction will preferentially form crystals, leaving cals are produced by breaking a covalent the other substance in the liquid (or dis- bond; for example: → solved) state. Fractional crystallization can CH3Cl CH3• + Cl• thus be used to purify or separate sub- They are often formed in light-induced stances if the correct conditions are reactions. Free radicals are extremely reac- known. tive and can be stabilized and isolated only under special conditions. fractional distillation (fractionation) A distillation carried out with partial reflux, free-radical substitution See substitu- using a long vertical column (fractionating tion reaction. column). It utilizes the fact that the vapor phase above a liquid mixture is generally freezing The process by which a liquid is richer in the more volatile component. If converted into a solid by cooling; the re- the region in which refluxing occurs is suf- verse of melting. ficiently long, fractionation permits the complete separation of two or more freezing mixtures Two or more sub- volatile liquids. Fractionation is the funda- stances mixed together to produce a low mental process for producing petroleum temperature. A mixture of sodium chloride from crude oil. and ice in water (–20°C) is a common ex- Unlike normal reflux, the fractionating ample. column may be insulated to reduce heat loss, and special designs are used to maxi- freezing point The temperature at which mize the liquid-vapour interface. a liquid is in equilibrium with its solid phase at standard pressure and below fractionation /frak-shŏ-nay-shŏn/ See which the liquid freezes or solidifies. This fractional distillation. temperature is always the same for a particular liquid and is numerically equal to francium /fran-see-ŭm/ A radioactive ele- the melting point of the solid. ment of the alkali-metal group. It is found on Earth only as a short-lived product of See depression radioactive decay, occurring in uranium freezing point constant ores in minute quantities. A large number of freezing point. of radioisotopes of francium are known. Symbol: Fr; m.p. 27°C; b.p. 677°C; p.n. French chalk See talc. 87; most stable isotope 223Fr (half-life 21.8 minutes). Frenkel defect /frenk-ĕl/ See defect.

Frasch process /frash/ See sulfur. Freons /free-onz/ (Trademark) Various chlorofluorocarbons (CFCs) and fluoro- free electron An electron that can move carbons used as refrigerants. See chloroflu- from one atom or molecule to another orocarbon; fluorocarbon. under the influence of an applied electric field. Movement of free electrons in a con- Friedel–Crafts reaction /free-dĕl kraft/ ductor constitutes an electric current. Free A method for the substitution of an alkyl electrons are also involved in metallic or acyl group onto a benzene ring. The aro- bonds (see metals). matic hydrocarbon (e.g. benzene) is refluxed with a haloalkane or acyl halide free energy A measure of the ability of a using aluminum chloride catalyst. The system to do useful work. See Gibbs func- product is an alkylarene, e.g.: → tion; Helmholtz function. C6H6 + CH3I C6H5CH3 + HI or a ketone, for example: → free radical An atom or group of atoms C6H6 + CH3COCl C6H5COCH3 + with a single unpaired electron. Free radi- HCl

115 frontier orbital

CH3

+ CH3CI

benzene chloromethane methylbenzene (toluene)

Friedel–Crafts methylation O

C CH3 + CH3COCI

benzene ethanoyl chloride phenyl methyl ketone

Friedel-Crafts acetylation

Friedel–Crafts reactions

The aluminum chloride accepts a lone ated and particles of one constituent are pair of electrons on the chlorine, polarizing carried to the surface by bubbles of air, the chloroalkane to produce positive which adhere preferentially to one of the charge on the carbon. Electrophilic substi- constituents. Various additives are also tution then occurs. The reaction is named used to modify the surface properties of the for the French chemist Charles Friedel particles (e.g. to increase the adherence of (1832–99) and the American chemist air bubbles). James Crafts (1839–1917). fructose /fruk-tohs, frûk-/ (fruit sugar; frontier orbital Either of two orbitals in C6H12O6) A sugar found in fruit juices, a molecule: the highest occupied molecular honey, and cane sugar. It is a ketohexose, orbital (the HOMO) or the lowest unoccu- existing in a pyranose form when free. In pied molecular orbital (the LUMO). The combination (e.g. in sucrose) it exists in the HOMO is the orbital with the highest en- furanose form. ergy level occupied at absolute zero temperature. The LUMO is the lowest-energy fruit sugar See fructose. unoccupied orbital at absolute zero. For a particular molecule the nature of these two fuel cell A type of cell in which fuel is con- orbitals is very important in determining verted directly into electricity. In one form, the chemical properties. Frontier-orbital theory, which considers the symmetry of hydrogen gas and oxygen gas are fed to the these orbitals, has been very successful in surfaces of two porous nickel electrodes explaining such reactions as the immersed in potassium hydroxide solu- DIELS–ALDER REACTION. See also Wood- tion. The oxygen reacts to form hydroxyl – ward–Hoffmann rules. (OH ) ions, which it releases into the solution, leaving a positive charge on the elec- froth flotation An industrial technique trode. The hydrogen reacts with the OH– for separating the required parts of ores ions in the solution to form water, giving from unwanted gangue. The mineral is pul- up electrons to leave a negative charge on verized and mixed with water, to which a the other electrode. Large fuel cells can frothing agent is added. The mixture is aer- generate tens of amperes. Usually the e.m.f.

116 fusion is about 0.9 volt and the efficiency around mass, and time that form the basis of most 60%. systems of units. In SI, the fundamental units are the meter, the kilogram, and the fullerene /fûl-ĕ-reen/ See buckminster- second. See also base unit. fullerene. furan /fyoo-ran, fyoo-ran/ (furfuran; /fûl-ĕ-rÿt/ See buckminster- fullerite C4H4O) A heterocyclic liquid organic fullerene. compound. Its five-membered ring contains four carbon atoms and one oxygen fuller’s earth A natural clay used as an atom. The structure is characteristic of absorbent and industrial catalyst. some monosaccharide sugars (furanoses). fumaric acid /fyoo-ma-rik/ See butene- furanose /fyoo-ră-nohs/ A SUGAR that has dioic acid. a five-membered ring (four carbon atoms and one oxygen atom). fuming sulfuric acid See oleum. furfuran /fer-fŭ-răn, fer-fŭ-ran/ See furan. functional group A group of atoms in a compound that is responsible for the char- Describing a solid that has been acteristic reactions of the type of com- fused pound. Examples are: melted and solidified into a single mass. alcohol –OH Fused silica, for example, is produced by aldehyde –CHO melting sand. amine –NH2 ketone =CO. fused ring See ring. carboxylic acid –CO.OH acyl halide –CO.X (X = halogen) fusel oil /fyoo-zĕl, -sĕl/ A mixture of high- molecular-weight alcohols together with nitro compound –NO2 sulfonic acid –SO2.OH some esters and fatty acids, formed from nitrile –CN alcoholic fermentation and obtained dur- + diazonium salt –N2 ing distillation. It is used as a source of diazo compound –N=N– higher alcohols. fundamental units The units of length, fusion Another word for melting.

117 G

gadolinium /gad-ŏ-lin-ee-ŭm/ A ductile nuclei of atoms. Gamma waves have very malleable silvery element of the lanthanoid high frequency (short wavelength). series of metals. It occurs in association Gamma radiation shows particle proper- with other lanthanoids. Gadolinium is ties much more often than wave properties. used in alloys, magnets, and in the elec- The energy of a gamma photon, given by tronics industry. W = hv Symbol: Gd; m.p. 1313°C; b.p. (where h is the Planck constant), can be 3266°C; r.d. 7.9 (25°C); p.n. 64; r.a.m. very high. A gamma photon of 1024 Hz has 157.25. an energy of 6.6 × 10–10 J. See also electromagnetic radiation. galactose /gă-lak-tohs/ (C6H12O6) A SUGAR found in lactose and many polysac- gamma rays Streams of gamma radia- charides. It is an aldohexose, isomeric with tion. glucose. gangue /gang/ The rock or other undesir- galena /gă-lee-nă/ (lead glance) A mineral able material occurring in an ore. form of lead(II) sulfide. It is the principal ore of lead. gas The state of matter in which forces of attraction between the particles of a sub- gallium /gal-ee-ŭm/ A soft silvery low- stance are small. The particles have free- melting metallic element belonging to dom of movement and gases, therefore, group 3 (formerly IIIA) of the periodic have no fixed shape or volume. The atoms table. It is found in minute quantities in and molecules of a gas are in a continual several ores, including zinc blende (ZnS) state of motion and are continually collid- and bauxite (Al2O3.H2O). Gallium is used ing with each other and with the walls of in low-melting alloys, high-temperature the containing vessel. These collisions with thermometers, and as a doping impurity in the walls create the pressure of a gas. semiconductors. Gallium arsenide is a semiconductor used in light-emitting gas chromatography A technique widely diodes and in microwave apparatus. used for the separation and analysis of Symbol: Ga; m.p. 29.78°C; b.p. mixtures. Gas chromatography employs a 2403°C; r.d. 5.907 (solid at 20°C), 6.114 column packed with either a solid station- (liquid); p.n. 31; r.a.m. 69.723. ary phase (gas-solid chromatography or GSC) or a solid coated with a non-volatile galvanic cell /gal-van-ik/ See cell. liquid (gas-liquid chromatography or GLC). The whole column is placed in a galvanizing /gal-vă-nÿ-zing/ A process for thermostatically controlled heating jacket. coating steel with zinc by dipping in a bath A volatile sample is introduced into the col- of molten zinc, or by electrodeposition. umn using a syringe, and an unreactive car- The zinc protects the steel from corrosion. rier gas, such as nitrogen, passed through it. The components of the sample will be gamma radiation A form of electromag- carried along in this mobile phase. How- netic radiation emitted by changes in the ever, some of the components will cling

118 Gatterman–Koch reaction more readily to the stationary phase than Boyle’s and Charles’ laws can be com- others, either because they become at- bined into an equation of state for ideal tached to the solid surface or because they gases: dissolve in the liquid. The time taken for pVm = RT different components to pass through the where Vm is the molar volume and R the column is characteristic and can be used to molar gas constant. For n moles of gas identify them. The emergent sample is pV = nRT passed through a detector, which registers All real gases deviate to some extent the presence of the different components in from the gas laws, which are applicable the carrier gas. only to idealized systems of particles of Two types of detector are in common negligible volume with no intermolecular use: the katharometer, which measures forces. There are several modified equa- changes in thermal conductivity, and the tions of state that give a better description flame-ionization detector, which turns the of the behavior of real gases, the best volatile components into ions and registers known being the van der Waals equation. the change in electrical conductivity. gas–liquid chromatography See gas gas constant (universal gas constant) chromatography. Symbol: R The universal constant 8.314 34 J mol–1 K–1 appearing in the gasohol /gas-ŏ-hôl/ Alcohol (ethanol) ob- equation of state for an ideal gas. See gas tained by the industrial fermentation of laws. sugar for use as a motor fuel. It has been produced on a large scale in some countries. gaseous diffusion separation A technique for the separation of gases that relies gas oil One of the main fractions obtained on their slightly different atomic masses. from PETROLEUM by distillation, used as a For example, the isotopes of uranium (235U fuel for diesel engines. See diesel fuel. and 238U) can be separated by first preparing gaseous uranium hexafluoride from gasoline /gas-ŏ-leen, gas-ŏ-leen/ See petro- uranium ore. If this is then made to pass leum. through a series of fine pores, the molecules containing the lighter isotope of ura- gas-solid chromatography See gas chro- nium will pass through more quickly. As matography. the gases pass through successive ‘di- aphragms’, the proportion of lighter mol- Gatterman–Koch reaction A reaction ecules increases and a separation of over for substituting a formyl (methanoyl) 99% is attainable. This method has also group (HCO–) onto a benzene ring of an been applied to the separation of the iso- aromatic hydrocarbon. It is used in the in- topes of hydrogen. dustrial production of benzaldehyde from benzene: gas equation See gas laws. → C6H6 C6H5CHO The aromatic hydrocarbon is mixed with a gas laws Laws relating the temperature, Lewis acid, such as aluminum chloride, pressure, and volume of a fixed mass of and a mixture of carbon monoxide and the gas. The main gas laws are Boyle’s law and hydrogen chloride is passed through. The Charles’ law. The laws are not obeyed ex- first stage is the production of an H–C≡O+ actly by any real gas, but many common ion: → + – gases obey them under certain conditions, HCl + CO + AlCl3 HCO + AlCl4 particularly at high temperatures and low Copper (I) chloride (CuCl) is also added as pressures. A gas that would obey the laws a catalyst. The HCO+ ion acts as an elec- over all pressures and temperatures is a trophile in electrophilic substitution on the perfect or ideal gas. benzene ring.

119 Gatterman reaction

A variation of the reaction in which the particles enclose the whole dispersing HCO– group is substituted onto the ben- medium. Gels may be further subdivided zene ring of a phenol uses hydrogen into elastic gels (e.g. gelatin) and rigid gels cyanide rather than carbon monoxide. (e.g. silica gel). Typically, a mixture of zinc cyanide and hydrochloric acid is used, to give zinc chlo- gelatin /jel-ă-tin/ (gelatine) A pale yellow ride (which acts as a Lewis acid) and hy- protein obtained from the bones, hides, drogen cyanide. The electrophile in this and skins of animals, which forms a col- case is protonated hydrogen cyanide: loidal jelly when dissolved in hot water. It → + HCN + HCl + ZnCl2 HCNH + is used in jellies and other foods, to make – ZnCl3 capsules for various medicinal drugs, as an The phenol is first substituted to give an adhesive and sizing medium, and in photo- imine: graphic emulsions. → C6H5OH HOC6H4CH=NH This then hydrolyzes to the aromatic alde- gel electrophoresis see electrophoresis. hyde: → HOC6H4CH=NH2 HOC6H4CHO gel filtration See molecular sieve. Similar reactions using alkyl cyanides (nitriles) rather than hydrogen cyanide give gem positions Positions in a molecule on aromatic ketones. This type of reaction, in the same atom. For example, 1,1- which a cyanide is used to produce an alde- dichloroethane (CH3CHCl2) is a gem di- hyde (or ketone) is often called the Gatter- halide. man reaction. The Gatterman–Koch reaction was reported by the German general formula A representation of the chemist Ludwig Gatterman (1860–1920) chemical formula common to a group of in 1897 (with J. C. Koch). The use of hy- compounds. For example, C H is the drogen cyanide was reported by Gatter- n 2n+2 general formula for an alkane, whose man in 1907. members form a homologous series. See also empirical formula; homologous series; Gatterman reaction 1. See Sandmeyer molecular formula; structural formula. reaction. 2. See Gatterman–Koch reaction. geochemistry /jee-oh-kem-iss-tree/ The gauche conformation /gohsh/ See con- study of the chemistry of the Earth. The formation. subject includes the chemical composition of the Earth, the abundance of the elements gauss /gows/ Symbol: G The unit of mag- and their isotopes, the atomic structure of netic flux density in the c.g.s. system. It is minerals, and chemical processes that equal to 10–4 tesla. occur at the high temperatures and pressures inside the Earth. Gay-Lussac’s law 1. Gases react in volumes that are in simple ratios to each other geometrical isomerism See isomerism. and to the products if they are gases (all volumes measured at the same temperature germanium /jer-may-nee-ŭm/ A hard and pressure). brittle gray metalloid element belonging to 2. See Charles’ law. group 14 (formerly IVA) of the periodic table. It is found in sulfide ores such as ar- gel /jel/ A lyophilic colloid that is normally gyrodite (4Ag2S.GeS2) and in zinc ores and stable but may be induced to coagulate coal. Most germanium is recovered during partially under certain conditions (e.g. zinc or copper refining as a by-product. lowering the temperature). This produces a Germanium was extensively used in early pseudo-solid or easily deformable jelly-like semiconductor devices but has now been mass, called a gel, in which intertwining largely superseded by silicon. It is used as

120 glutamine an alloying agent, catalyst, phosphor, and of the atoms on a lattice. It can be regarded in infrared equipment. as a supercooled liquid, which has not crys- Symbol: Ge; m.p. 937.45°C; b.p. tallized. Solids with similar noncrystalline 2830°C; r.d. 5.323 (20°C); p.n. 32; r.a.m. structures are also called glasses 72.61. Glauber’s salt /glow-ber, glaw-/ See germanium(IV) oxide (GeO2) A com- sodium sulfate. pound made by strongly heating germanium in air or by hydrolyzing GLC Gas-liquid chromatography. See gas germanium(IV) chloride. It occurs in two chromatography. forms. One is slightly soluble in water forming an acidic solution; the other is in- glove box A sealed box with gloves fitted soluble in water. Germanium oxide dis- to ports in one side and having a transpar- 2– solves in alkalis to form the anion GeO3 . ent top, used for safety reasons or to per- form experiments in an inert or sterile German silver See nickel-silver. atmosphere.

Gibbs function (Gibbs free energy) Sym- gluconic acid /gloo-kon-ik/ (dextronic bol: G A thermodynamic function defined acid CH2OH(CHOH)4COOH) A soluble by crystalline organic acid made by the oxida- G = H – TS tion of glucose (using specific molds). It is where H is the enthalpy, T the thermody- used in paint strippers. namic temperature, and S the entropy. It is useful for specifying the conditions of glucosan A POLYSACCHARIDE that is chemical equilibrium for reactions for con- formed of glucose units. Cellulose and stant temperature and pressure (G is a min- starch are examples. imum). The function is named for the American mathematician and theoretical glucose /gloo-kohs/ (dextrose; grape physicist Josiah Williard Gibbs sugar; C6H12O6) A monosaccharide oc- (1839–1903). See also free energy. curring widely in nature as D-glucose. It occurs as glucose units in sucrose, starch, and giga- Symbol: G A prefix denoting 109. cellulose. It is important to metabolism be- For example, 1 gigahertz (GHz) = 109 hertz cause it participates in energy-storage and (Hz). energy-release systems. See also sugar. glacial ethanoic (acetic) acid Pure glucoside /gloo-kŏ-sÿd/ See glycoside. water-free ethanoic acid. glue An adhesive, of which there are vari- glacial ethanoic acid (glacial acetic acid) ous types. Aqueous solutions of starch and Pure water-free ethanoic acid. ethyl cellulose are used as pastes for stick- ing paper; traditional wood glue is made by glass A hard transparent material made boiling animal bones (see gelatin); quick- by heating calcium oxide (lime), sodium drying adhesives are made by dissolving carbonate, and sand (silicon(IV) oxide). rubber or a synthetic polymer in a volatile This produces a calcium silicate – the nor- solvent; and some polymers, such as epoxy mal type of glass, called soda glass. Special resins and polyvinyl acetate (PVA), are types of glass can be obtained by incorpo- themselves used as glues. rating boron oxide in the glass (borosilicate glass, used for laboratory apparatus) glutamic acid /gloo-tam-ik/ See amino or by including metals other than calcium, acids. e.g. lead or barium. Glass is an amorphous substance, in the glutamine /gloo-tă-meen, -min/ See amino sense that there is no long-range ordering acids.

121 glyceride glyceride /gliss-ĕ-rÿd, -rid/ An ester leable. Gold is used in jewelry, often al- formed between glycerol (propane-1,2,3- loyed with copper, and in electronics and triol) and one or more carboxylic acids. colored glass. Pure gold is 24 carat; 9 carat Glycerol has three alcohol groups, and if indicates that 9 parts in 24 consist of gold. all three groups have formed esters, the Symbol: Au; m.p. 1064.43°C; b.p. compound is a triglyceride. Naturally oc- 2807°C; r.d. 19.320 (20°C); p.n. 79; r.a.m. curring fats and oils are triglycerides of 196.96654. long-chain carboxylic acids (hence the name ‘fatty acid’). The main carboxylic gold(III) chloride (gold trichloride; auric acids occurring in fats and oils are: chloride; AuCl3) A compound prepared by 1. octadecanoic acid (stearic acid), a satu- dissolving gold in aqua regia. The bright rated acid CH3(CH2)16COOH. yellow crystals (chloroauric acid) produced 2. hexadecanoic acid (palmitic acid), a sat- on evaporation are heated to form dark red urated acid CH3(CH2)14COOH. crystals of gold(III) chloride. The chloride 3. cis-9-octadecenoic acid (oleic acid), an decomposes easily (at 175°C) to give unsaturated acid. gold(I) chloride and chlorine; at higher CH3(CH2)7CH:CH(CH2)7COOH temperatures it decomposes to give gold and chlorine. Gold(III) chloride is used in gliss-ĕ-rin, -reen, gliss-ĕ-reen glycerine / / photography. It exists as a dimer, Au Cl . (glycerin) See propane-1,2,3-triol. 2 6 Goldschmidt process /gohld-shmit/ A glycerol /gliss-ĕ-rol, -rohl/ See propane- process for extracting certain metals from 1,2,3-triol. their oxides by reduction with aluminum. It is named for the German chemist Johann glyceryl trinitrate /gliss-ĕ-răl trÿ-nÿ-trayt/ (Hans) Wilhelm Goldschmidt (1861– See nitroglycerine. 1923). See thermite. glycine /glÿ-seen, glÿ-seen/ See amino /trÿ-klor-ÿd, -kloh-rÿd/ acids. gold trichloride See gold(III) chloride. glycogen /glÿ-kŏ-jĕn/ (animal starch) A polysaccharide that is the main carbohy- graft copolymer See polymerization. drate store of animals. It is composed of many glucose units linked in a similar way Graham’s law (of diffusion) The princi- to starch. Glycogen is readily hydrolyzed in ple that gases diffuse at a rate that is in- a stepwise manner to glucose itself. It is versely proportional to the square root of stored largely in the liver and in muscle but their density. Light molecules diffuse faster is found widely distributed in the body. than heavy molecules. The principle is used in the separation of isotopes. The law is glycol /glÿ-kol. -kohl/ See diol. named for the Scottish chemist Thomas Graham (1805–69). glycoside /glÿ-kŏ-sÿd/ A compound made by replacing a hydroxyl group of a mono- grain A crystal in a metal that has been saccharide sugar with an alcoholic, pheno- prevented from attaining its regular geo- lic, or other group. The bond is a glycosidic metrical form. link. If the sugar is glucose, the compound is a glucoside. Glycosides occur in plants . gram Symbol: g A unit of mass defined as 10–3 kilogram. glycosidic link /glÿ-kŏ-sid-ik/ See glycoside. gram-atom See mole. gold A transition metal that occurs native. gram-equivalent The equivalent weight It is unreactive and is very ductile and mal- of a substance in grams.

122 group 13 elements gram-molecule See mole. group and X is a halogen (e.g. CH3MgCl). Grignard reagents are prepared by reacting granulation A process for enlarging par- the haloalkane or haloaryl compound with ticles to improve the flow properties of magnesium in dry ether: → solid reactants and products in industrial CH3Cl + Mg CH3MgCl chemical processes. The larger a particle, Grignard reagents probably have the and the freer from fine materials in a solid, form R2Mg.MgCl2. They are used exten- the more easily it will flow. Dry granula- sively in organic chemistry. With methanal tion produces pellets from dry materials, a primary alcohol is produced: → which are crushed into the desired size. RMgX + HCHO RCH2OH + Wet granulation involves the addition of a Mg(OH)X liquid to the material, and the resulting Other aldehydes give secondary alcohols: ′ → ′ paste is extruded and dried before cutting RMgX + R CHO RR CHOH + into the required size. Mg(OH)X Alcohols and carboxylic acids give hydro- grape sugar See dextrose. carbons: RMgX + R′OH → RR′ + Mg(OH)X graphite An allotrope of CARBON. Water also gives a hydrocarbon: → Graphite is a good conductor of heat and RMgX + H2O RH + Mg(OH)X electricity. The atoms are arranged in lay- Solid carbon dioxide in acid solution gives a carboxylic acid: ers which cleave easily and graphite is used → as a solid lubricant. RMgX + CO2 + H2O RCOOH + Mg(OH)X gravimetric analysis /grav-ă-met-rik/ A The lowest energy state of method of quantitative analysis in which ground state an atom, molecule, or other system. Com- the final analytical measurement is made pare excited state. by weighing. There are many variations in the method but in essence they all consist group 1. In the PERIODIC TABLE, a series of of: chemically similar elements that have simi- 1. taking an accurately weighed sample lar electronic configurations. A group is into solution; thus a column of the periodic table. For ex- 2. precipitation as a known compound by ample, the alkali metals, all of which have a quantitative reaction; outer s1 configurations, belong to group 1. 3. digestion and coagulation procedures. 2. (FUNCTIONAL GROUP) In organic chem- 4. filtration and washing; istry, an arrangement of atoms that be- 5. drying and weighing as a pure com- stows a particular type of property on a pound. molecule and enables it to be placed in a Filtration is a key element in the particular class, e.g. the aldehyde group method and a variety of special filter pa- –CHO. pers and sinter-glass filters are available. group 0 elements See rare gases. gray Symbol: Gy The SI unit of absorbed energy dose per unit mass resulting from group 1 elements See alkali metals. the passage of ionizing radiation through living tissue. One gray is an energy absorp- group 2 elements See alkaline-earth met- tion of one joule per kilogram of mass. The als. unit is named for the British physician Harold Gray (1905–65). group 3-12 elements See transition elements. Grignard reagent /gree-nyar/ A type of organometallic compound with the general group 13 elements A group of elements formula RMgX, where R is an alkyl or aryl in the periodic table consisting of the ele-

123 group 14 elements ments boron (B), aluminum (Al), gallium shows the common trend towards metallic (Ga), indium (In), and thallium (T1). These character with the heavier elements; thus elements were formerly classified as group carbon is a typical non-metal, silicon and III elements and belonged to the IIIA sub- germanium are metalloids, and tin and group. The IIIB subgroup consisted of the lead are characteristically metallic. As ob- elements scandium (Sc), yttrium (Y), lan- served with other groups the first member thanum (La), and actinium (Ac). The of the group is quite different from the rest. group 13 elements all have three outer elec- The carbon atom is smaller and has a trons (s2p1) with no partly filled inner higher ionization potential, both favouring shells. The group is the first group of ele- predominance of covalence, but additional ments in the p-block. As with all the groups factors are: there is an increase in metallic character as 1. The widespread nature of extensive the group is descended. catenation in carbon compounds. The boron atom is both small and has a 2. The possibility of strong overlap of p or- high ionization potential, so bonds to bitals or double bonding. boron are largely covalent with only small 3. The unavailability of d orbitals in car- degrees of polarization. In fact boron is bon compounds. classed as a metalloid. It has volatile hy- Significant differences are: drides and a weakly acidic oxide. As the 1. Both oxides of carbon are gaseous, CO group is descended the ionization poten- and CO2; the other elements form solid tials decrease and the atomic radii increase, oxides, e.g. SiO2, Pb3O4. leading to increasingly polar interactions 2. The heavier elements have no com- and the formation of distinct M3+ ions. The pounds analogous to aromatic com- increase in metallic character is clearly il- pounds. lustrated by the hydroxides: boric acid 3. The heavier elements have no com- B(OH)3 is acidic; aluminum and gallium pounds analogous to ethene or ketones. hydroxides are amphoteric, dissolving in 4. The heavier elements readily expand 3+ 3+ 2– acids to give Al and Ga and in bases to their coordination number, e.g. SiF6 2– give aluminates and gallates; the hydrox- and SnCl6 . ides of indium and thallium are distinctly basic. As the elements get heavier the bond group 15 elements A group of elements energies with other elements become gen- in the periodic table consisting of the ele- erally smaller. The monovalent state (re- ments nitrogen (N), phosphorus (P), ar- moval of the p electron only) becomes senic (As), antimony (Sb), and bismuth progressively stable. For example gal- (Bi). These elements were formerly classi- lium(I) is known in the gas phase and in fied as group V elements and belonged to complex systems sometimes known as the VA subgroup. The VB subgroup con- ‘GaCl2’. Monovalent indium halides are sisted of the elements vanadium (V), nio- known, for example InX, and thallium(I) is bium (Nb), and tantalum (Ta), which are distinctly more stable than thallium(III). transition elements. The main-group elements all have elec- group 14 elements A group of elements tronic configurations corresponding to in the periodic table consisting of the ele- outer s2p3 with no vacancies in inner levels. ments carbon (C), silicon (Si), germanium The ionization potentials are high and the (Ge), tin (Sn), and lead (Pb). These ele- lighter members of the group, N and P, are ments were formerly classified as group IV distinctly electronegative and non-metallic elements and belonged to the IVA sub- in character. Arsenic and antimony are group. The IVB subgroup consisted of the metalloids and bismuth is weakly me- elements titanium (Ti), zirconium (Zr), and tallic (Bi2O3 dissolves in acids to give hafnium (Hf), which are transition metals. Bi(OH)3). The group 14 elements all have electronic Nitrogen is dissimilar from the other structures with four outer electrons (s2p2) members of the group in that it forms and no partly filled inner shells. The group stable multiple bonds, it is limited to coor-

124 GSC

+ dination number 4, e.g. NH4 , it is suffi- not expand its outer shell and positive oxi- ciently electronegative to form hydrogen dation states are uncommon for oxygen 3– + – bonds and the nitride ion N , and its ox- (OF2, O2F2, O2 PtF6 ). Oxygen is para- ides are irregular with the rest of the group. magnetic. Excluding oxygen, group 16 The group displays a remarkable num- shows similar trends with increasing size to ber of allotropes of its members showing those in group 15. For example decreasing the trend from non-metallic forms through stability of H2X, greater tendency to form 2– to metallic forms. Thus nitrogen has only complexes such as SeBr6 , decreasing sta- the diatomic form; phosphorus has a bility of high formal positive oxidation highly reactive form P1 (brown), and a states, and marginal metallic properties tetrahedral form P4 (white), forms based (e.g. Po forms a hydroxide). on broken tetrahedra Pn (red and violet), and a hexagonal layer-type lattice (black). group 17 elements A group of elements Arsenic and antimony have the As4 and Sb4 in the periodic table consisting of the ele- forms, which are less stable than the layer ments fluorine (F), chlorine (Cl), bromine type in this case; bismuth has the layer-lat- (Br), iodine (I), and astatine (At). Formerly tice form only. they belonged to group VII and were classified in the VIIA subgroup. The VIIB subgroup 16 elements A group of elements group consisted of the elements manganese of the periodic table sometimes called the (Mn), technetium (Te), and rhenium (Re), chalcogens, consisting of the elements oxy- which are transition elements. See halogen (O), sulfur (S), selenium (Se), tellurium gens. (Te), and polonium (Po). These elements were formerly classified as group VI ele- group 18 elements See rare gases. ments and belonged to the VIA subgroup. The VIB subgroup consisted of the ele- group theory A branch of mathematics ments chromium (Cr), molybdenum (Mo), used to analyze symmetry in a systematic and tungsten (W), which are transition ele- way. A group consists of a set of elements ments. The electronic configurations of the A, B, C, etc. and a rule for forming the group 6 elements are all s2p4 with no va- product of these elements, such that certain cant inner orbitals. These configurations conditions are satisfied: are all just two electrons short of a rare gas (1) Every product AB of two elements A structure, consequently they have high and B is also an element of the set. electron affinities and are almost entirely (2) Any three elements A, B, C, must satify non-metallic in character. A(BC) = (AB)C. The group shows the normal property (3) There is an element of the set, denoted of a trend towards metallic character as it I, which is the identity element, i.e. for all is descended. Selenium, tellurium and polo- A in the set AI = IA =A. nium have ‘metallic’ allotropes and po- (4) For each element A of the set there is an lonium has generally metalloid-type inverse, denoted A–1, which also belongs to properties where they have been studied the set which satisfies the relation AA–1 = (Po is very rare). All the elements combine A–1 = A = I. with a large number of other elements, In the case of symmetry operations the both metallic and non-metallic, but in con- product is the successive performance of trast to compounds of the halogens they these operations. If a group has a finite are more generally insoluble in water, and number of elements it is said to be a dis- even where soluble they do not ionize read- crete group. The point groups, which arise ily. from the rotations and reflections of bodies Oxygen behaves like the first members such as isolated molecules are discrete of other groups in having great differences groups. from the rest of the group. For example, oxygen forms hydrogen bonds whereas GSC Gas–solid chromatography. See gas sulfur and the others do not; oxygen can- chromatography.

125 guanidine guanidine /gwan-ă-deen, -din, gwah-nă-/ gun cotton See cellulose trinitrate. (iminourea; HN:C(NH2)2) A strongly basic crystalline organic compound which gunmetal See bronze. can be nitrated to make a powerful explosive. It is also used in making dyestuffs, gunpowder A powdered mixture of sul- medicines and polymer resins. fur, charcoal, and potassium nitrate, used as an explosive. guanine /gwah-neen, -nin/ A nitrogenous gypsum /jip-sŭm/ See calcium sulfate. base found in DNA and RNA. Guanine has a purine ring structure. gyromagnetic ratio /jÿ-roh-mag-net-ik/ The ratio of the magnetic moment of a sys- guanosine /gwah-nŏ-seen, -sin/ (guanine tem to the angular momentum of that sys- nucleoside) A NUCLEOSIDE present in DNA tem. The gyromagnetic ratio is a useful and RNA and consisting of guanine linked quantity in the theory of electrons and to D-ribose via a β-glycosidic bond. atomic nuclei.

126 H

Haber process /hay-ber/ An important e.m.f. set up between electrode and solu- industrial process for the manufacture of tion by transfer of electrons to or from the ammonia, which is used for fertilizers and electrode. The e.m.f. of a half cell cannot for making nitric acid. The reaction is the be measured directly since setting up a cir- equilibrium: cuit results in the formation of another half ˆ N2 + 3H2 3NH3 cell. See electrode potential. The nitrogen used is obtained by fractionation of liquid air and the hydrogen by the half-life (half-life period; Symbol: t½) The oxidation of hydrocarbons (from natural time taken for half the nuclei of a sample of gas). The nitrogen and hydrogen are puri- a radioactive nuclide to decay. The half-life fied and mixed in the correct proportions. of a nuclide is a measure of its stability. The equilibrium amount of ammonia is (Stable nuclei can be thought of as having favoured by low temperatures, but in prac- infinitely long half-lives.) If N0 is the origi- tice the reaction would never reach equilib- nal number of nuclei, the number remain- rium at normal temperatures. An optimum ing at the end of one half-life is N0/2, at the ° temperature of about 450 C is therefore end of two half-lives is N0/4, etc. used. High pressure also favors the reaction and a pressure of about 250 atmos- half-sandwich compound See sandwich pheres is used. The catalyst is iron with compound. small amounts of potassium and aluminum oxides present. The yield is about 15%. halide /hal-ÿd, hay-lÿd/ A compound con- Ammonia is condensed out of the gas mix- taining a halogen. The inorganic halides of ture at –50°C. The process is named for the electropositive elements contain ions of the German physical chemist Fritz Haber type Na+Cl– (sodium chloride) or K+Br– (1868–1934). (potassium bromide). Transition metal halides often have some covalent bonding. habit See crystal habit. Non-metal halides are covalent compounds, which are usually volatile. Exam- hafnium /haf-nee-ŭm/ A transition metal ples are tetrachloromethane (CCl4) and found in zirconium ores. Hafnium is diffi- silicon tetrachloride (SiCl4). Halides are cult to work and can burn in air. It is used named as bromides, chlorides, fluorides, or in control rods for nuclear reactors and in iodides. certain specialized alloys and ceramics. Symbol: Hf; m.p. 2230°C; b.p. 5197°C; halite /hal-ÿt, hay-lÿt/ (rock salt) A natu- r.d. 13.31 (20°C); p.n. 72; r.a.m. 178.49. rally occurring mineral form of sodium chloride, NaCl. It forms colorless or white hahnium /hah-nee-ŭm/ Symbol: Ha or Hn crystals when pure, but is often colored by A name formerly suggested for element- impurities. 105 (dubnium) and also for element-108 (hassium). See element. haloalkane /hal-oh-al-kayn/ (alkyl halide) A type of organic compound in which one half cell An electrode in contact with a so- or more hydrogen atoms of an alkane have lution of ions. In general there will be an been replaced by halogen atoms. Haloalka-

127 halobutyl nes can be made by direct reaction of the and chlorine. They are useful as refriger- alkane with a halogen. Other methods are: ants, aerosol propellants, and in making 1. Reaction of an alcohol with the halogen rigid plastic foams. However, they are also acid (e.g. from NaBr + H2SO4) or with thought to damage the ozone layer and an phosphorus halides (red phosphorus international agreement exists to phase out and iodine can be used): their use. Similar compounds are the hy- → ROH + HBr RBr + H2O drochlorofluorocarbons (HCFCs), which → ROH + PCl5 RCl + POCl3 + HCl contain hydrogen as well as chlorine and 2. Addition of an acid to an alkene: fluorine, and the hydrofluorocarbons → RCH:CH2 + HBr RCH2CH2Br (HFCs), which contain hydrogen and fluo- The haloalkanes are much more reac- rine. tive than the alkanes, and are useful start- The halons are a class of halocarbons ing compounds for preparing a wide range that contain bromine as well as hydrogen of organic chemicals. In particular, they and other halogens. Their main use is in undergo nucleophilic substitutions in fire extinguishers. They are, however, sig- which the halogen atom is replaced by nificantly more active than CFCs in their some other group (iodine compounds are effect on the ozone layer. The halocarbons the most reactive). Some reactions of are also thought to contribute to global haloalkanes are: warming. 1. Refluxing with aqueous potassium hydroxide to give an alcohol: haloform /hal-ŏ-form/ Any of the four – → – RI + OH ROH + I compounds CHX3, where X is a halogen 2. Refluxing with potassium cyanide in al- atom (F, fluoroform; Cl, chloroform; Br, coholic solution to give a nitrile: bromoform; I, iodoform). The systematic RI + CN– → RCN + I– names are fluoromethane, chloromethane, 3. Refluxing with an alkoxide to give an bromomethane, and iodomethane. See also ether: haloform reaction. RI + –OR′→ROR′ + I– 4. Reaction with alcoholic ammonia solu- haloform reaction A reaction of a tion (100°C in a sealed tube) to give an methyl ketone with NaOX, where X is Cl, amine: Br, or I, to give a haloform. With sodium → RI + NH3 RNH2 + HI chlorate(I), for example: → 5. Boiling with alcoholic potassium hy- RCOCH3 + 3NaOCl RCOCCl3 + droxide, to eliminate an acid and pro- 3NaOH → duce an alkene: RCOCl3 + NaOH NaOCOR + → RCH2CH2I + KOH KI + H2O + CHCl3 RCH:CH2 The reaction can be used to make car- See also Fittig reaction; Grignard boxylic acids (from the NaOCOR), and is reagent; Wurtz reaction. especially useful when R is an aromatic group because the starting ketone, halobutyl /hal -oh-byoo-t’l/ See butyl rub- RCOCH3, can be produced by Friedel– ber. Crafts acetylation. See also triiodomethane. halocarbons /hal-oh-kar-bŏnz/ Chemical compounds that contain carbon atoms halogenating agent /hal-lŏ-jĕ-nayt-ing/ A bound to halogen atoms and (sometimes) compound used to introduce halogen hydrogen atoms. The halocarbons include atoms into a molecule. Examples are phos- haloalkanes such as tetrachloromethane phorus trichloride (PCl3) and aluminum (CCl4) and the haloforms (CHCl3, CHBr3, trichloride (AlCl3). etc.). There are various types of halocarbon that are useful but are also significant halogenation /hal-ŏ-jĕ-nay-shŏn/ A reac- pollutants. For example, the chlorofluoro- tion in which a halogen atom is introduced carbons (CFCs) contain carbon, fluorine, into a molecule. Halogenations are speci-

128 hardening fied as chlorinations, brominations, fluori- chlorine and iodine also forming +3 and +7 nations, etc., according to the element in- species (e.g. HOCl, HBrO3, I2O5, HIO4). volved. There are several methods. The elements decrease in oxidizing > > > 1. Direct reaction with the element using power in the order F2 Cl2 Br2 I2 and the high temperature or ultraviolet radia- ions X– may be arranged in order of in- tion: creasing reducing power F–

129 hardness

∆ Š terol build-up in the body, and consequent symbol HM . The superscript symbol de- risk of coronary heart disease. The hydro- notes standard conditions, while the sub- genation process may, however, also affect script M indicates that the enthalpy change the nature of the double bonds. Natural is for one mole. The unit is usually the kilo- unsaturated fatty acids mostly have a cis joule per mole (kJ mol–1). By convention, configuration about the double bonds. In ∆H is negative for an exothermic reaction. the hydrogenation process, a proportion of Molar enthalpy changes stated for chemi- these are converted into fatty acids with a cal reactions are changes for standard con- trans configuration. Glycerides of these are ditions, which are defined as 298 K (25°C) known as trans-fats. It has been claimed and 101 325 Pa (1 atmosphere). Thus, the that there is also a link between trans-fats standard molar enthalpy of reaction is the and coronary heart disease. See also enthalpy change for reaction of substances Sabatier–Senderens process. under these conditions producing reactants under the same conditions. The substances hardness (of water) Hard water is water that will not readily form a lather with involved must be in their normal equilibrium physical states under these conditions SOAP owing to the presence of dissolved calcium, iron, and magnesium compounds. (e.g. carbon as graphite, water as the liq- Such compounds can react with soap to uid, etc.). Note that the measured enthalpy produce insoluble salts, which collect as change will not usually be the standard solid scum. The effectiveness of the cleans- change. In addition, it is common to spec- ing solution is thus reduced. Hardness of ify the entity involved. For instance ∆ Š water is of two types, TEMPORARY HARD- Hf (H2O) is the standard molar en- NESS and PERMANENT HARDNESS. Only tem- thalpy of formation for one mole of H2O porary hardness can be removed by boiling species. the water. Hardness of water is usually expressed heat engine (thermodynamic engine) A by assuming that all the hardness is due to device for converting heat energy into dissolved calcium carbonate, which is pre- work. Heat engines operate by transferring sent as ions. It can be estimated by titration energy from a high-temperature source to a with a standard soap solution or with edta. low-temperature sink. The theoretical op- See also water softening. eration of heat engines is useful in the theory of thermodynamics. See Carnot cycle. hard vacuum See vacuum. heat exchangers Devices that enable the hard water See hardness. heat from a hot fluid to be transferred to a cool fluid without allowing them to come hassium /hass-ee-ŭm/ A transactinide ele- into contact. The normal arrangement is ment that is formed artificially. for one of the fluids to flow in a coiled tube Symbol: Hs; p.n. 108; most stable iso- through a jacket containing the second tope 265Hs (half-life 2 × 10–3s). fluid. Both the cooling and heating effect HCFC Hydrochlorofluorocarbon. See may be of benefit in conserving the energy halocarbon. used in a chemical plant and in controlling the process. heat Energy transferred as a result of a temperature difference. The term is often heat of atomization The energy required loosely used to mean internal energy (i.e. in dissociating one mole of a substance into the total kinetic and potential energy of the atoms. See heat. particles). It is common in chemistry to define such quantities as heat of combustion, heat of combustion The energy liberated heat of neutralization, etc. These are in fact when one mole of a substance burns in ex- molar enthalpies for the change, given the cess oxygen. See heat.

130 helium heat of crystallization The energy liber- constant. The uncertainty principle is ated when one mole of a substance crystal- named for the German physicist Werner lizes from a saturated solution of this Karl Heisenberg (1901–76). substance. helicate /hel-ă-kayt/ See supramolecular heat of dissociation The energy required chemistry. to dissociate one mole of a substance into its constituent elements. helium /hee-lee-ŭm/ A colorless monatomic gas; the first member of the heat of formation The energy change rare gases (group 18 of the periodic table). when one mole of a substance is formed Helium has the electronic configuration from its elements. See heat. 1s2 and consists of a nucleus of two protons and two neutrons (equivalent to an α- heat of neutralization The energy liber- particle) with two extra-nuclear electrons. ated when one mole of an acid or base is It has an extremely high ionization poten- neutralized. tial and is completely resistant to chemical attack of any sort. The gas accounts for heat of reaction The energy change when only 5.2 × 10–4% of the atmosphere; up to molar amounts of given substances react 7% occurs in some natural gas deposits. completely. See heat. Helium is the second most abundant element in the universe, the primary process heat of solution The energy change when on the Sun being nuclear fusion of hydro- one mole of a substance is dissolved in a gen to give helium. given solvent to infinite dilution (in prac- Helium is recovered commercially from tice, to form a dilute solution). natural gas in both the USA and countries of the former USSR and it also forms part heavy hydrogen See deuterium. of ammonia plant tail gas if natural gas is used as a feedstock. Its applications are in heavy-metal pollution See pollution. fields in which inertness is required and where the cheaper alternatives, such as heavy water Deuterium oxide, D2O. nitrogen, are too reactive; for example, high-temperature metallurgy, powder tech- hecto- Symbol: h A prefix denoting 102. nology, and as a coolant in nuclear reac- For example, 1 hectometer (hm) = 102 me- tors. Helium is also favoured over nitrogen ters (m). for diluting oxygen for deep-sea diving (lower solubility in blood) and as a pres- Heisenberg’s uncertainty principle /hÿ- surizer for liquefied gas fuels in rockets zĕn-bergz/ The impossibility of making si- (total inertness). It is also used as an ideal multaneous measurements of both the gas for balloons (no fire risk) and for low- position and the momentum of a sub- temperature physics research. atomic particle (e.g. an electron) with un- Helium is unusual in that it is the only limited accuracy. The uncertainty arises known substance for which there is no because, in order to detect the particle, ra- triple point (i.e., no combination of pres- diation has to be ‘bounced’ off it, and this sure and temperature at which all three process itself disrupts the particle’s posi- phases can co-exist). This is because the in- tion. Heisenberg’s uncertainty principle is teratomic forces, which normally partici- not a consequence of ‘experimental error’. pate in the formation of solids, are so weak It represents a fundamental limit to objec- that they are of the same order as the zero- tive scientific observation, and arises from point energy. At 2.2 K helium undergoes a the wave–particle duality of particles and transition from liquid helium I to liquid radiation. In one direction, the uncertainty helium II, the latter being a true liquid but in position ∆x and momentum ∆p are re- exhibiting superconductivity and an im- lated by ∆x∆p∼h/4π, where h is the Planck measurably low viscosity (superfluidity).

131 Hell–Volhard–Zelinsky reaction

The low viscosity allows the liquid to water of crystallization per two molecules spread in layers a few atoms thick, de- of compound (e.g. 2CaSO4.H2O). scribed by some as ‘flowing uphill’. Helium also has an isotope. 3He is hemiketal /hem-ee-kee-t’l/ See ketal. formed in nuclear reactions and by decay of tritium. This also undergoes a phase hemimorphite /hem-ee-mor-fÿt/ See change at temperatures close to absolute calamine. zero. Symbol: He; m.p. 0.95 K (pressure); hemoglobin /hee-mŏ-gloh-bin, hem-ŏ-, b.p. 4.216 K; d. 0.1785 kg m–3 (0°C); p.n. hee-mŏ-gloh-bin/ The pigment of the red 2; r.a.m. 4.002602. blood cells that is responsible for the transport of oxygen from the lungs to the tis- Hell–Volhard–Zelinsky reaction /hell sues. It consists of a basic protein, globin, voh-lard zem-lin-skee/ A method for the linked with four heme groups. Heme is a preparation of halogenated carboxylic complex compound containing an iron acids using free halogen in the presence of atom. a phosphorus halide. The halogenation oc- The most important property of hemo- curs at the carbon atom adjacent to the globin is its ability to combine reversibly –COOH group. With Br2 and PBr3: with one molecule of oxygen per iron atom → → RCH2COOH RCHBrCOOH to form oxyhemoglobin, which has a RCBr2COOH bright red color. The iron is present in the The reaction is named for the German divalent state (iron(II)) and this remains chemists Carl Magnus von Hell (1849– unchanged with the binding of oxygen. 1926) and Jacob Volhard (1834–1910) There are variations in the polypeptide and for the Russian chemist Nicolai (Niko- chains, giving rise to different types of he- lay Dmitrievich) Zelinsky (1861–1953). moglobins in different species. The binding of oxygen depends on the oxygen partial Helmholtz function (Helmholtz free en- pressure; high pressure favors formation of ergy) Symbol: F A thermodynamic func- oxyhemoglobin and low pressure favors tion defined by release of oxygen. F = U – TS where U is the internal energy, T the ther- henry /hen-ree/ Symbol: H The SI unit of modynamic temperature, and S the en- inductance, equal to the inductance of a tropy. It is a measure of the ability of a closed circuit that has a magnetic flux of system to do useful work in an isothermal one weber per ampere of current in the cir- process. The function is named for the Ger- cuit. 1 H = 1 Wb A–1. The unit is named for man physiologist and theoretical physicist the American physicist Joseph Henry Herman Ludwig Ferdinand von Helmholtz (1797–1878). (1821–94). See also free energy. Henry’s law The concentration (C) of a hematite /hem-ă-tÿt, hee-mă-/ A mineral gas in solution is proportional to the par- form of iron(III) oxide. It is the principal tial pressure (p) of that gas in equilibrium ore of iron. with the solution, i.e. p = kC, where k is a proportionality constant. heme /heem/ (haeme) An iron-containing The relationship is similar in form to porphyrin that is the prosthetic group in that for Raoult’s law, which deals with hemoglobin, myoglobin, and some cyto- ideal solutions. chromes. A consequence of Henry’s law is that the ‘volume solubility’ of a gas is indepen- hemiacetal /hem-ee-ass-ĕ-tal/ See acetal. dent of pressure. hemihydrate /hem-ee-hÿ-drayt/ A crys- heparin /hep-ă-rin/ A POLYSACCHARIDE talline compound with one molecule of that inhibits the formation of thrombin

132 hexamine from prothrombin and thereby prevents heterolytic fission /het-ĕ-rŏ-lit-ik/ (het- the clotting of blood. It is used in medicine erolysis) The breaking of a covalent bond as an anticoagulant. so that both electrons of the bond remain with one fragment. A positive ion and a heptahydrate /hep-ta-hÿ-drayt/ A crys- negative ion are produced: talline hydrated compound containing one RX → R+ + X– molecule of compound per seven molecules Compare homolytic fission. of water of crystallization. heteropolymer See polymerization. heptane /hep-tayn/ (C7H16) A colorless liquid alkane obtained from petroleum re- hexacyanoferrate /heks-ă-sÿ-an-oh-fe- fining. It is used as a solvent. rayt/ See cyanoferrate. heptavalent /hep-tă-vay-lĕnt, hep-tav-ă-/ hexadecanoate /heks-ă-dek-ă-noh-ayt/ (septavalent) Having a valence of seven. (palmitate) A salt or ester of hexadecanoic acid. hertz /herts/ Symbol: Hz The SI unit of frequency, defined as one cycle per second hexadecanoic acid /heks-ă-dek-ă-noh-ik/ (s–1). Note that the hertz is used for regu- (palmitic acid) A crystalline carboxylic larly repeated processes, such as vibration acid: or wave motion. The unit is named for the CH3(CH2)14COOH German physicist Heinrich Rudolph Hertz It is present as GLYCERIDES in fats and oils. (1857–94). hexagonal close-packed crystal /heks- Hess’s law A derivative of the first law of ag-ŏ-năl/ A crystal structure in which lay- thermodynamics. It states that the total ers of close-packed atoms are stacked in an heat change for a given chemical reaction ABABAB arrangement. The second layer B involving alternative series of steps is inde- fits into the holes of the first layer A, with pendent of the route taken and is some- the third layer over the first. The coordina- times known as the law of constant heat tion number is 12. Zinc and magnesium summation. The law is named for the have hexagonal close-packed structures. Swiss–Russian chemist Germain Henri The unit cell is based on a hexagon with Hess (1802–50). atoms occupying corner and mid positions. See face-centered cubic crystal. hetero atom /het-ĕ-roh/ See heterocyclic compound. hexagonal crystal See crystal system. heterocyclic compound /het-ĕ-rŏ-sÿ- hexamethylene diamine /heks-ă-meth-ă- klik, -sik-lik/ A compound that has a ring leen dÿ-ă-meen/ See 1,6-diaminohexane. containing more than one type of atom. Commonly, heterocyclic compounds are hexamethylenetetramine /heks-ă-meth- organic compounds with at least one atom ă-leen-tet-ră-meen, -min/ See hexamine. in the ring that is not a carbon atom. Pyri- dine and glucose are examples. The non- hexamine /heks-ă-meen, -min/ (hexameth- carbon atom is called a hetero atom. ylenetetramine; C6H12N4) A white crys- Compare homocyclic compound. talline organic compound made by condensing methanal with ammonia. It is heterogeneous /het-ĕ-rŏ-jee-nee-ŭs/ Re- used as a fuel for camping stoves, in vul- lating to more than one phase. A heteroge- canizing rubber, and as a urinary disinfec- neous mixture, for instance, contains two tant. Hexamine can be nitrated to make the or more distinct phases. high explosive cyclonite.

133 hexane hexane /heks-ayn/ (C6H14) A liquid read off directly, the temperature is alkane obtained from the light fraction of known, and the pressure is obtained by crude oil. The principal use of hexane is in taking the atmospheric pressure minus the gasoline and as a solvent. mercury height in the barometer (with corrections for the density of mercury at hexanedioic acid /heks-ayn-dÿ-oh-ik/ higher temperatures). The method’s only (adipic acid; HOOC(CH2)4COOH) A col- advantage is that it may be used for sam- orless crystalline organic dicarboxylic acid ples that decompose at their normal boil- that occurs in rosin. It is used in the manu- ing point. See also Dumas’ method; Victor facture of NYLON. Meyer’s method. hexanoate /heks-ă-noh-ayt/ A salt or ester holmium /hohl-mee-ŭm/ A soft malleable of hexanoic acid. silvery element of the lanthanoid series of metals. It occurs in association with other hexanoic acid /heks-ă-noh-ik/ (caproic lanthanoids. It has few applications. acid, CH3(CH2)4COOH) An oily car- Symbol: Ho; m.p. 1474°C; b.p. boxylic acid found (as glycerides) in cow’s 2695°C; r.d. 8.795 (25°C); p.n. 67; r.a.m. milk and some vegetable oils. 164.93032. hexose /heks-ohs/ A SUGAR that has six HOMO /hoh-moh/ See frontier orbital. carbon atoms in its molecules. homocyclic compound /hoh-mŏ-sÿ-klik, /heks-ăl/ The group hexyl group hom-ŏ-/ A compound containing a ring C H CH –, having a straight chain of car- 5 11 2 made up of the same atoms. Benzene is an bon atoms. example of a homocyclic compound. Com- pare heterocyclic compound. HFC Hydrofluorocarbon. See halocarbon. homogeneous /hoh-mŏ-jee-nee-ŭs, hom- ŏ-/ Relating to a single phase. A homoge- histidine /his-tă-deen, -din/ See amino neous mixture, for instance, consists of acids. only one phase. Hofmann degradation /hoff-măn/ A method of preparing primary amines from homologous series A group of organic acid amides. The amide is refluxed with compounds possessing the same functional aqueous sodium hydroxide and bromine: group and having a regular structural pat- → tern so that each member of the series dif- RCONH2 + NaOH + Br2 fers from the next one by a fixed number of RCONHBr + NaBr + H2O – → – atoms. The members of a homologous se- RCONHBr + OH RCON Br + H2O RCON–Br → R–N = C = O + Br– ries can be represented by a general for- – → 2– mula. For example, the homologous series RNCO + 2OH RNH2 + CO2 The reaction is a ‘degradation’ in that a of alkane alcohols CH3OH, C2H5OH, carbon atom is removed from the amide C3H7OH, …, has a general formula chain. The degradation is named for the CnH2n+1OH. Each member differs by CH2 German organic chemist August Wilhelm from the next. Any two successive mem- von Hofman (1818–92). bers of a series are called homologs.

Hofmann’s method A rather outmoded homologs /hom-ŏ-lôgz/ See homologous method for determining the vapor density series. of volatile liquids. A known weight of sample is introduced into a mercury barometer homolytic fission /hoh-mŏ-lit-ik, hom- tube, which is surrounded by a heating ŏ-/ (homolysis) The breaking of a covalent jacket. The volume of vapor can thus be bond so that one electron from the bond is

134 hydride left on each fragment. Two free radicals re- bound up in a compound it is known as the sult: water of crystallization. RR′→R• + R′• Compare heterolytic fission. hydration /hÿ-dray-shŏn/ The solvation of such species as ions in water. homopolymer /hoh-mŏ-pol-i-mer, hom- ŏ-/ See polymerization. hydraulic cement See cement. hornblende /horn-blend/ A dark-colored hydrazine /hÿ-dră-zeen/ (N2H4) A color- rock-forming mineral consisting of silicates less liquid that can be prepared by the oxi- of calcium, iron, and magnesium. It is a dation of ammonia with sodium major component of granite and other ig- chlorate(I) or by the gas phase reaction of neous and metamorphic rocks. ammonia with chlorine. Hydrazine is a weak base, forming salts (e.g. N2H4.HCl) host–guest chemistry A branch of with strong acids. It is a powerful reducing SUPRAMOLECULAR CHEMISTRY in which a agent, reducing salts of the noble metals to molecular structure acts as a ‘host’ to hold the metal. Anhydrous hydrazine ignites an ion or molecule (the ‘guest’). The guest spontaneously in oxygen and reacts vio- may be coordinated to the host or may be lently with oxidizing agents. The aqueous trapped by its structure. For example, cal- solution, hydrazine hydrate, has been used ixarenes are compounds with cup-shaped as a fuel for jet engines and for rockets. See molecules that may accept guest molecules. also hydrazone. See also crown ethers. hydrazoic acid /hÿ-dră-zoh-ik/ (hydrogen HPLC High-performance liquid chro- azide; azoimide; HN3) A colorless liquid matography; a sensitive analytical tech- with a nauseating smell. It is highly poiso- nique, that is similar to gas–liquid nous and explodes in the presence of oxy- chromatography but using a liquid carrier. gen and oxidizing agents. It can be made by The carrier is specifically choosen for the distilling a mixture of sodium azide particular substance to be detected. (NaN3) and a dilute acid. It is usually used as an aqueous solution. The salts of hydra- Hückel rule /hyoo-kĕl/ See aromatic com- zoic acid (azides), especially lead azide pound. (Pb(N3)2), are used in detonators because of their ability to explode when given a me- humectant /hyoo-mek-tănt/ A hygro- chanical shock. scopic substance used to maintain moisture levels. Glycerol, mannitol, and sorbitol are hydrazone /hÿ-dră-zohn/ A type of or- commonly used in foodstuffs, tobacco, etc. ganic compound containing the C:NNH2 group, formed by the reaction between an Humphreys series /hum-freez/ See hydro- aldehyde or ketone and hydrazine (N2H4). gen atom spectrum. Derivatives of hydrazine are often used to produce crystalline products, which have Hund’s rule /hûnts/ A rule that states that sharp melting points that can be used to the electronic configuration in degenerate characterize the original aldehyde or ke- orbitals will have the minimum number of tone. Phenylhydrazine (C6H5NH.NH2), paired electrons. The rule is named for the for instance, produces phenylhydrazones. German physicist Friedrich Hund (1896–1997). hydride /hÿ-drÿd/ A compound of hydrogen. Ionic hydrides are formed with highly hybrid orbital See orbital. electropositive elements and contain the H– ion (hydride ion). Non-metals form cova- hydrate /hÿ-drayt/ A compound coordi- lent hydrides, as in methane (CH4) or nated with water molecules. When water is silane (SiH4). The boron hydrides are elec- 135 hydrobromic acid tron-deficient covalent compounds. Many hydrofluoric acid /hÿ-droh-floo-or-ik, - transition metals absorb hydrogen to form oh-rik/ (HF) A colorless liquid produced interstitial hydrides. by dissolving hydrogen fluoride in water. It is a weak acid, but will dissolve most sili- hydrobromic acid /hÿ-droh-broh-mik/ cates and hence can be used to etch glass. (HBr) A colorless liquid produced by As the interatomic distance in HF is rela- adding hydrogen bromide to water. It tively small, the H–F bond energy is very shows the typical properties of a strong high and hydrogen fluoride is not a good acid and it is a strong reducing agent. A proton donor. It does, however, form hy- convenient way of producing hydrobromic drogen bonds. See hydrogen fluoride. – un- acid is to bubble hydrogen sulfide through able to donate protons easily – bromine water. Although it is not as strong hydrofluoric acid is a weak acid. See bond as hydrochloric acid it dissociates exten- energy. sively in water and is a good proton donor. hydrofluorocarbon /hÿ-droh-floo-ŏ-rŏ- hydrocarbon /hÿ-droh-kar-bŏn/ Any kar-bŏn/ See halocarbon. compound containing only the elements carbon and hydrogen. Examples are the hydrogen /hÿ-drŏ-jĕn/ A colorless gaseous alkanes, alkenes, alkynes, and aromatics element. Hydrogen has some similarities to such as benzene and naphthalene. both the alkali metals (group 1) and the halogens (group 17), but is not normally hydrochloric acid /hÿ-droh-klor-ik, - classified in any particular group of the pe- kloh-rik/ (HCl) A colorless fuming liquid riodic table. It is the most abundant element in the Universe and the ninth most made by adding hydrogen chloride to abundant element in the Earth’s crust and water: atmosphere (by mass). It occurs principally HCl(g) + H O1. → H O+(aq) + Cl–(aq) 2 3 in the form of water and petroleum prod- Dissociation into ions is extensive and ucts; traces of molecular hydrogen are hydrochloric acid shows the typical prop- found in some natural gases and in the erties of a strong acid. It reacts with car- upper atmosphere. bonates to give carbon dioxide and yields The gas may be prepared in the labora- hydrogen when reacted with all but the tory by the reaction of dilute hydrochloric most unreactive metals. Hydrochloric acid acid with a metal that lies above hydrogen is used in the manufacture of dyes, drugs, in the electromotive series, magnesium and and photographic materials. It is also used zinc being commonly used: to pickle metals, i.e. clean the surface prior → Zn + 2HCl H2 + ZnCl2 to electroplating. Hydrochloric acid do- Reactions of the amphoteric metals zinc nates protons with ease and is the strongest and aluminum with dilute aqueous alkali, of the hydrohalic acids. The concentrated to form zincates or aluminates, are also a acid is oxidized to chlorine by such agents convenient source of hydrogen. Electroly- as potassium manganate(VII) and man- sis of dilute mineral acids may be used to ganese(IV) oxide. obtain hydrogen but care must be taken to avoid mixing with the oxygen released at hydrochlorofluorocarbon /hÿ-droh- the anode as this leads to explosive mix- klor-ŏ-floo-ŏ-rŏ-kar-bŏn, -kloh-roh-/ See tures. Industrially, hydrogen is obtained as halocarbon. a by-product of the electrolytic cells used in the production of sodium hydroxide (reac- hydrocyanic acid /hÿ-droh-sÿ-an-ik/ tion of the Na/Hg amalgam with water), or (prussic acid; HCN) A highly poisonous by the water-gas route in which steam is weak acid formed when hydrogen cyanide decomposed by hot coke. gas dissolves in water. Its salts are The main use of hydrogen is as a chem- cyanides. Hydrogen cyanide is used in ical feedstock for the manufacture of am- making acrylic plastics. monia and of a range of organic

136 hydrogen compounds. Small-scale uses include re- ticular is renowned for its ability to absorb ducing atmospheres for metallurgy, hard- hydrogen as PdHx, where x takes values up ening edible oils, and pharmaceutical to 1.8. Titanium and zirconium behave manufacture. Hydrogen also has a poten- similarly but the exact nature of the com- tial future use as a fuel. pounds formed and of the bond type re- Hydrogen occupies a unique position mains uncertain. There are changes in the among the elements as hydrogen atoms are magnetic properties of the metal (indicat- the simplest of all atoms. The hydrogen ing some electron interaction) and in the atom consists of a proton (positive charge) lattice dimensions but discrete phases of with one extranuclear electron (1s1). The the type MH or MH2 are not isolated. The chemistry of hydrogen depends on one of class is sometimes referred to as the inter- three processes: stitial hydrides. 1. Loss of the electron to form H+. Atomic nuclei possess the property of 2. Gain of an electron to form H–. ‘spin’ and for diatomic molecules there ex- 3. Sharing of electrons by covalent bond ists the possibility of having the spins of ad- formation as in H2 or HCl. The hydrogen atom with the 1s electron jacent nuclei aligned (ortho) or opposed removed would have an extremely small (para). Because of the small mass of hydro- ionic radius and the positive hydrogen ion gen, these forms are more important in hy- occurs only in association with other drogen molecules than in other diatomic + + molecules. The two forms are in equilib- species as in H NH3 or H FH. The ion commonly written H+ in solution is in fact rium with parahydrogen dominant at low the solvated proton (hydroxonium or hy- temperatures, rising to 75% orthohydro- + dronium) H3O , which is formed by ion- gen at room temperatures. Although chem- ization of acids: ically identical the melting point and → + – H2O + HCl H3O + Cl boiling point of the para form are both It is believed that the lifetime of any one about 0.1° lower than the 3:1 equilibrium + H3O ion is extremely short as the protons mixture. appear to undergo very rapid exchange be- Natural hydrogen in molecular or com- tween water molecules. bined forms contains about one part in Hydrogen also forms a number of com- 2000 of deuterium, D, an isotope of hy- pounds in which it is regarded as gaining drogen that contains one proton and one – an electron and becoming H (the hydride neutron in its nucleus. Although the effect ion). It can form ionic hydrides only with of isotopes on chemical properties is nor- the most electropositive elements (groups 1 mally small, in the case of hydrogen the dif- and 2). The ionic nature of these com- ference in mass number leads to a lowering pounds is indicated by the fact that the of some reaction rates known as the ‘deu- melts are good conductors and that elec- terium isotope effect’. Hydrogen also ex- trolysis liberates hydrogen at the anode. hibits two less common forms of bonding. These hydrides are prepared by heating the Boron hydrides form a wide variety of element in a stream of hydrogen: compounds in which the hydrogen acts as H + 2M → 2MH 2 a bridging species involving ‘three-centre Examples are CH4, NH3, and HCl. These compounds are generally low-boil- two-electron’ bonds. Such species are said ing. General methods of preparation are: to be ‘electron deficient’ as they do not 1. The hydrolysis of the appropriate ‘-ide’ have sufficient electrons for conventional compound; e.g. silicides give silane, ni- two-electron covalent bonds. The second, less common, form is that of the coordi- trides give ammonia, sulfides give H2S. 2. Reduction of a chloride; for example: nated hydrides in which the H– ion acts as → SiCl4 + LiAlH4 SiH4 + LiCl + AlCl3 a ligand bound to a transition metal atom. A third class of hydride is that of metal- Symbol: H; m.p. 14.01 K; b.p. 20.28 K; lic hydrides formed between hydrogen and d. 0.089 88 kg m–3 (0°C); p.n. 1; r.a.m. many transition metals. Palladium in par- 1.0079.

137 hydrogenation hydrogenation /hÿ-droj-ĕ-nay-shŏn/ The by the electronegative element X leads to a reaction of a compound with hydrogen. An positive charge on hydrogen Xδ––Hδ+; this example is the hydrogenation of nitrogen hydrogen can then interact directly with to form ammonia in the Haber process. In electronegative elements of adjacent mole- organic chemistry, hydrogenation refers to cules. The hydrogen bond is represented as the addition of hydrogen to multiple a dotted line: bonds, usually with the aid of a catalyst. Xδ– – Hδ+ ...... Xδ– – Hδ+ … Unsaturated natural liquid vegetable oils The length of a hydrogen bond is charac- can be hydrogenated to form saturated teristically 0.15–0.2 nm. Hydrogen bond- semisolid fats – a reaction used in making ing may lead to the formation of dimers types of margarine. See Bergius process; (for example, in carboxylic acids) and is hardening. used to explain the anomalously high boiling points of H2O and HF. hydrogen atom spectrum The spectrum of the hydrogen atom is characterized by hydrogen bromide (HBr) A colorless several series of sharp spectral lines de- sharp-smelling gas that is very soluble in scribed by simple laws. The general law for water. It is produced by direct combination these series of lines is: of hydrogen and bromine in the presence of λ 2 2 1/ = R (1/n 1 – 1/n 2), a platinum catalyst or by the reaction of where λ is the wavelength associated with phosphorus tribromide with water. It dis- a spectral line, R is the RYDBERG CONSTANT solves in water to give hydrobromic acid. ≥ and n1 and n2 are integers, with n2 n1. Hydrogen bromide is rather inactive chem- The first of these series to be discovered ically. It will not conduct electricity in the was the BALMER SERIES in which n1 = 2, n2 = liquid state, indicating that it is a molecu- 3,4,5,… This series is in the visible region lar compound. and was discovered by the Swiss mathematician and physicist Johann Jakob hydrogencarbonate /hÿ-drŏ-jĕn-kar-bŏ- Balmer (1825–1898) in 1885. The series in nayt/ (bicarbonate) A salt containing the – which n1 = 1 is the LYMAN SERIES which lies ion HCO3. in the ultraviolet region. This series was discovered by the American physicist hydrogen chloride (HCl) A colorless gas Theodore Lyman (1874–1954). The that has a strong irritating odor and fumes Lyman series is a conspicuous feature of strongly in moist air. It is prepared by the the spectrum of the Sun. action of concentrated sulfuric acid on In the PASCHEN SERIES (n1 = 3), the sodium chloride. The gas is made industri- Brackett series (n1 = 4), the Pfund series (n1 ally by burning a stream of hydrogen in = 5) and the Humphreys series (n1 = 6) the chlorine. It is not particularly reactive but spectral lines occur in the infrared region. will form dense white clouds of ammo- The explanation for these regular series nium chloride when mixed with ammonia. lies in the existence of discrete, quantized It is very soluble in water and ionizes al- energy levels. In 1913 Niels Bohr was able most completely to give HYDROCHLORIC to derive the formula for these series in ACID. It will also dissolve in many non- terms of the ad hoc quantum assumptions aqueous solvents, including toluene, but of the BOHR THEORY. In the mid-1920s the will not ionize and the resultant solution formula was derived in a deductive way shows no acidic properties. Hydrogen from quantum mechanics. chloride is used in the manufacture of organic chlorine compounds, such as hydrogen azide See hydrazoic acid. polyvinyl chloride (PVC). Unlike the other hydrogen halides hy- hydrogen bond (H-bonding) An inter- drogen chloride will not dissociate on heat- molecular bond between molecules in ing, indicating a strong H–Cl bond. which hydrogen is bound to a strongly electronegative element. Bond polarization hydrogen cyanide See hydrocyanic acid.

138 hydrohalic hydrogen electrode A type of half cell contact with bases such as manganese(IV) based on hydrogen, and assigned zero oxide it gives off oxygen, the ELECTRODE POTENTIAL, so that other ele- manganese(IV) oxide acting as a catalyst: → ments may be compared with it. It is also 2H2O2 2H2O + O2 called the standard hydrogen half cell. The Hydrogen peroxide can act as an oxi- hydrogen is bubbled over a platinum elec- dizing agent, converting iron(II) ions to trode, coated in ‘platinum black’, in a 1 M iron(III) ions, or as a reducing agent with acid solution. Hydrogen is adsorbed on the potassium manganate(VII). It is used as a platinum black, which has a high surface bleach and in rocket fuel. The strength of area, enabling the equilibrium solutions is usually given as volume H(g) ˆ H+(aq) + e– strength – the volume of oxygen (dm3) at to be set up. The platinum is inert and has STP given by decomposition of 1 dm3 of no tendency to form platinum ions in solu- the solution. tion. hydrogensulfate /hÿ-drŏ-jĕn-sul-fayt/ hydrogen fluoride (HF) A colorless li- – quid produced by the reaction of concen- (bisulfate; HSO4 ) An acidic salt or ester of trated sulfuric acid on calcium fluoride: sulfuric acid (H2SO4), in which only one of → the acid’s hydrogen atoms has been re- CaF2(s) + H2SO4(aq) CaSO4(aq) + 2HF(l) placed by a metal or organic radical. An It produces toxic corrosive fumes and dis- example is sodium hydrogensulfate, solves readily in water to give hydrofluoric NaHSO4. acid. Hydrogen fluoride is atypical of the hy- hydrogen sulfide (sulfuretted hydrogen; drogen halides as the individual H–F units H2S) A colorless very poisonous gas with are associated into much larger units, an odor of bad eggs. Hydrogen sulfide is forming zigzag chains and rings. This is prepared by reacting hydrochloric acid caused by hydrogen bonds that form be- with iron(II) sulfide. It is tested for by mix- tween the hydrogen and the highly elec- ing with lead nitrate, with which it gives a tronegative fluoride ions. Hydrogen black precipitate. Its aqueous solution is fluoride is used extensively as a catalyst in weakly acidic. Hydrogen sulfide reduces the petroleum industry. See hydrofluoric iron(III) chloride to iron(II) chloride, form- acid. ing hydrochloric acid and a yellow precipitate of sulfur. Hydrogen sulfide hydrogen ion A positively charged hy- precipitates insoluble sulfides, and is used + drogen atom, H , i.e. a proton. Hydrogen in qualitative analysis. It burns with a blue ions are produced by all ACIDS in water, in flame in oxygen to form sulfur(IV) oxide which they are hydrated to hydroxonium and water. Natural gas contains some hy- (hydronium) ions, H O+. See pH. 3 drogen sulfide, which is removed before supply to the consumer. hydrogen molecule ion The simplest type of molecule. It consists of two hydrogen nuclei and one electron. If the nuclei hydrogensulfite /hÿ-drŏ-jĕn-sul-fÿt/ – are regarded as being fixed the (bisulfite; HSO3 ) An acidic salt or ester of SCHRÖDINGER EQUATION for the hydrogen sulfurous acid (H2SO3), in which only one molecule ion can be solved exactly. This of the acid’s hydrogen atoms has been re- enables theories and approximation tech- placed by a metal or organic radical. An niques concerned with chemical bonding example is sodium hydrogensulfite, to be tested quantitatively. NaHSO3. hydrogen peroxide (H2O2) A colorless hydrohalic /hÿ-droh-hal-ik/ Describing syrupy liquid, usually used in solution in acids formed by hydrogen halides, e.g. HF, water. Although it is stable when pure, on HCI, HBr, when dissolved in water.

139 hydroiodic acid hydroiodic acid /hÿ-droh-ÿ-od-ik/ See io- some hydroxides. It should not be con- dine. fused with the hydroxide ion (OH–). hydrolysis /hÿ-drol-ă-sis/ A reaction be- 2-hydroxypropanoic acid /hÿ-droks-ee- tween a compound and water. Some exam- proh-pă-noh-ok/ (lactic acid) A colorless ples are: liquid carboxylic acid: Salts of weak acids CH3CH(OH)COOH → Na2CO3 + 2H2O 2NaOH + H2CO3 See optical activity. Esters ˆ CH3COOC2H5 + H2O CH3COOH hygroscopic /hÿ-grŏ-skop-ik/ Describing + C2H5OH a substance that absorbs moisture from the Certain inorganic halides atmosphere. See also deliquescent. → SiCl4 + 4H2O Si(OH)4 + 4HCl hyperconjugation /hÿ-per-kon-jŭ-gay- hydron /hÿ-dron/ The positive ion H+. shŏn/ The interaction of sigma bonds with The name is used when the isotope is not pi bonds in a compound. It is sometimes relevant, i.e. a hydron could be a proton, described in terms of resonance structures deuteron, or triton. of the type: → – + C6H5CH3 C6H5CH2 H hydronium ion /hÿ-droh-nee-ŭm/ See to explain the interaction of the methyl acid; hydrogen ion. group with the pi electrons of the benzene ring in methylbenzene (toluene). hydrophilic /hÿ-drŏ-fil-ik/ Water attracting. See lyophilic. hyperfine structure /hÿ-per-fÿn/ See fine structure. hydrophobic /hÿ-drŏ-foh-bik/ Water repelling. See lyophobic. hypertonic solution A solution that has a higher osmotic pressure than some other hydroquinone /hÿ-droh-kwi-nohn, hÿ- solution. Compare hypotonic solution. droh-kwin-ohn/ See benzene-1,4-diol. hypo /hÿ-poh/ An old name for SODIUM hydrosol /hÿ-drŏ-sol, -sohl/ A colloid in THIOSULFATE(IV), especially when used in aqueous solution. photography. It was formerly known as sodium hyposulfite. hydroxide /hÿ-droks-ÿd, -id/ A compound containing the ion OH– or the hypobromous acid /hÿ-pŏ-broh-mŭs/ See group –OH. bromic(I) acid. hydroxonium ion /hÿ-droks-oh-nee-ŭm/ hypochlorous acid /hÿ-pŏ-klor-ŭs, -kloh- See hydrogen ion. rŭs/ See chloric(I) acid. hydroxybenzene /hÿ-droks-ee-ben-zeen, hypophosphorous acid /hÿ-pŏ-fos-fŏ- -ben-zeen/ See phenol. rŭs/ See phosphinic acid. hydroxybenzoate /hÿ-droks-ee-ben-zoh- hyposulfuric acid /hÿ-pŏ-sul-fyoor-ik/ ayt/ See salicylate. See dithionic acid. hydroxybenzoic acid /hÿ-droks-ee-ben- hyposulfurous acid /hÿ-per-sul-fyoor-ŭs/ zoh-ik/ See salicylic acid. See dithionous acid. hydroxyl group /hÿ-drox-ăl/ A group hypotonic solution A solution that has a (–OH) containing hydrogen and oxygen, lower osmotic pressure than some other characteristic of alcohols and phenols, and solution. Compare hypertonic solution.

140 I

Iceland spar A pure transparent mineral tion of aldehydes and ketones with pri- form of calcite (calcium carbonate, mary amines. For example, propanone CaCO3), noted for its property of birefrin- (acetone; CH3COCH3) with ethylamine gence (double refraction). (C2H6NH2): → CH3COCH3 + C2H6NH2 ideal gas (perfect gas) See gas laws; ki- (CH3)2C=N–C2H6 + H2O netic theory. The reaction is acid-catalyzed. When ammonia is used the imine contains the ideal-gas scale See absolute temperature. C=N–H group: → CH3COCH3 + NH3 (CH3)2C=N–H + ideal solution A hypothetical solution H2O that obeys RAOULT’S LAW. Most imines are unstable and can be detected only in solution unless R1, R2, or R3 ignis fatuus /ig-nis fach-û-ŭs/ (will-o’-the- are aryl groups. Intermediates in which an wisp) A light sometimes seen over marshy imine adds a proton to form a positive ion ground. It is caused by methane produced (e.g. R1R2C=NR3H+) are known as by rotting vegetation, which is ignited by iminium ions. the presence of small amounts of spontaneously flammable phosphine (PH3). iminium ion See imine. ignition temperature The temperature imino group /i-mee-noh, im-i-noh/ See to which a substance must be heated before imine. it will continue to burn (usually in air). iminourea /i-mee-noh-yû-ree-ă, im-ă- imide /im-ÿd, -id/ An organic compound noh- / See guanidine. containing the group –CO.NH.CO–, i.e. a –NH group attached to two carbonyl immiscible /i-miss-ă-băl/ Describing two groups. Simple imides have the general for- or more liquids that will not mix, such as mula R1.CO.NH.CO.R2, where R1 and R2 oil and water. After being shaken together are alkyl or aryl groups. The group is they form separate layers. known as the imido group, and it can form part of a ring in cyclic imides. indene /in-deen/ (C9H8) A colorless flammable hydrocarbon. It has a benzene ring imido group /i-mee-doh, im-i-doh/ See fused to a five-membered ring. imide. indicator A compound that reversibly imine /i-meen, im-in/ An organic com- changes color depending on the pH of the pound containing the group C=N–, in solution in which it is dissolved. The visual which there is a double bond between the observation of this change is therefore a carbon and the nitrogen. A general for- guide to the pH of the solution and it fol- mula for imines is R1R2C=N–R3, where lows that careful choice of indicators per- R1, R2, and R3 are hydrocarbon groups or mits a wide range of end points to be hydrogen. They can be made by the reac- detected in acid–base titrations.

141 indigo

Redox titrations require either specific ethene prisms and lenses are suitable for indicators, which detect one of the compo- use with infrared. Infrared radiation is pro- nents of the reaction (e.g. starch for iodine, duced by movement of charges on the mol- potassium thiocyanate for Fe3+) or true ecular scale; i.e. by vibrational or redox indicators in which the transition rotational motion of molecules. Of partic- potential of the indicator between oxidized ular importance in chemistry is the absorp- and reduced forms is important. The tran- tion spectrum of compounds in the sition potential of a redox indicator is anal- infrared region. Certain bonds between ogous to the transition pH in acid–base pairs of atoms (C–C, C=C, C=O, etc.) have systems. characteristic vibrational frequencies, Complexometric titrations require indi- which correspond to bands in the infrared cators that complex with metal ions and spectrum. Infrared spectra are thus used in change color between the free state and the finding the structures of new organic com- complex state. See also absorption indica- pounds. They are also used to ‘fingerprint’ tor. and thus identify known compounds. At shorter wavelengths, infrared absorption indigo (C16H10N2O2) A blue organic dye corresponds to transitions between rota- that occurs (as a glucoside) in plants of the tional energy levels, and can be used to find genus Indigofera. It is a derivative of in- the dimensions of molecules (by their mo- dole, and is now made synthetically. ment of inertia). /in-dee-ŭm/ A soft silvery metallic indium inhibitor A substance that slows down element belonging to group 13 of the peri- the rate of reaction. Hydrogen sulfide, hy- odic table. It is found in minute quantities, drogen cyanide, mercury salts, and arsenic primarily in zinc ores and is used in alloys, compounds readily inhibit heterogeneous in several electronic devices, and in electro- catalysts by adsorption. For example, ar- plating. senic compounds inhibit platinum catalysts Symbol: In; m.p. 155.17°C; b.p. in the oxidation of sulfur(IV) oxide to sul- 2080°C; r.d. 7.31 (25°C); p.n. 49; r.a.m. fur(VI) oxide. Inhibitors must not be con- 114.818. fused with negative catalysts; inhibitors do indole /in-dohl, -dol/ (benzpyrrole; not change the pathway of a reaction. C8H7N) A colorless solid organic compound, whose molecules consist of a ben- inner Describing a ring compound that is zene ring fused to a pyrrole ring. It occurs formed, or could be regarded as formed, by in coal tar and various plants, and is the one part of a molecule reacting with an- basis of indigo and of several plant hor- other. For example, a LACTAM is an inner mones. amide and a LACTONE is an inner ester. inductive effect /in-duk-tiv/ The effect in inorganic chemistry The branch of which substituent atoms or groups in an chemistry concerned with elements other organic compound can attract (–I) or push than carbon and with the preparation, away electrons (+I), forming polar bonds. properties, and reactions of their compounds. Certain simple carbon compounds inert gases See rare gases. are treated in inorganic chemistry, including the oxides, carbon disulfide, the infrared /in-fră-red/ (IR) ELECTROMAG- halides, hydrogen cyanide, and salts, such NETIC RADIATION with longer wavelengths as the cyanides, cyanates, carbonates, and than visible radiation. The wavelength hydrogencarbonates. range is approximately 0.7 µm to 1 mm. Many materials transparent to visible light insertion reaction A reaction in which an are opaque to infrared, including glass. atom or group is inserted between two Rock salt, quartz, germanium, or poly- other groups. See carbene.

142 invert sugar insoluble /in-sol-yŭ-băl/ Describing a and VAN DER WAALS FORCES, and the major compound that has a very low solubility (in component is the ELECTROSTATIC INTERAC- a specified solvent). TION OF DIPOLES. See hydrogen bond. instrumentation /in-strŭ-men-tay-shŏn/ internal energy Symbol: U The energy of The measurement of the conditions and the a system that is the total of the kinetic and control of processes within a chemical potential energies of its constituent parti- plant. The instruments can be classified cles (e.g. atoms and molecules). If the tem- into three groups: those for current infor- perature of a substance is raised, by mation using mercury thermometers, transferring energy to it, the internal en- weighing scales, and pressure gauges; those ergy increases (the particles move faster). for recording viscosity, fluid flow, pres- Similarly, work done on or by a system re- sure, and temperature; and those instru- sults in an increase or decrease in the inter- ments that control and maintain the nal energy. The relationship between heat, desired conditions including pH and the work, and internal energy is given by the flow of materials. first law of thermodynamics. Sometimes the internal energy of a system is loosely intercallation compound /in-terk-ă-lay- spoken of as ‘heat’ or ‘heat energy’. shŏn/ A compound that has a structure Strictly, this is incorrect; heat is the trans- based on layers and in which there are lay- fer of energy as a result of a temperature ers of a different character interleaved in difference. the basic structural units. For example, the micas phlogopite (KMg (OH) Si AlO ) 3 2 3 10 internal resistance Resistance of a source and muscovite (KAl (OH) Si AlO ) are 2 2 3 10 of electricity. In the case of a cell, when a formed by interleaving K+ ions replacing a current is supplied, the potential difference quarter of the silicon layers in talc and py- between the terminals is lower than the rophyllite respectively. See also lamellar e.m.f. The difference (i.e. e.m.f. – p.d.) is compound. proportional to the current supplied. The intermediate 1. A compound that re- internal resistance (r) is given by: quires further chemical treatment to pro- r = (E – V)/I duce a finished industrial product such as a where E is the e.m.f., V the potential dif- dye or pharmaceutical chemical. ference between the terminals, and I the 2. A transient chemical entity in a complex current. reaction. See also precursor. interstitial /in-ter-stish-ăl/ See defect. intermediate bond A form of covalent bond that also has an ionic or electrovalent interstitial compound A crystalline character. See polar bond. compound in which atoms of a non-metal (e.g. carbon, hydrogen, or boron) occupy intermediate bonding A form of cova- interstitial positions in the crystal lattice of lent bond that also has an ionic or elec- a metal (usually a transition metal). Inter- trovalent character. See polar bond. stitial compounds are often non-stoichiometric. Their physical properties are often intermolecular forces /in-ter-mŏ-lek-yŭ- similar to those of metals; e.g. they have a ler/ Forces of attraction between molecules metallic luster and are electrical conduc- rather than forces within the molecule tors. (chemical bonding). If these intermolecular forces are weak the material will be inversion /in-ver-shŏn/ A change from gaseous and as their strength progressively one optical isomer to the other. See Walden increases materials become progressively inversion. liquids and solids. The intermolecular forces are divided into H-bonding forces invert sugar See sucrose.

143 iodic acid iodic acid /ÿ-od-ik/ See iodic(V) acid. chlorine. Because of the larger size of the iodine ion and the consequent low lattice iodic(V) acid (iodic acid; HIO3) A color- energies, the iodides are generally more less deliquescent crystalline solid produced soluble than related bromides or chlorides. by the reaction of concentrated nitric acid As with the other halides, iodides of Ag(I), with iodine. Iodic(V) acid is a strong oxi- Cu(I), Hg(I), and Pb(II) are insoluble unless dizing agent. It will liberate iodine from so- complexing ions are present. lutions containing iodide ions and it reacts Iodine also forms a range of covalent vigorously with organic materials, often iodides with the metalloids and non-metal- producing flames. It dissociates extensively lic elements (this includes a vast range of in water and hence is a strong acid. organic iodides) but these are generally less thermodynamically stable and are more iodic(VII) acid (periodic acid; H5IO6) A readily hydrolyzed than chlorine or white crystalline solid made by low-tem- bromine analogs. perature electrolysis of concentrated Four oxides are known of which io- iodic(V) acid. It exists in a number of dine(V) oxide, I2O5, is the most important. forms, the most common of which is The other oxides, I2O4, I4O9, and I2O7 are paraiodic(VII) acid. Iodic(VII) acid is a much less stable and of uncertain structure. powerful oxidizing agent. It is a weak acid, Like chlorine (but not bromine) iodine which – by cautious heating under vacuum – – forms oxo-species based on IO , IO2 , – can be converted to dimesoiodic(VII) – – IO3 , and IO4 . The chemistry of the other acid (H4I2O9), and metaiodic(VII) acid oxo-species in solution is complex. Ele- (HIO ). All three will oxidize manganese 4 mental iodine reacts with alkalis in a simi- to manganate(VII) and this reaction can be lar way to bromine and chlorine. used to determine small amounts of man- The ionization potential of iodine is suf- ganese in steel. ficiently low for it to form a number of compounds in which it is electropositive. It iodide /ÿ-ŏ-dÿd, -did/ See halide. forms I+ cations, for example, by reaction of solid silver nitrate with iodine solution, iodine /ÿ-ŏ-dÿn, -deen/ A dark-violet volatile solid element belonging to the and such cations are sufficiently elec- halogens (group 17 of the periodic table). It trophilic to substitute aromatic com- occurs in seawater and is concentrated by pounds such as phenol. Iodine also exhibits various marine organisms in the form of io- the interesting property of forming solu- dides. Significant deposits also occur in the tions that are violet colored in non-donor form of iodates. The element is conve- type solvents, such as tetrachloromethane, niently prepared by the oxidation of io- but in donor solvents, such as ethanol or dioxan, there is a strong iodine–solvent in- dides in acid solution (using MnO2). Industrial methods similarly use oxidation teraction, which gives the solution a deep of iodides or reduction of iodates to iodides brown color. Even though iodine solutions by sulfur(IV) oxide (sulfur dioxide) fol- were commonly used as antiseptic agents, lowed by oxidation, depending on the the element is classified as toxic, and care source of the raw materials. Iodine and its should be taken to avoid eye intrusions or compounds are used in chemical synthesis, excessive skin contact. photography, pharmaceuticals, and dye- Symbol: I; m.p. 113.5°C; b.p. 184°C; stuffs manufacture. r.d. 4.93 (20°C); p.n. 53; r.a.m. Iodine has the lowest electronegativity 126.90447. of the stable halogens and consequently is the least reactive. It combines only slowly iodine monochloride /mon-ŏ-klor-ÿd, with hydrogen to form hydroiodic acid, -id, -kloh-rÿd, -rid/ (ICl) A dark red liquid HI. Iodine also combines directly with made by passing chlorine over iodine. It many electropositive elements, but does so has properties similar to those of its con- much more slowly than does bromine or stituent halogens. Iodine monochloride is

144 ionic radius used as a nonaqueous solvent and as an io- inert backbone material, such as dating agent in organic reactions. polyphenylethene, to which ionic groups are weakly attached. If the ions exchanged iodine number (iodine value) A number are positive, the resin is a cationic resin. An that gives a measure of the number of un- anionic resin exchanges negative ions. saturated bonds in an organic compound When all available ions have been ex- such as a fat or oil. It is found by measur- changed (e.g. sodium ions replacing cal- ing the amount of iodine in grams taken up cium ions) the material can be regenerated by 100 grams of the compound. by passing concentrated solutions (e.g. sodium chloride) through it. The calcium iodine(V) oxide (iodine pentoxide; I2O5) ions are then replaced by sodium ions. Ion- A white crystalline solid made by heating exchange techniques are used for a vast iodic(V) acid to a temperature of 200°C. It range of purification and analytical pur- is a very strong oxidizing agent. poses. Iodine oxide is the acid anhydride of For example, solutions with ions that iodic(V) acid, which is reformed when can be exchanged for OH– and H+ can be water is added to the oxide. Its main use is estimated by titrating the resulting solution in titration work, measuring traces of car- with an acid or a base. bon monoxide in the air. ionic bond /ÿ-on-ik/ See electrovalent iodine pentoxide /pen-toks-ÿd/ See io- bond. dine(V) oxide. ionic crystal A crystal composed of ions iodine trichloride /trÿ-klor-ÿd, -kloh-rÿd/ of two or more elements. The positive and See diiodine hexachloride. negative ions are arranged in definite patterns and are held together by electrostatic iodoethane /ÿ-od-oh-eth-ayn/ (ethyl io- attraction. Common examples are sodium dide; C2H5I) A colorless liquid alkyl halide chloride and cesium chloride. made by reaction of ethanol with iodine in the presence of red phosphorus. ionic product The product of concentrations: + – iodoform /ÿ-od-ŏ-form/ See triiodo- KW = [H ][OH ] methane. in water as a result of a small amount of self-ionization. iodoform reaction See triiodomethane. ionic radius A measure of the effective ra- iodomethane /ÿ-od-oh-meth-ayn/ (methyl dius of an ion in a compound. For an iso- iodide; CH3I) A liquid alkyl halide made lated ion, the concept is not very by reaction of methanol with iodine in the meaningful, since the ion is a nucleus sur- presence of red phosphorus. rounded by an ‘electron cloud’. Values of ionic radii can be assigned, however, based ion /ÿ-on, -ŏn/ An atom or molecule that on the distances between ions in crystals. has a negative or positive charge as a result Different methods exist for determining of losing or gaining one or more electrons. ionic radii and often different values are See electrolysis; ionization. quoted for the same ion. The two main methods are those of Goldschmidt and of ion exchange A process that takes place Pauling. The Goldschmidt radii are deter- in certain insoluble materials, which con- mined by substituting data from one com- tain ions capable of exchanging with ions pound to another, to produce a set of ionic in the surrounding medium. Zeolites, the radii for different ions. The Pauling radii first ion exchange materials, were used for are assigned by a more theoretical treat- water softening. These have largely been ment for apportioning the distance be- replaced by synthetic resins made of an tween an anion and a cation.

145 ionic strength ionic strength For an ionic solution a stance, and is usually stated in kilojoules quantity can be introduced which empha- per mole (kJ mol–1). sizes the charges of the ions present: In chemistry, the terms ‘second’, ‘third’, ½Σ 2 I = imiz i etc., ionization potentials are usually used where m is the molality and z the ionic for the formation of doubly, triply, etc., charge. The summation is continued over charged ions. However, in spectroscopy all the different ions in the solution, i. and physics, they are often used with a different meaning. The second ionization po- ionization /ÿ-ŏ-ni-zay-shŏn/ The process tential is the energy to remove the second of producing ions. There are several ways least strongly bound electron in forming a in which ions may be formed from atoms singly charge ion. For lithium (ls22s1) it or molecules. In certain chemical reactions would refer to removal of a 1s electron to ionization occurs by transfer of electrons; produce an excited ion with the configura- 1 1 for example, sodium atoms and chlorine tion 1s 2s . Note also that ionization po- atoms react to form sodium chloride, tentials are now stated as energies. which consists of sodium ions (Na+) and Originally they were the potential through chloride ions (Cl–). Certain molecules can which an electron had to be accelerated to ionize in solution; acids, for example, form cause ionization by electron impact: – → 2+ – hydrogen ions as in the reaction M + e M + 2e → + 2– They were thus stated in volts. H2SO4 2H + SO4 The ‘driving force’ for ionization in a solution is solvation of the ions by mol- ionizing radiation Radiation of sufficiently high energy to cause IONIZATION. It ecules of the solvent. H+, for example, is may be short-wavelength electromagnetic solvated as a hydroxonium (hydronium) radiation (ultraviolet, x-rays, or gamma ion, H O+. 3 rays) or streams of particles. Ions can also be produced by ionizing radiation; i.e. by the impact of particles or ion pair A positive ion and a negative ion photons with sufficient energy to break up in close proximity in solution, held by the molecules or detach electrons from atoms: attractive force between their charges. See → + – A A + e . Negative ions can be formed Debye–Hückel theory; electrolysis. by capture of electrons by atoms or mol- – → – ecules: A + e A . IP See ionization potential. ionization energy See ionization poten- IR See infrared. tial. iridium /i-rid-ee-ŭm/ A white transition ionization potential (IP; Symbol: I) The metal that is highly resistant to corrosion. energy required to remove an electron It is used in electrical contacts, in spark from an atom (or molecule or group) in the plugs, and in jewelry. gas phase, i.e. the energy required for the Symbol: Ir; m.p. 2410°C; b.p. 4130°C; process: r.d. 22.56 (17°C); p.n. 77; r.a.m. 192.217. M → M+ + e– It gives a measure of the ability of metals to iron /ÿ-ern/ A transition element occur- form positive ions. The second ionization ring in many ores, especially the oxides potential is the energy required to remove (haematite and magnetite) and carbonate. two electrons and form a doubly charged It is extracted in a blast furnace using coke, ion: limestone, and hot air. The coke and air M → M2+ + e– form carbon monoxide, which then re- Ionization potentials stated in this way duces the iron ore to iron. The limestone are positive; often they are given in elec- removes acidic impurities and forms a tronvolts. Ionization energy is the energy layer of slag above the molten iron at the required to ionize one mole of the sub- base of the furnace. Steel is formed by re-

146 iron(III) sulfate ducing the carbon content to between 0.1 sence of air. It is only really stable at high and 1.5%. Iron is used as a catalyst in the temperatures and disproportionates slowly Haber process for ammonia production. It on cooling to give iron(III) oxide and iron. corrodes in air and moisture to hydrated Iron(II) oxide can be reduced by heating in iron(III) oxide (rust). a stream of hydrogen. When exposed to The most stable oxidation state is +3, air, it is oxidized to iron(III) oxide. It is a which is yellow, but +2 (green) and +6 (eas- basic oxide, dissolving readily in dilute ily reduced) also exist. Solutions of iron(II) acids to form iron(II) salt solutions. If ions give a green precipitate with sodium heated to a high temperature in an inert at- hydroxide solution, whereas iron(III) ions mosphere, iron(II) oxide disproportionates give a brown precipitate. The concentra- to give iron and triiron tetroxide. tion of iron(II) ions can be estimated in acid solution by titration with standard iron(III) oxide (ferric oxide; Fe2O3) A potassium manganate(VII) solution. rusty-brown solid prepared by the action Iron(III) ions must first be reduced to of heat on iron(III) hydroxide or iron(II) iron(II) ions with sulfur(IV) oxide (sulfur sulfate. It occurs in nature as the mineral dioxide). hematite. Industrially it is obtained by Symbol: Fe; m.p. 1535°C; b.p. 2750°C; roasting iron pyrites. Iron(III) oxide dis- r.d. 7.874 (20°C); p.n. 26; r.a.m. 55.845. solves in dilute acids to produce solutions of iron(III) salts. It is stable at red heat, de- ° iron(II) chloride (ferrous chloride; FeCl2) composes around 1300 C to give triiron A compound prepared by passing dry hy- tetroxide, and can be reduced to iron by drogen chloride gas over heated iron. hydrogen at 1000°C. Iron(III) oxide is not White feathery anhydrous crystals are pro- ionic in character but has a structure simi- duced. Hydrated iron(II) chloride lar to that of aluminum(III) oxide. (FeCl2.6H2O) is prepared by reacting excess iron with dilute or concentrated hy- iron(II) sulfate (ferrous sulfate; green vit- drochloric acid. Green crystals of the riol; FeSO4.7H2O) A compound that oc- hexahydrate are obtained on crystalliza- curs in nature as the mineral melanterite tion from solution. Iron(II) chloride is (or copperas). It is made industrially from readily soluble in water, producing an iron pyrites. In the laboratory iron(II) sul- acidic solution due to salt hydrolysis. fate is prepared by dissolving excess iron in dilute sulfuric acid. On crystallization, iron(III) chloride (ferric chloride; FeCl3) green crystals of the heptahydrate are ob- A compound prepared in the anhydrous tained. Careful heating of the hydrated salt state as dark red crystals by passing dry yields anhydrous iron(II) sulfate; on fur- chlorine over heated iron. The product ther heating the sulfate decomposes to give sublimes and is collected in a cooled re- iron(III) oxide, sulfur(IV) oxide, and sul- ceiver. The hydrated salt (FeCl3.6H2O) is fur(VI) oxide. The hydrated crystals oxi- prepared by adding excess iron(III) oxide dize easily on exposure to air owing to the to concentrated hydrochloric acid. On formation of basic iron(III) sulfate. A crystallization yellow-brown crystals of the freshly prepared solution of iron(II) sulfate hexahydrate are formed. Iron(III) chloride absorbs nitrogen(II) oxide (brown-ring is very soluble in water and undergoes salt test). hydrolysis. At temperatures below 400°C Iron(II) sulfate crystals are isomor- the anhydrous salt exists as a dimer, phous with the sulfates of zinc, magne- Fe2Cl6. sium, nickel, and cobalt. iron(II) oxide (ferrous oxide; FeO) A iron(III) sulfate (ferric sulfate; Fe2(SO4)3) black powder formed by the careful reduc- A compound prepared in the hydrated tion of iron(III) oxide using either carbon state by the oxidation of iron(II) sulfate monoxide or hydrogen. It can also be pre- dissolved in dilute sulfuric acid, using an pared by heating iron(II) oxalate in the ab- oxidizing agent, such as hydrogen peroxide

147 irreversible change or concentrated nitric acid. On crystalliza- test for the primary amine group. The sus- tion, the solution deposits a white mass of pected primary amine is warmed with the nonahydrate (Fe2(SO4)3.9H2O). The trichloromethane in an alcoholic solution anhydrous salt can be prepared by gently of potassium hydroxide. The resulting iso- heating the hydrated salt. Iron(III) sulfate cyanide (RNC) has a characteristic smell of decomposes on heating to give iron(III) bad onions (and is very toxic): → oxide and sulfur(VI) oxide. It forms alums CHCl3 + 3KOH + RNH2 RNC + with the sulfates of the alkali metals. 3KCl + 3H2O irreversible change /i-ri-ver-să-băl/ See isoelectronic /ÿ-soh-i-lek-tron-ik/ De- reversible change. scribing compounds that have the same number of electrons. For example, carbon irreversible reaction A reaction in which monoxide (CO) and nitrogen (N2) are iso- conversion to products is complete; i.e. electronic. there is little or no back reaction. isoleucine /ÿ-sŏ-loo-seen, -loo-sin/ See isobars /ÿ-sŏ-barz/ 1. Two or more nu- amino acids. clides that have the same nucleon numbers but different proton numbers. isomer /ÿ-sŏ-mer/ See isomerism. 2. Lines joining points of equal pressure. isomerism /ÿ-som-ĕ-riz-ăm/ The existence isocyanide /ÿ-sŏ-sÿ-ă-nÿd/ See isonitrile. of two or more chemical compounds with the same molecular formulae but different isocyanide test (carbylamine reaction) A structural formulae or different spatial

CH3 H2 C CH3 C H C C C C H3 H2 H3 H3

butane methylpropane (n-butane) (isobutane) Isomer: isomers differing in carbon skeleton

C C C H C H3 3 H3 OH

dimethyl ether ethanol

Isomer: isomers differing in the nature of the functional group

H2 C OH C H C C C C H3 H2 H3 H3

propan-1-ol propan-2-ol (n-propanol) (isopropanol)

Isomer: isomers differing in the position of a functional group

148 isomerism

H2 H C C C H3C C C CH3

CH3

propan-1-yne propan-2-yne

Isomer: isomers differing in the position of a multiple bond arrangements of atoms. The different merism, the isomers differ because of the forms are known as isomers. For example, position of a functional group in the mole- the compound C4H10 may be butane cule. For example, the primary alcohol (CH3CH2CH2CH3, with a straight chain propan-1-ol (CH3CH2CH2OH) and the of carbon atoms) or 2-methyl propane secondary alcohol propan-2-ol (CH3CH(CH3)CH3, with a branched (CH3CH(OH)CH3) are isomers; both have chain). the molecular formula C3H7OH. Structural isomerism is the type of iso- Structural isomerism also occurs in in- merism in which the structural formulae of organic chemistry. A particular case is the compounds differ. There are two main found in complexes in which a ligand may forms. In one the isomers are different coordinate to a metal ion in two ways. For types of compound. An example of this is example, NO2 can coordinate through N the compounds ethanol (C2H5OH) and (the nitro ligand) or through O (the nitrido methoxymethane (dimethyl ether, CH3O- ligand). Such ligands are said to be am- CH3), both having the molecular formula bidentate. Complexes that differ only in C2H6O but quite different functional the way in which the ligand coordinates are groups. In the other type of structural iso- said to show linkage isomerism.

Cl Cl Cl H

CC CC

H H H Cl

cis-dichloroethene trans-dichloroethene

Isomer: cis-trans isomerism in an alkene

CH3 OH CH3

NC NC

C2H6 C2H6 OH

E-methylethylketone oxime Z-methylethylketone oxime

Isomer: E–Z isomerism in an oxime

H O H H O C2H5

C C C C

C2H5 C H C2H5 2 5 H cis-diethyl epoxide trans-diethyl epoxide

Isomer: cis–trans isomerism in a ring compound

149 isomorphism

Y X

Y M X Y M Y

X X

cis-isomer trans-isomer

Isomerism Stereoisomerism occurs when two com- to each atom may be on the same side of pounds with the same molecular formulae the bond (the cis- or syn-isomer) or oppo- and the same groups differ only in the site sides (the trans- or anti-isomer). Cis- arrangement of the groups in space. There trans isomerism also occurs in are two types of stereoisomerism. square-planar complexes of the type Cis–trans (or syn–anti) isomerism oc- MX2Y2, where M is a metal ion and X and curs when there is restricted rotation about Y are different ligands. If the X ligands are a bond between two atoms (e.g. a double adjacent the isomer is a cis-isomer; if they bond or a bond in a ring). Groups attached are opposite, it is a trans-isomer. This type

Y Y

Y X

X M X X M Y

Y Y

Y Y trans-isomer cis-isomer

X X

X Y

X M Y X M Y

Y Y

Y X fac-isomer mer-isomer

Isomerism

150 isotopes of isomerism can also occur in octahedral rium with its surroundings. For example, a complexes of the type MX2Y4. Cis–trans cylinder of gas in contact with a constant- isomerism was formerly called geometrical temperature box may be compressed isomerism. slowly by a piston. The work done appears Octahedral complexes of the type as energy, which flows into the reservoir to MX3Y3 show a different type of stereoiso- keep the gas at the same temperature. merism. If the three X ligands are in a plane Isothermal changes are contrasted with that includes the M ion (with the three Y adiabatic changes, in which no energy en- ligands in a plane at right angles), then the ters or leaves the system, and the tempera- structure is called the mer-isomer (‘mer’ ture changes. In practice no process is stands for meridional). If the three X (and perfectly isothermal and none is perfectly Y) ligands are all on a face of the octahe- adiabatic, although some can approximate dron, the structure is the fac-isomer (‘fac’ in behavior to one of these ideals. stands for facial). See also E–Z convention Optical isomerism occurs when the isotones /ÿ-sŏ-tohnz/ Two or more nu- compound has no plane of symmetry and clides that have the same neutron numbers can exist in left- and right-handed forms but different proton numbers. that are mirror images of each other. Such molecules always contain a CHIRAL ELE- isotonic /ÿ-sŏ-tonn-ik/ Describing solu- MENT. Molecules that are mirror images of tions that have the same osmotic pressure. each other are more properly called enan- tiomers. Stereoisomers that are not mirror isotopes /ÿ-sŏ-tohps/ Two or more species images are called diastereoisomers. For ex- of the same element differing in their mass ample, ANOMERS are diastereoisomers. See numbers because of differing numbers of also optical activity. neutrons in their nuclei. The nuclei must have the same number of protons (an ele- isomorphism /ÿ-sŏ-mor-fiz-ăm/ The exis- ment is characterized by its proton num- tence of compounds with the same crystal ber). Isotopes of the same element have structure. very similar properties because they have the same electron configuration, but differ isomorphism, law of See Mitscherlich’s slightly in their physical properties. An un- law. stable isotope is termed a radioactive iso- isonitrile /ÿ-sŏ-nÿ-trăl, -tril, -trÿl/ (isotope or radioisotope cyanide) An organic compound of the for- Isotopes of elements are useful in chem- mula R–NC. istry for studies of the mechanisms of chemical reactions. A standard technique is isoprene /ÿ-sŏ-preen/ See methylbuta-1,3- to label one of the atoms in a molecule by diene. using an isotope of the element. It is then possible to trace the way in which this isopropanol /ÿ-sŏ-proh-pă-nol, -nohl/ atom behaves throughout the course of the Propan-2-ol. See propanol. reaction. For example, in the esterification reaction: ′ ˆ ′ isotactic polymer See polymerization. ROH + R COOH H2O + R COOR it is possible to find which bonds are bro- isotherm /ÿ-sŏ-therm/ A line on a chart or ken by using a labeled oxygen atom. If the graph joining points of equal temperature. reaction is performed using 18O in the al- See also isothermal change. cohol it is found that this nuclide appears in the ester, showing that the C–OH bond isothermal change /ÿ-sŏ-therm-ăl/ A of the acid is broken in the reaction. In la- process that takes place at a constant tem- beling, radioisotopes are detected by coun- perature. Throughout an isothermal ters; stable isotopes can also be used, and process, the system is in thermal equilib- detected by a mass spectrum.

151 isotope separation

Isotopes are also used in kinetic studies. uranium using the gas uranium hexafluo- For example, if the bond between two ride), distillation (which was used to pro- atoms X–Y is broken in the rate-determin- duce heavy water), electrolysis (also used ing step, and Y is replaced by a heavier iso- for heavy water), and the use of cen- tope of the element, Y*, then the reaction trifuges. Laser separation may also be em- rate will be slightly lower with the Y* pre- ployed, with excitation of one isotope sent. This kinetic isotope effect is particu- occurring, followed by its separation using larly noticeable with hydrogen and an electromagnetic field. deuterium compounds, because of the large relative difference in mass. isotopic mass /ÿ-sŏ-top-ik/ (isotopic isotope separation /ÿ-sŏ-tohp/ The sepa- weight) The mass number of a given iso- ration of different isotopes of a chemical el- tope of an element. ement, making use of differences in the physical properties of these isotopes. For isotopic number The difference between small-scale isotope separation a MASS SPEC- the number of neutrons in an atom and the TROMETER is frequently used. For large- number of protons. scale isotope separation the methods used include diffusion in the gas phase (used for isotopic weight See isotopic mass.

152 J

jeweler’s rouge Iron(III) oxide (Fe2O3), and work, equal to the work done when used as a mild abrasive. the point of application of a force of one newton moves one meter in the direction of joliotium /zhoh-lee-oh-shee-ŭm/ Symbol: action of the force. 1 J = 1 N m. The joule Jl A name formerly suggested for element- is the unit of all forms of energy. The unit 105 (dubnium). See element. is named for the British physicist James Prescott Joule (1818–89). joule /jool/ Symbol: J The SI unit of energy

153 K

kainite /kay-ă-nÿt, kÿ-nÿt/ A mineral form horn, and hooves. The keratins contain of hydrated crystalline magnesium sulfate polypeptide chains linked by disulfide (MgSO4) containing also some potassium bonds between cystein amino acids. chloride. It is used as a fertilizer and source of potassium compounds. kerosene /ke-rŏ-seen, ke-rŏ-seen/ See petroleum. kaolin /kay-ŏ-lin/ See china clay. ketal /kee-t’l/ A type of organic compound kaolinite /kay-ŏ-li-nÿt/ A hydrated alumi- formed by addition of an alcohol to a ke- nosilicate mineral, Al2(OH)4Si2O5, the tone. Addition of one molecule gives a major constituent of kaolin. It is formed by hemiketal; two molecules give a full ketal. the weathering of FELDSPARS from granites. See acetal. katal /kay-t’l/ Symbol: kat The SI derived ketene /kee-teen/ (keten) A member of a unit of catalytic activity, equal to the group of organic compounds, general for- amount of substance in moles that can be mula R2C:CO, where R is hydrogen or an catalyzed per second. 1 kat = l mol s–1. organic radical. The simplest member is the colorless gas ketene, CH2:CO; the katharometer /kath-ă-rom-ĕ-ter/ See gas other ketenes are colored because of the chromatography. presence of the double bonds. Ketenes are unstable and react with other unsaturated Kekulé structure /kay-koo-lay/ A struc- compounds to give cyclic compounds. ture of BENZENE in which there is a hexagonal ring with alternate double and single keto–enol tautomerism /kee-toh ee-nol/ bonds. Two possible Kekulé structures An equilibrium between two isomers in contribute to the RESONANCE hybrid of ben- which one isomer is a ketone (the keto zene. The structure is named for the Ger- form) and the other an enol. The equilib- man chemist Friedrich Augus Kekulé von rium is by transfer of a hydrogen atom be- Stradonitz (1829–96). tween the oxygen atom of the carbonyl group and an adjacent carbon atom. kelvin Symbol: K The SI base unit of thermodynamic temperature. It is defined as keto form /kee-toh/ See keto–enol tau- the fraction 1/273.16 of the thermody- tomerism. namic temperature of the triple point of water. Zero kelvin (0 K) is absolute zero. ketohexose /kee-toh-heks-ohs/ A ketose One kelvin is the same as one degree on the SUGAR with six carbon atoms. Celsius scale of temperature. The unit is named for the British theoretical and ex- ketone /kee-tohn/ A type of organic com- perimental physicist William Thompson, pound with the general formula RCOR, Baron Kelvin (1824–1907). having two alkyl or aryl groups bound to a carbonyl group. They are made by oxidiz- keratin /ke-ră-tin/ Any of a class of fi- ing secondary alcohols (just as ALDEHYDES brous proteins found in hair, feathers, are made from primary alcohols). Simple

154 kinetic theory

R kilo- Symbol: k A prefix denoting 103. For 3 O example, 1 kilometer (km) = 10 meters C (m). R kilocalorie /kil-ŏ-kal-ŏ-ree/ See calorie. Ketone kilogram /kil-ŏ-gram/ (kilogramme; Sym- bol: kg) The SI base unit of mass, equal to examples are propanone (acetone, the mass of the international prototype of CH3COCH3) and butanone (methyl ethyl the kilogram, which is a piece of plat- ketone, CH3COC2H5). inum–iridium kept at Sèvres in France. The chemical reactions of ketones are similar in many ways to those of aldehydes. kilogramme /kil-ŏ-gram/ An alternative The carbonyl group is polarized, with pos- spelling of kilogram. itive charge on the carbon and negative charge on the oxygen. Thus nucleophilic kilowatt-hour /kil-ŏ-wot/ Symbol: kWh addition can occur at the carbonyl group. A unit of energy, usually electrical, equal to Ketones thus: the energy transferred by one kilowatt of 1. Undergo addition reactions with hydro- power in one hour. It has a value of 3.6 × gen cyanide and hydrogensulfite ions. 106 joules. 2. Undergo condensation reactions with hydroxylamine, hydrazine, and their de- kinetic energy /ki-net-ik/ See energy. rivatives. 3. Are reduced to (secondary) alcohols. kinetic isotope effect See isotopes. They are not, however, easily oxidized. Strong oxidizing agents give a mixture kinetics /ki-net-iks/ A branch of physical of carboxylic acids. They do not react chemistry concerned with the study of with Fehling’s solution or Tollen’s rates of chemical reactions and the effect of reagent, and do not easily polymerize. physical conditions that influence the rate of reaction, e.g. temperature, light, concen- ketopentose /kee-toh-pen-tohs/ A ketose tration, etc. The measurement of these SUGAR with five carbon atoms. rates under different conditions gives information on the mechanism of the reaction; ketose /kee-tohs/ A SUGAR containing a i.e. on the sequence of processes by which keto- (=CO) or potential keto- group. reactants are converted into products. kieselguhr /kee-zĕl-goor/ See diatomite. kinetic theory A theory explaining physical properties in terms of the motion of killed spirits Zinc(II) chloride solution particles. The kinetic theory of gases as- used as a flux for solder, so called because sumes that the molecules or atoms of a gas it is made by adding zinc to hydrochloric are in continuous random motion and the acid (‘spirits of salt’). pressure (p) exerted on the walls of a con-

H OH O C C ˆ C C H H enol form keto form

Keto-enol tautomerism

155 Kipps apparatus taining vessel arises from the bombard- Kjeldahl’s method /kyel-dahlz/ A ment by these fast moving particles. When method used for the determination of ni- the temperature is raised the speeds in- trogen in organic compounds. The nitroge- crease; so consequently does the pressure. nous substance is converted to ammonium If more particles are introduced or the vol- sulfate by boiling with concentrated sulfu- ume is reduced there are more particles to ric acid (often with a catalyst such as bombard unit area of the walls and the CuSO4) in a specially designed long-necked pressure also increases. When a particle Kjeldahl flask. The mixture is then made collides with the wall it experiences a rate alkaline and the ammonia distilled off into of change of momentum, which is propor- standard acid for measurement by titra- tional to the force exerted. For a large tion. The method is named for the Danish number of particles this provides a steady chemist Johan Gustav Christoffer Thor- pressure on the wall. sager Kjeldahl (1849–1900). Additional assumptions are: 1. The particles behave as if they are hard Kolbe electrolysis /kol-bee/ The electrol- smooth perfectly elastic points. ysis of sodium salts of carboxylic acids to 2. They do not exert any appreciable force prepare alkanes. The alkane is produced at on each other except during collisions. the anode after discharge of the carboxy- 3. The volume occupied by the particles late anion and decomposition of the radi- themselves is a negligible fraction of the cal: RCOO– → RCOO• + e– volume of the gas. → 4. The duration of each collision is negligi- RCOO• R• + CO2 R• + RCOO• → R – R + CO ble compared with the time between col- 2 and lisions. 2R• → R – R By considering the change in momen- As the reaction is a coupling reaction, tum on impact with the walls it can be only alkanes with an even number of car- shown that bon atoms in the chain can be prepared in p = ρc2/3 this way. The process is named for the Ger- where ρ is the density of the gas and c is the man chemist Adolph Wilhelm Hermann root-mean-square speed of the molecules. Kolbe (1818–84). The mean-square speed of the molecules is proportional to the absolute temperature: /krol/ A method of obtain- 2 Kroll process Nmc = RT ing certain metals by reducing the metal See also degrees of freedom. chloride with magnesium. Titanium can be obtained in this way: Kipps apparatus /kips/ An apparatus for → TiCl4 + 2Mg 2MgCl2 + Ti the production of a gas from the reaction The process is named for the Luxem- of a liquid on a solid. It consists of three bourg metallurgist William Justin Kroll globes, the upper globe being connected (1889–1873). via a wide tube to the lower globe. The upper globe is the liquid reservoir. The krypton /krip-ton/ A colorless odorless middle globe contains the solid and also monatomic element of the rare-gas group, has a tap at which the gas may be drawn known to form unstable compounds with off. When the gas is drawn off the liquid fluorine. It occurs in minute quantities rises from the lower globe to enter the mid- (0.001% by volume) in air. Krypton is used dle globe and reacts with the solid, thereby in fluorescent lights. Symbol: Kr; m.p. releasing more gas. When turned off the –156.55°C; b.p. –152.3°C; d. 3.749 (0°C) gas released forces the liquid back down kg m–3; p.n. 36; r.a.m. 83.80. into the lower globe and up into the reservoir, thus stopping the reaction. The appa- kurchatovium /ker-chă-toh-vee-ŭm/ Sym- ratus is named for the Dutch chemist bol: Ku A former name for element-104 Petrus Jacobus Kipps (1808–64). (rutherfordium). See element.

156 L

label A stable or radioactive nuclide used lactim /lak-tim/ See lactam. to investigate some process, such as a chemical reaction. See isotopes. lactone /lak-tohn/ A type of organic compound containing the group –O.CO– as labile /lay-băl/ Describing a complex with part of a ring in the molecule. A lactone ligands that can easily be replaced by more can be regarded as formed from a com- strongly bonded ligands. pound with an alcohol (–OH) group on one end of the chain and a carboxylic acid lactam /lak-tam/ A type of organic com- (–COOH) group on the other. The lactone pound containing the –NH.CO– group as then results from reaction of the –OH part of a ring in the molecule. Lactams can group with the –COOH group; i.e. it is an be regarded as formed from a straight- internal ester. chain compound that has an amine group (–NH2) at one end of the molecule and a carboxylic acid group (–COOH) at the C O other; i.e. from an amino acid. The reac- C O tion of the amine group with the carboxylic acid group, with elimination of water, C leads to the cyclic lactam, which is thus an internal amide. Lactams may exist in an alternate tautomeric form in which the hy- Lactone drogen atom has migrated from the N onto the O of the carbonyl group. This, the lactim form, contains the group –N=C(OH)–. lactose /lak-tohs/ (milk sugar; C12H22O11) A sugar found in milk. It is a disaccharide composed of glucose and galactose units.

H Ladenburg benzene /lan-dĕn-berg/ A structure once suggested for BENZENE in which the six carbon atoms are at the cor- C N ners of a triangular prism with each carbon C O atom bonded to a hydrogen atom. It is C named for the German chemist Albert Ladenburg (1842–1911). The actual compound with this structure, known as prismane, was synthesized in 1973. Lactam lake A pigment made by combining an or- lactate /lak-tayt/ A salt or ester of lactic ganic dyestuff with an inorganic com- acid. pound (e.g. aluminum oxide). lactic acid /lak-tik/ See 2-hydroxy- lamellar compound /lă-mel-er/ A com- propanoic acid. pound with a crystal structure composed

157 lamp black of thin plates or layers. Silicates form many extraction methods have been specially de- compounds with distinct layers. Typical veloped for the lanthanoids. examples are talc (Mg3(OH)2Si4O10) and pyrophyllite (Al2(OH)2Si4O10). See also in- lanthanons /lan-thă-nŭs/ See lanthanoids. tercallation compound. lanthanum /lan-thă-nŭm/ A soft ductile lamp black A black pigment; a finely di- malleable silvery metallic element that is vided form of carbon formed by incom- the first member of the lanthanoid series. It plete combustion of an organic compound. is found associated with other lanthanoids in many minerals, including monazite and Langmuir isotherm /lang-myoor/ An bastnaesite. Lanthanum is used in several equation used to describe the adsorption of alloys (especially for lighter flints), as a cat- a gas onto a plane surface at a fixed tem- alyst, and in making optical glass. ° ° perature. It can be written in the form: Symbol: La; m.p. 921 C; b.p. 3457 C; ° θ = bp/ (1 + bp), r.d. 6.145 (25 C); p.n. 57; r.a.m. where θ is the fraction of the surface cov- 138.9055. ered by the gas, p is the gas pressure, and b is a constant known as the adsorption co- lapis lazuli /lap-is laz-yŭ-lÿ, -lee/ A deep efficient, which is the equilibrium constant blue mineral consisting of sodium alu- for the adsorption process. The equation minum sulfate with some sulfur, widely was derived by the American chemist Irv- used for ornaments and as a semiprecious ing Langmuir (1881–1957) in 1916 using gemstone. It was the original source of the pigment ultramarine. the kinetic theory of gases. laser /lay-zer/ An acronym for Light Am- lanolin /lan-ŏ-lin/ A yellowish viscous plification by Stimulated Emission of Radi- substance obtained from wool fat. It con- ation. A laser device produces high- tains cholesterol and terpene compounds, intensity, monochromatic, coherent beams and is used in cosmetics, in ointments, and of light. In the laser process the molecules in treating leather. of a sample (such as ruby doped with Cr3+ ions) are promoted to an excited state. As /lan-thă-nÿdz, -nidz/ See lan- lanthanides the sample is in a cavity between two re- thanoids. flective surfaces, when a molecule emits spontaneously, the photon so generated lanthanoids /lan-thă-noidz/ (lanthanides; ricochets backwards and forwards. In this lanthanons) A group of elements whose way other molecules are stimulated to emit electronic configurations display back fill- photons of the same energy. If one of the ing of the 4f-level. There is a maximum of reflective surfaces is partially transmitting 14 electrons in an f-orbital. The element this radiation can be tapped. lanthanum itself has no f-electrons (La 1 2 [Xe]5d 6s ) and is thus strictly not a lan- laser spectroscopy Spectroscopy that thanoid, but it is included by convention, uses lasers as a radiation source. Laser thus giving a closely related series of 15 el- spectroscopy is particularly important ements. Excluding lanthanum, the ele- when an intense beam of monochromatic x 2 ments all have 4f 6s configurations but radiation is needed, as in the RAMAN EF- gadolinium and lutecium have an addi- FECT. Pulsed-laser techniques are also used tional 5d1 electron. (see femtochemistry). The characteristic oxidation state is M3+ and the great similarity in the size of latent heat /lay-tĕnt/ The heat evolved or the ions leads to a very close similarity of absorbed when a substance changes its chemical properties and hence to great dif- physical state, e.g. the latent heat of fusion ficulties of separation using conventional is the heat absorbed when a substance methods. Chromatographic and solvent- changes from a solid to a liquid.

158 lead laterite /lat-ĕ-rÿt/ A red fine-grained type law of reciprocal proportions See of clay formed in tropical climates by the equivalent proportions, law of. weathering of igneous rocks. Its color comes from the presence of iron(III) hy- lawrencium /lor-en-see-ŭm/ A radioactive droxide. transuranic element of the actinoid series, not found naturally on Earth. Several very lattice A regular three-dimensional short-lived isotopes have been synthesized arrangement of points. A lattice is used to by bombarding 252Cf with boron nuclei or describe the positions of the particles 249Bk with 18O nuclei. (atoms, ions, or molecules) in a crystalline Symbol: Lr; p.n. 103; most stable iso- solid. The lattice structure can be exam- tope 262Lr (half-life 261 minutes). ined by x-ray diffraction techniques. laws of chemical combination See lattice energy The energy released when chemical combination; laws of. ions of opposite charge are brought together from infinity to form one mole of a lazurite /laz-yŭ-rÿt/ An uncommon typi- given crystal. The lattice energy is a mea- cally azure blue mineral consisting of a sil- sure of the stability of a solid ionic sub- icate of sodium, calcium, and aluminum stance, with respect to ions in the gas. See with some sulfur. It and its parent rock, also Born–Haber cycle. lapis lazuli, are widely used for ornaments and as semiprecious gemstones. Lazurite laughing gas See dinitrogen oxide. was the original source of the pigment ultramarine. lauric acid /lô-rik/ See dodecanoic acid. leaching The washing out of a soluble law of conservation of energy See con- material from an insoluble solid using a servation of energy; law of. solvent. This is often carried out in batch tanks or by dispersing the crushed solid in law of conservation of mass See con- a liquid. servation of mass; law of. lead /led/ A dense, dull, gray, soft metallic law of constant composition See con- element; the fifth member of group 14 (for- stant proportions; law of. merly VA) of the periodic table and the end law of constant heat summation See product of radioactive decay series. It oc- Hess’s law. curs in small quantities in a wide variety of minerals but only a few are economically law of constant proportions See con- important. The most important one is stant proportions; law of. galena (PbS), found in Australia, Mexico, the USA, and Canada. Other minerals are law of definite proportions See definite anglesite (PbSO4), litharge (PbO), and proportions; law of. cerussite (PbCO3). Galena is often associated with zinc law of equivalent proportions See ores and the smelting operations of both equivalent proportions, law of. lead and zinc industries are closely integrated. The ore is concentrated by froth law of isomorphism See Mitscherlich’s flotation and the concentrate roasted then law. reduced, → 2PbS + 3O2 2PbO + 2SO2 → law of mass action See mass action; law PbS + 2O2 PbSO4 of. 2PbO + 2C → 2Pb + 2CO → 2PbO + PbS 3Pb + SO2 → law of octaves See Newlands’ law. PbSO4 + 2C Pb + 2CO + SO2 159 lead(II) acetate

Silver is often recovered in economic quan- recharge the accumulator, charge is passed tities from crude lead. through it in the opposite direction to the The outer s2p2 configurations of tin and direction of current supply. This reverses lead give rise to similar properties for the the cell reactions and increases the relative two metals. There is however a much density of the electrolyte (c. 1.25 for a fully greater predominance of the divalent state charged accumulator). for lead. Both oxides are amphoteric, The electrolyte contains hydrogen ions + 2– lead(II) oxide (PbO) leading to plumbites (H ) and sulfate ions (SO4 ). During dis- + and lead(IV) oxide (PbO2) to plumbates on charge, H ions react with the lead(IV) dissolution in alkalis. Lead also forms oxide to give lead(II) oxide and water + – → mixed oxides Pb2O3 (a yellow solid, better PbO2 + 2H + 2e PbO + H2O written as Pb(II)Pb(IV)O3) and Pb3O4 (red This reaction takes electrons from the lead, Pb2(II)Pb(IV)O4). Both metals have plate, causing the positive charge. There is low melting points and neither is attacked a further reaction to yield soft lead sulfate: 2– + → by dilute acids; they differ however in their PbO + SO4 + 2H PbSO4 + H2O + reaction with concentrated nitric acid 2e– → 3Pb + 8HNO3 3Pb(NO3)2 + 2NO + Electrons are released to the electrode, pro- 4H2O ducing the negative charge. During charg- Tin gives hydrated Sn(IV) oxide. Concen- ing the reactions are reversed: – → 2– trated hydrochloric acid will not attack PbSO4 + 2e Pb + SO4 → + 2– lead. PbSO4 + 2H2O PbO2 + 4H + SO4 – Lead, like tin, forms halides, PbX2, with + 2e all halogens. PbCl4 is the only known lead(IV) halide (all halides of SnX4 are lead(II) carbonate (PbCO3) A white poi- known). The great stability of the Pb(II) sonous powder that occurs naturally as the state leads to Pb(IV) compounds being mineral cerussite. It forms rhombic crystals powerful oxidizing agents. and can be precipitated by reacting a cold Lead is used in accumulators aqueous solution of a soluble lead salt (e.g. (lead–acid), alloys, radiation shielding, and lead(II) nitrate) with ammonium carbon- water and sound proofing. It is also used in ate. the petrochemical, paint, and glass industries. lead(II) carbonate hydroxide (white ° Symbol: Pb; m.p. 327.5 C; b.p. lead; 2PbCO3.Pb(OH)2) The most impor- 1830°C; r.d. 11.35 (20°C); p.n. 82; r.a.m. tant basic lead carbonate. It can be manu- 207.2. factured electrolytically. It has been used as a pigment in white and colored paints but lead(II) acetate See lead(II) ethanoate. it has the considerable drawback that it is poisonous. lead–acid accumulator A type of electrical accumulator used in vehicle batteries. It lead-chamber process A former process has two sets of plates: spongy lead plates for the manufacture of sulfuric acid by ox- connected in series to the negative terminal idizing sulfur(IV) oxide with nitrogen and lead(IV) oxide plates connected to the monoxide. The reaction, which was car- positive terminal. The material of the elec- ried out in large lead chambers, has now trodes is held in a hard lead-alloy grid. The been replaced by the contact process. plates are interleaved. The electrolyte is dilute sulfuric acid. lead dioxide /dÿ-oks-ÿd, -id/ See lead(IV) The e.m.f. when fully charged is about oxide. 2.2 V. This falls to a steady 2 V when current is drawn. As the accumulator begins to lead(II) ethanoate (lead(II) acetate; run down, the e.m.f. falls further. During Pb(CH3CO2)2) A compound usually oc- discharge the electrolyte becomes more di- curring as the hydrate Pb(CH3CO2)2. lute and its relative density falls. To 3H2O, forming monoclinic crystals. At 160 Le Chatelier’s principle

100°C it loses ethanoic acid and water, ble sulfide. Lead(II) sulfide is useful as a forming a basic lead(II) ethanoate. Its solu- rectifier in electrical components. bility in water is 50 g per 100 g of water at 25°C. Lead(II) ethanoate can be obtained lead tetraethyl /tet-ră-eth-ăl/ (tetraethyl as an anhydrous salt. Its chief asset is that lead; Pb(CH2CH3)4) A poisonous liquid it is one of the few common lead(II) salts that is insoluble in water but soluble in or- that are soluble in water. ganic solvents. It is manufactured by the reaction of an alloy of sodium and lead with lead-free fuel Vehicle fuel that contains 1-chloroethane. The product is obtained none of the anti-knock agent lead by steam distillation. Lead tetraethyl is tetraethyl. See lead tetraethyl. used as an additive in internal-combustion engine fuel to increase its octane number lead(IV) hydride See plumbane. and thus prevent preignition (knocking). lead monoxide /mon-oks-ÿd, -id/ See leaving group The group leaving a mol- lead(II) oxide. ecule in a substitution or elimination reaction. The nature of the leaving group is lead(II) oxide (lead monoxide; PbO) A often an important factor in the progress of yellow crystalline powder formed by roast- the reaction. ing molten lead in air. Litharge, the most common form, is obtained when lead(II) Leblanc process /lă-blahnk/ An obsolete oxide is heated above its melting point. If process for the manufacture of sodium car- prepared below its melting point, another bonate. Sodium chloride is converted to form, called massicot, is obtained. Litharge sodium sulfate by heating with sulfuric is used in the rubber industry, in the man- acid. This sulfate is then roasted in a rotary ufacture of paints and varnishes, and in the furnace where it is first reduced to the sul- manufacture of lead glazes for pottery. fide using carbon, and then immediately converted to the carbonate by the action of lead(IV) oxide (lead dioxide; PbO2) A limestone. Sodium carbonate solution is dark-brown solid forming hexagonal crys- obtained by leaching with water and this is tals. On heating to 310°C it decomposes subsequently dried and calcined to obtain into lead(II) oxide and oxygen. It can be the solid. The process is named for the prepared electrolytically or by reacting French physician Nicolas Leblanc lead(II) oxide with potassium chlorate. (1742–1806). Lead(IV) oxide has been used in the manufacture of matches. Le Chatelier’s principle /lă-sha-tel-yayz/ If a system is at equilibrium and a change is lead(II) sulfate (PbSO4) A white crys- made in the conditions, the equilibrium ad- talline solid that occurs naturally as the justs so as to oppose the change. The prin- mineral anglesite. It is almost insoluble in ciple can be applied to the effect of water and can be precipitated by reacting temperature and pressure on chemical re- an aqueous solution containing sulfate ions actions. A good example is the Haber with a solution of a soluble lead(II) salt process for synthesis of ammonia: ˆ (e.g. lead(II) ethanoate). It forms basic N2 + 3H2 2NH3 lead(II) sulfates when shaken together with The ‘forward’ reaction → lead(II) hydroxide and water. Basic lead(II) N2 + 3H2 2NH3 sulfates are useful as pigments. is exothermic. Thus, reducing the temperature displaces the equilibrium towards pro- lead(II) sulfide (PbS) A black solid that duction of NH3 (as this tends to increase occurs naturally as the mineral galena. It temperature). Increasing the pressure also can be prepared as a precipitate by reacting favors formation of NH3, because this a solution of a soluble lead(II) salt with hy- leads to a reduction in the total number of drogen sulfide or with a solution of a solu- molecules (and hence pressure). The

161 Leclanché cell process is named for the French chemist an electron acceptor, but in common usage Henri Louis Le Chatelier (1850–1936). the terms Lewis acid and Lewis base are reserved for systems without acidic hydrogen Leclanché cell /lă-klahn-shay/ A primary atoms. The acid is named for the American voltaic cell consisting, in its ‘wet’ form, of physical chemist Gilbert Newton Lewis a carbon-rod anode and a zinc cathode, (1875–1946). with a 10–20% solution of ammonium chloride as electrolyte. Manganese(IV) Lewis base See Lewis acid. oxide mixed with crushed carbon in a porous bag or pot surrounding the anode Lewis octet theory See octet. acts as a depolarizing agent. The dry form (dry cell) is widely used for flashlight bat- Lewis structure (Lewis formula) A two- teries, transistor radios, etc. It has a mix- dimensional depiction, by means of chemi- ture of ammonium chloride, zinc chloride, cal element and electron dot symbols, of flour, and gum forming an electrolyte the possible structure of a molecule or ion, paste. Sometimes the dry cell is arranged in showing each atom in relation to its neigh- layers to form a rectangular battery, which bors, the bonds that hold the atoms to- has a longer life than the cylinder type. The gether, and the lone pairs in each atom’s cell is named for the French engineer and outer shell. inventor Georges Leclanché (1839–82). l-form See optical activity. LEED (low-energy electron diffraction) A method of electron diffraction that is used L-form See optical activity. to investigate surfaces. A surface is bombarded with a beam of low-energy elec- Liebig condenser /lee-big/ A simple type trons, with the diffracted electrons hitting of laboratory condenser. It consists of a a fluorescent screen or other detector. The straight glass tube, in which the vapor is electron beam has a low energy so that it condensed, with a surrounding glass jacket interacts with the surface rather than the through which cooling water flows. The bulk of the material. The technique gives condenser is named for the German useful information about the structure of chemist Justus von Liebig (1803–73). surfaces and processes occurring at surfaces. ligand /lig-ănd/ A molecule or ion that forms a coordinate bond to a metal atom leucine /loo-seen/ See amino acids. or ion in a COMPLEX. See also chelate. levo-form /lee-vo-form/ See optical activ- ligand-field theory See crystal-field the- ity. ory. levorotatory /lee-voh-roh-tă-tor-ee. -toh- light (visible radiation) A form of electro- ree/ See optical activity. magnetic radiation able to be detected by the human eye. Its wavelength range is be- Lewis acid /loo-is/ A substance that can tween about 400 nm (far red) and about accept an electron pair to form a coordi- 700 nm (far violet). The boundaries are not nate bond; a Lewis base is an electron-pair precise as individuals vary in their ability to donor. In this model, the neutralization re- detect extreme wavelengths; this ability action is seen as the acquisition of a stable also declines with age. octet by the acid, for example: → Cl3B + :NH3 Cl3B:NH3 lignite /lig-nÿt/ (brown coal) The poorest Metal ions in coordination compounds grade of coal, containing up to 45% car- are also electron-pair acceptors and there- bon and with a high moisture content. fore Lewis acids. The definition includes the ‘traditional’ Brønsted acids since H+ is ligroin /lig-roh-in/ A mixture of hydrocar-

162 liquid crystal bons obtained from PETROLEUM, used as a linolenic acid /lin-ŏ-lee-nik, -len-ik/ general solvent. It has a boiling range of 80 (C17H29COOH) A liquid unsaturated car- to 120°C. boxylic acid that occurs in LINSEED OIL and other plant oils. It contains three double lime See calcium oxide; calcium hydrox- bonds. ide. linseed oil An oil extracted from the seeds limestone A natural form of calcium car- of flax (linseed). It hardens on exposure to bonate. It is used in making calcium com- air (it is a drying oil) because it contains pounds, carbon dioxide, and cement. LINOLEIC ACID and LINOLENIC ACID, and is used in enamels, paints, putty, and var- lime water A solution of calcium hydrox- nishes. ide in water. If carbon dioxide is bubbled lipid /lip-id/ A collective term used to de- through lime water a milky precipitate of scribe a group of substances in cells char- calcium carbonate forms. Prolonged bub- acterized by their solubility in organic bling of carbon dioxide turns the solution solvents such as ether and benzene, and clear again as a result of the formation of their low solubility in water. The group is soluble calcium hydrogencarbonate rather heterogeneous in terms of both (Ca(HCO3)2). function and structure. The simple lipids include neutral lipids or glycerides, which limonite /lÿ-mŏ-nÿt/ (bog iron ore) A are esters of glycerol and fatty acids, and dark-colored mineral that consists mainly the waxes, which are esters of long-chain of the hydroxide and oxides of iron, a monohydric alcohols and fatty acids. major iron ore. It is also used as a pigment. liquefied natural gas /lik-wĕ-fÿd/ (LNG) Linde process /lin-dĕ/ A method of lique- Liquid METHANE, obtained from NATURAL fying gases by compression followed by ex- GAS and used as a fuel. pansion through a nozzle. The process is used for producing liquid oxygen and ni- liquefied petroleum gas (LPG) A mix- trogen by liquefying air and then fraction- ture of liquefied hydrocarbon gases ating it. It is named for the German (mainly PROPANE) extracted from PETRO- engineer Karle von Linde (1842–1934). LEUM, used as a fuel for internal combustion engines and for heating. line defect See defect. liquid The state of matter in which the particles of a substance are loosely bound line spectrum A SPECTRUM composed of a number of discrete lines corresponding to by intermolecular forces. The weakness of these forces permits movement of the par- single wavelengths of emitted or absorbed ticles and consequently liquids can change radiation. Line spectra are produced by their shape within a fixed volume. The liq- atoms or simple (monatomic) ions in gases. uid state lacks the order of the solid state. Each line corresponds to a change in elec- Thus, amorphous materials, such as glass, tron orbit, with emission or absorption of in which the particles are disordered and radiation. can move relative to each other, can be classed as liquids. linkage isomerism See isomerism. liquid air A pale blue liquid. It is a mix- linoleic acid /lin-ŏ-lee-ik, lă-noh-lee-ik/ ture of liquid oxygen (boiling at –183°C) (C17H31COOH) An unsaturated car- and liquid nitrogen (boiling at –196°C). boxylic acid that occurs in LINSEED OIL and other plant oils. It is used in making paints liquid crystal A substance that can flow and varnishes. like a viscous liquid but has a considerable

163 liter amount of molecular order. There are The element reacts with hydrogen to three types of liquid crystal. In a smectic form lithium hydride, LiH, a colorless crystal there are layers of aligned mole- high-melting solid, which releases hydro- cules, with the long axes of the molecules gen at the anode during electrolysis (con- being perpendicular to the layers. In a cho- firming the ionic nature Li+H–). The lesteric crystal there are also layers of compound reacts with water to release hy- aligned molecules, but with the axes of the drogen and is also frequently used as a re- molecules being parallel to the planes of ducing agent in organometallic synthesis. the layers. In a nematic crystal the mol- Lithium reacts with oxygen to give Li2O ecules are all aligned in the same direction (sodium gives the peroxide) and with ni- but not arranged in layers. trogen to form Li3N on fairly gentle warming. The metal itself reacts only slowly with liter /lee-ter/ Symbol: l A unit of volume water, giving the hydroxide (LiOH) but now defined as 10–3 meter3; i.e. 1000 cm3. lithium oxide reacts much more vigorously The milliliter (ml) is thus the same as the to give again the hydroxide; the nitride is cubic centimeter (cm3). However, the name hydrolyzed to ammonia. The metal reacts is not recommended for precise measure- with halogens to form halides (LiX). ments since the liter was formerly defined Apart from the fluoride the halides are as the volume of one kilogram of pure readily soluble both in water and in oxy- water at 4°C and standard pressure. On gen-containing organic solvents. In this this definition, one liter is the same as property lithium partly resembles magnesium which has a similar charge/size ratio. 1000.028 cubic centimeters. Compared to the other carbonates of group 1, lithium carbonate is thermally un- litharge /lith-arj/ See lead(II) oxide. stable decomposing to Li2O and CO2. This is because the small Li+ ion leads to partic- lithia /lith-ee-ă/ See lithium oxide. ularly high lattice energies favouring the formation of Li O. lithia water See lithium hydrogencarbon- 2 Lithium also forms a wide range of ate. alkyl- and aryl-compounds with organic compounds, which are particularly useful lithium /lith-ee-ŭm/ A light silvery moder- in organic synthesis. Lithium compounds ately reactive metal; the first member of the impart a characteristic purple color to alkali metals (group 1 of the periodic flames. table). It occurs in a number of complex sil- Symbol: Li; m.p. 180.54°C; b.p. icates, such as spodumene, lepidolite, and 1347°C; r.d. 0.534 (20°C); p.n. 3; r.a.m. petalite, and a mixed phosphate, tryphilite. 6.941. It is a rare element accounting for 0.0065% of the Earth’s crust. Lithium ores lithium aluminum hydride See lithium are treated with concentrated sulfuric acid tetrahydridoaluminate(III). and lithium sulfate subsequently separated by crystallization. The element can be ob- lithium carbonate (Li2CO3) A white tained by conversion to the chloride and solid obtained by the addition of excess electrolysis of the fused chloride or of solu- sodium carbonate solution to a solution of tions of LiCl in pyridine. a lithium salt. It is soluble in the presence Lithium has the electronic configura- of excess carbon dioxide, forming lithium tion 1s22s1 and is entirely monovalent in its hydrogencarbonate. If heated (to 780°C) in chemistry. The lithium ion is, however, a stream of hydrogen it undergoes thermal much smaller than the ions of the other al- decomposition to give lithium oxide and kali metals; consequently it is polarizing carbon dioxide. Lithium carbonate forms and a certain degree of covalence occurs in monoclinic crystals and differs from the its bonds. Lithium also has the highest ion- other group 1 carbonates in being only ization potential of the alkali metals. sparingly soluble in water. It has a close re-

164 localized bond semblance to the carbonates of magnesium lithium oxide (lithia; Li2O) A white solid and calcium – an example of a diagonal reproduced by burning metallic lithium in air lationship in the periodic table. above its melting point. It can also be produced by the thermal decomposition of the lithium chloride (LiCl) A white solid carbonate or hydroxide. Lithium oxide reproduced by dissolving lithium carbonate acts slowly with water forming a solution or oxide in dilute hydrochloric acid and of lithium hydroxide; the reaction is crystallizing the product. Below 19°C the exothermic. The compound has a calcium- dihydrate (LiCl.2H2O) is obtained; at fluoride structure. 19°C the chloride loses one molecule of water and becomes anhydrous at 93.5°C. lithium sulfate (Li2SO4) A white solid Lithium chloride is used as a flux in weld- prepared by the addition of excess lithium ing aluminum. The compound forms cubic oxide or carbonate to a solution of sulfuric crystals; the anhydrous salt is isomorphous acid. It is readily soluble in water from with sodium chloride. It dissolves in such which it crystallizes as the monohydrate. In organic solvents as alcohols, ketones, and contrast to the other group 1 sulfates it esters. Lithium chloride is probably the does not form alums and it is not isomor- most deliquescent substance known and phous with these other sulfates. forms hydrates with 1, 2, and 3 molecules tet- of water. lithium tetrahydridoaluminate(III) / ră-hÿ-dri-doh-ă-loo-mă-nit, -nayt/ (lithium lithium hydride (LiH) A white crystalline aluminum hydride; LiAlH4) A white solid produced by action of lithium hydride on solid produced by direct combination of aluminum chloride, the hydride being in the elements at a temperature above excess. Lithium tetrahydridoaluminate re- 500°C. Electrolysis of the fused salt yields acts violently with water. It is a powerful hydrogen at the anode. Lithium hydride re- reducing agent, reducing ketones and car- acts violently with water to give lithium boxylic acids to their corresponding alco- hydroxide and hydrogen; the reaction is hols. In inorganic chemistry it is used in the highly exothermic. The compound is used preparation of hydrides. as a reducing agent and in the preparation of other hydrides. Lithium hydride has a litmus /lit-mŭs/ A natural pigment that cubic structure and is more stable than the changes color when in contact with acids group 1 hydrides. and alkalis; above a pH of 8.3 it is blue and below a pH of 4.5 it is red. Thus it gives a lithium hydrogencarbonate (LiHCO3) rough indication of the acidity or basicity A compound known only in solution, proof a solution; because of its rather broad duced by the action of carbon dioxide, range of color change it is not used for pre- water, and lithium carbonate. When a so- cise work. Litmus is used both in solution lution of the hydrogencarbonate is heated, and as litmus paper. carbon dioxide and lithium carbonate are produced. Solutions of the hydrogencar- lixiviation /lik-siv-ee-ay-shŏn/ The pro- bonate are sold and used in medicine under cess of separating soluble components the name of lithia water. from a mixture by washing them out with water. lithium hydroxide (LiOH) A white solid made industrially as the monohydrate LNG See liquefied natural gas. (LiOH.H2O) by reacting lime with a lithium ore or with a salt made from the localized bond A bond in which the elec- ore. Lithium hydroxide has a closer resem- trons contributing to the bond remain be- blance to the group 2 hydroxides than to tween the two atoms concerned, i.e. the the group 1 hydroxides. bonding orbital is localized. The majority

165 lodestone of bonds are of this type. Compare delo- LPG See liquefied petroleum gas. calized bond. LSD See lysergic acid diethylamide. lodestone /lohd-stohn/ A naturally occurring magnetic oxide of iron, a form of MAG- lumen /loo-mĕn/ (pl. lumens or lumina) NETITE (Fe3O4). A piece of lodestone is a Symbol: lm The SI unit of luminous flux, natural magnet and lodestones were used equal to the luminous flux emitted by a as magnetic compasses in ancient times. point source of one candela in a solid angle of one steradian. 1 lm = 1 cd sr. lone pair A pair of valence electrons having opposite spin that are located together luminescence /loo-mă-ness-ĕns/ The on one atom, i.e. are not shared as in a co- emission of radiation from a substance in valent bond. Lone pairs occupy similar po- which the particles have absorbed energy sitions in space to bond pairs and account and gone into excited states. They then re- for the shapes of molecules. A molecule turn to lower energy states with the emis- with a lone pair can donate this to an elec- sion of electromagnetic radiation. If the tron acceptor, such as H+ or a metal ion, to luminescence persists after the source of form coordinate bonds. See complex; excitation is removed the process is called Lewis base. phosphorescence: if not, it is called fluorescence. long period See period. lutetium /loo-tee-shee-ŭm/ A silvery ele- lowering of vapor pressure A colliga- ment of the lanthanoid series of metals. It tive property of solutions in which the occurs in association with other lanthanoids. Lutetium is a very rare lan- vapor pressure of a solvent is lowered as a thanoid and has few uses. solute is introduced. When both solvent Symbol: Lu; m.p. 1663°C; b.p. 3395°C; and solute are volatile the effect of increas- r.d. 9.84 (25°C); p.n. 71; r.a.m. 174.967. ing the solute concentration is to lower the partial vapor pressure of each component. lux /luks/ (pl. lux) Symbol: lx The SI unit When the solute is a solid of negligible of illumination, equal to the illumination vapor pressure the lowering of the vapor produced by a luminous flux of one lumen pressure of the solution is directly propor- falling on a surface of one square meter. 1 tional to the number of species introduced lx = 1 lm m–2. rather than to their nature and the proportionality constant is regarded as a general Lyman series /lÿ-măn/ See hydrogen solvent property. Thus the introduction of atom spectrum. It is named for the Ameri- the same number of moles of any solute can physicist Theodore Lyman (1874– causes the same lowering of vapor pres- 1954). sure, if dissociation does not occur. If the solute dissociates into two species on dis- lyophilic /lÿ-ŏ-fil-ik/ Solvent attracting. solution the effect is doubled. The kinetic When the solvent is water, the word hy- model for the lowering of vapor pressure drophilic is often used. The terms are ap- treats the solute molecules as occupying plied to: part of the surface of the liquid phase and 1. Ions or groups on a molecule. In aque- thereby restricting the escape of solvent ous or other polar solutions ions or molecules. The effect can be used in the polar groups are lyophilic. For example, measurement of relative molecular masses, the –COO– group on a soap is the particularly for large molecules, such as lyophilic (hydrophilic) part of the mole- polymers. See also Raoult’s law. cule. 2. The disperse phase in colloids. In Lowry–Brønsted theory /low-ree bron- lyophilic colloids the dispersed particles sted/ See acid. have an affinity for the solvent, and the

166 lysine colloids are generally stable. Compare easily solvated. Gold and sulfur sols are lyophobic. examples. Compare lyophilic. lyophobic /lÿ-ŏ-foh-bik/ Solvent re- lysergic acid diethylamide /lÿ-ser-jik; dÿ- pelling. When the solvent is water, the eth-ăl-am-ÿd/ (LSD) A synthetic organic word hydrophobic is used. The terms are compound that has physiological effects applied to: similar to those produced by alkaloids in 1. Ions or groups on a molecule. In aque- certain fungi. Even small quantities, if in- ous or other polar solvents, the lyophobic group will be non-polar. For gested, produce hallucinations and ex- example, the hydrocarbon group on a treme mental disturbances. The initials soap molecule is the lyophobic (hy- LSD come from the German form of the drophobic) part. chemical’s name, Lysergic-Saure-Diathy- 2. The disperse phase in colloids. In lamide. lyophobic colloids the dispersed particles are not solvated and the colloid is lysine /lÿ-seen, -sin/ See amino acids.

167 M

macromolecular crystal /mak-roh-mŏ- Magnesium halides are also formed by lek-yŭ-ler/ A crystal composed of atoms direct reaction with the halogen. They joined together by covalent bonds, which show a slight deviation in the general be- form giant three-dimensional or two- havior of halides by dissolving normally in dimensional networks. Diamond and sili- water and only undergoing a significant cates are examples of macromolecular amount of hydrolysis when solutions are crystals. evaporated: → MgX2 + 2H2O Mg(OH)2 + 2HX macromolecule /mak-roh-mol-ĕ-kyool/ A Magnesium hydroxide is considerably large molecule; e.g. a natural or synthetic less soluble than the hydroxides of the polymer. heavier elements in group 2 and is a weaker base. It forms a soluble sulfate, chlorate, magic acid See superacid. and nitrate. Like the heavier alkaline earths, magnesium forms an insoluble car- magnesia /mag-nee-zhă, -shă/ See magne- bonate, but MgCO3 is the least thermally sium oxide. stable of the group. Unlike calcium, it does not form a carbide. magnesite /mag-nĕ-sÿt/ A mineral form of Magnesium metal is industrially impor- magnesium carbonate, MgCO3. tant as a major component in lightweight alloys (with aluminum and zinc). The magnesium /mag-nee-zee-ŭm, -seee-ŭm/ metal surfaces develop an impervious A light metallic element; the second mem- oxide film which protects them from pro- ber of group 2 of the periodic table (the gressive deterioration. alkaline earths). It has the electronic con- Because of its ionic nature magnesium figuration of neon with two additional forms very few coordination compounds, outer 3s electrons. The element accounts for Donor–acceptor species in aqueous solu- 2.09% of the Earth’s crust and is eighth in tions are short-lived, but magnesium bro- order of abundance. It occurs in a wide va- mide and iodide have sufficient acceptor riety of minerals such as brucite (Mg(OH)2), properties to dissolve in donor solvents carnallite (MgCl2.KCl.6H2O), epsomite such as alcohols and ketones. Magnesium (MgSO4. 7H2O), magnesite (MgCO3), and appears to be an essential element for life, dolomite (MgCO3.CaCO3); and also as occurring in chlorophyll. MgCl2 in sea water. The metal is obtained Certain specialized organometallic com- by several routes, depending on the mineral pounds of magnesium are important in or- used, but all leading to the chloride. This is ganic chemistry as synthetic reagents. followed by electrolysis of the fused chlo- Magnesium forms Grignard reagents, ride. RMgX, and related di-alkyls, R2Mg, by re- The element has a fairly low ionization action of the metal directly with the alkyl potential and is an electropositive element. bromide or iodide. It reacts directly with oxygen, nitrogen, The element crystallizes with the close- and sulfur on heating, to form the oxide, packed hexagonal structure. ° ° MgO, the nitride, Mg3N2, and the sulfide Symbol: Mg; m.p. 649 C; b.p. 1090 C; MgS. r.d. 1.738 (20°C); p.n. 12; r.a.m. 24.3050.

168 magnetic permeability magnesium bicarbonate See magnesium weakly basic because of the attraction of hydrogencarbonate. the oxide ions for protons from water molecules: 2– → – magnesium carbonate (MgCO3) A O + H2O 2OH white solid that occurs naturally as the Magnesium oxide melts at 2800°C and is mineral magnesite and in association with widely used as a refractory lining for fur- calcium carbonate in dolomite. Magne- naces. sium carbonate is sparingly soluble in water but reacts with dilute acids to give magnesium peroxide (MgO2) A white the salt, carbon dioxide, and water. Be- insoluble solid prepared by reacting cause of this it is used in medicine as a mild sodium or barium peroxide with a concen- antacid. Magnesium carbonate also de- trated solution of a magnesium salt. Mag- composes easily to give magnesium oxide, nesium peroxide is used as a bleach for which is an important refractory material. dyestuffs and silks. magnesium chloride (MgCl2) A solid magnesium sulfate (MgSO4) A solid that that exists in a variety of hydrated forms, occurs naturally in many salt deposits in most commonly as the hexahydrate, combination with other minerals. One hy- MgCl2.6H2O. When heated, this hydrated drated form, MgSO4.7H2O, is known as form is hydrolyzed by its water of crystal- Epsom salt or epsomite. Epsom salt is lization, with the evolution of hydrogen made on a commercial scale by reacting chloride and the formation of the oxide: magnesium carbonate with sulfuric acid. → MgCl2 + H2O MgO + 2HCl Magnesium sulfate is used as a purgative The anhydrous chloride must therefore be drug and as an antidote for barium and prepared by evaporating an aqueous solu- barbiturate poisoning. It is also used in the tion in an atmosphere of hydrogen chlo- dyeing and sizing of textiles, in synthetic ride. It is used in the preparation of cotton fiber production, and as a source of mag- fabrics. nesium in fertilizers. magnesium hydrogencarbonate (mag- magnetic constant See magnetic perme- nesium bicarbonate; Mg(HCO3)2) The ability. solid hydrogencarbonate is unknown at room temperature. The compound is pro- magnetic moment The ratio of the duced in solution when water containing torque exerted on a magnet or a loop that carbon dioxide dissolves magnesium car- carries an electrical current or on a moving bonate: electrical charge in a magnetic field to the → MgCO3 + H2O + CO2 Mg(HCO3)2 field strength of that magnetic field. An It is a cause of temporary hardness in electron has an orbital magnetic moment water. because of the magnetic field generated by its orbital motion round the nucleus and a magnesium hydroxide (Mg(OH)2) A spin magnetic moment because of its quan- white solid that dissolves sparingly in tum mechanical spin. Atomic nuclei can water to give an alkaline solution. It can be also have magnetic moments because of prepared by adding an alkali to a soluble their spin. The existence of electron and magnesium compound. Magnesium hy- nuclear magnetic moments is made use of droxide is used in medicine as an antacid. in various branches of spectroscopy and in magnetochemistry. magnesium oxide (magnesia; MgO) A white solid that occurs naturally as the magnetic permeability symbol µ. A mineral periclase. It can be prepared by quantity that characterizes the response of heating magnesium in oxygen or by de- a medium to a magnetic field. The perme- µ composition of magnesium hydroxide, car- ability of free space, which is denoted 0 bonate, or nitrate. Magnesium oxide is and is also called the magnetic constant has

169 magnetic quantum number the value 4π×10–7 Hm–1 in SI units. The effect, also involves electron spin and the magnetic permeability of a medium relates alignment of magnetic moments in do- the magnetic flux density B to the magnetic mains. field strength H by the equation: B = µH. The relative magnetic permeability of a magnetite /mag-nĕ-tÿt/ A black mineral µ µ µ . medium is defined by = r 0 form of iron(II)–iron(III) oxide, Fe2O3, a major type of iron ore. It is also used as a magnetic quantum number See atom. flux in making ceramics. See also lodestone. magnetic separation A method of separating crushed mineral mixtures using the magnetochemistry /mag-nee-toh-kem- magnetic properties that a component may iss-tree/ The use of magnetic measurements possess, such as ferromagnetism or dia- to give information about bonding. magnetism. magneton /mag-nĕ-ton/ Symbol µ. A unit magnetic susceptibility Symbol χ. A di- for measuring magnetic moments at the mensionless quantity, related to the MAG- atomic and subatomic scales. The Bohr NETIC PERMEABILITY of a medium, that µ µ π characterizes the magnetic nature of that magneton B is given by B = eh/4 me, medium. The relation between the mag- where e and m are the charge and mass of netic susceptibility and the relative mag- an electron respectively, and h is the Planck µ χ µ –1 constant. The Bohr magneton is the small- netic permeability r is given by = r . If the material is diamagnetic χ has a small est unit the orbital magnetic moment of an negative value. If the material is paramag- electron in an atom can have. The nuclear µ netic χ has a small positive value. If the ma- magneton N is given by replacing the mass terial is ferromagnetic χ has a large positive of the electron by the mass of the proton value. and is therefore about 1840 times smaller than the Bohr magneton. magnetism /mag-nĕ-tiz-ăm/ The study of the nature and cause of magnetic force malachite /mal-ă-kÿt/ A green mineral fields, and how different substances are af- consisting of copper(II) carbonate and hy- fected by them. Magnetic fields are pro- droxide (CuCO3.Cu(OH)2). It is used as an duced by moving charge – on a large scale ore and a pigment. (as with a current in a coil, forming an elec- tromagnet), or on the small scale of the maleic acid /mă-lee-ik/ See butenedioic moving charges in the atoms. It is generally acid. assumed that the Earth’s magnetism and that of other planets, stars, and galaxies malic acid /mal-ik/ (2-hydroxybutane- have the same cause. dioic acid; HCOOCH CH(OH)COOH) A Substances may be classified on the 2 colorless crystalline carboxylic acid that is basis of how samples interact with fields. found in unripe fruits. It tastes of apples Different types of magnetic behavior result from the type of atom. Diamagnetism, and is used in food flavorings. which is common to all substances, is due to the orbital motion of electrons. Para- malonic acid /mă-lon-ik/ See propane- magnetism is due to electron spin, and a dioic acid. property of materials containing unpaired electrons. It is particularly important in maltose /môl-tohs/ (C12H22O11) A sugar transition-metal chemistry, in which the found in germinating cereal seeds. It is a complexes often contain unpaired elec- disaccharide composed of two glucose trons. Magnetic measurements can give in- units. Maltose is an important intermedi- formation about the bonding in these ate in the enzyme hydrolysis of starch. It is complexes. Ferromagnetism, the strongest further hydrolyzed to glucose.

170 mannose manganate(VI) /mang-gă-nayt/ A salt ture as braunite (3Mn2O3.MnSiO3) and 2– containing the ion MnO4 . the monohydrate (Mn2O3.H2O) occurs in the mineral manganite. The manganese(III) manganate(VII) (permanganate) A salt oxide crystal lattice contains Mn3+ and O2– – containing the ion MnO4 . ions. With concentrated alkalis, it under- Manganate(VII) salts are purple, and goes disproportionation to give man- strong oxidizing agents. In basic solutions ganese(II) and manganese(IV) ions. the dark green manganate(VI) ion is formed. manganese(IV) oxide (manganese dioxide; MnO2) A black powder prepared by manganese /mang-gă-neez, -nees/ A tran- the action of heat on manganese(II) nitrate. sition metal occurring naturally as oxides, A hydrated form occurs naturally as the e.g. pyrolusite (MnO2). Nodules found on mineral pyrolusite. Manganese(IV) oxide is the ocean floor are about 25% manganese. insoluble in water. It is a powerful oxidiz- Its main use is in alloy steels made by ing agent: it reacts with hot concentrated adding pyrolusite to iron ore in an electric hydrochloric acid to produce chlorine and furnace. Manganese decomposes cold with warm sulfuric acid to give oxygen. water and dilute acids to give hydrogen The dihydrate (MnO2.2H2O) is formed and reacts with oxygen and nitrogen when when potassium manganate(VII) is re- heated. The oxidation states are +7, +6, +4, duced in alkaline solution. It is used as a and (the most stable) +2. Manganese(II) catalyst in the laboratory preparation of salts are pale pink and with alkali the solu- chlorine, as a depolarizer in electric dry tions precipitate manganese(II) hydroxide, cells, and in the glass industry. At which rapidly oxidizes in air to brown 500–600°C, manganese(IV) oxide decom- manganese(III) oxide. poses to give manganese(III) oxide and tri- Symbol: Mn; m.p. 1244°C; b.p. manganese tetroxide. It has a good 1962°C; r.d. 7.44 (20%C); p.n. 25; r.a.m. electrical conductivity. 54.93805. ses-kwee-oks- manganese dioxide /dÿ-oks-ÿd, -id/ See manganese sesquioxide / manganese(IV) oxide. ÿd, -id/ See manganese(III) oxide. manganese(II) oxide (manganous oxide; manganic oxide /man-gan-ik/ See man- MnO) A green powder prepared by heat- ganese(III) oxide. ing manganese(II) carbonate or oxalate in the absence of air. Alternatively it may be manganin /mang-gă-nin/ An alloy of cop- prepared by heating the higher manganese per, manganese, and nickel. It has a high oxides in a stream of hydrogen. Man- electrical resistivity and is used to make re- ganese(II) oxide is a basic oxide and is al- sistors. most insoluble in water. At high temperatures it is reduced by hydrogen to manganous oxide /mang-gă-nŭs/ See manganese. On exposure to air, man- manganese(II) oxide. ganese(II) oxide rapidly oxidizes. The compound has a crystal lattice similar to that of mannitol /man-ă-tol, -tohl/ (HOCH2- sodium(I) chloride. (CHOH)4CH2OH) A soluble hexahydric alcohol that occurs in many plants and manganese(III) oxide (manganic oxide; fungi. It is used in medicines and as a manganese sesquioxide; Mn2O3) A black sweetener (particularly in foods for diabet- powder obtained by igniting ics). It is an isomer of sorbitol. manganese(IV) oxide or a manganese(II) salt in air at 800°C. It reacts slowly with mannose /man-ohs/ (C6H12O6) A simple cold dilute acids to form manganese(III) sugar found in many polysaccharides. It is salts. Manganese(III) oxide occurs in na- an aldohexose, isomeric with glucose.

171 manometer manometer /mă-nom-ĕ-ter/ A device for body determines its tendency to resist measuring pressure. A simple type is a U- change in motion; the gravitational mass shaped glass tube containing mercury or determines its gravitational attraction for other liquid. The pressure difference be- other masses. The SI unit of mass is the tween the arms of the tube is indicated by kilogram. the difference in heights of the liquid. mass action, law of At constant temper- marble A dense mineral form of calcium ature, the rate of a chemical reaction is di- carbonate (CaCO3), formed from lime- rectly proportional to the active mass of stone. the reactants, the active mass being taken as the concentration. In general, the rate of Markovnikoff’s rule /mar-koff-ni-koffs/ reaction decreases steadily as the reaction A rule that predicts the quantities of the proceeds; a measure of the concentration products formed when an acid (HA) adds of any of the reactants will give a measure to the double bond in an alkene. If the of the rate of reaction. alkene is not symmetrical two products For the reaction A + B → products, the may result; for instance (CH3)2C:CH2 can law of mass action states that yield either (CH3)2HCCH2A or rate = k[A][B] (CH3)2ACCH3. The rule states that the where [A] represents the concentration of major product will be the one in which the A in mol dm–3 and k is a constant depen- hydrogen atom attaches itself to the carbon dent on the reaction. The term active mass atom with the larger number of hydrogen can equal the concentration in mol dm–3 atoms. In the example above, therefore, the only if there is no interaction or interfer- major product is (CH3)2ACCH3. ence between the reacting molecules. Many The Markovnikoff rule is explainable if systems exhibit interactions and interfer- the mechanism is ionic. The first step is ad- ence and consequently the concentration dition of H+ to one side of the double bond, has to be multiplied by an activity coeffi- forming a carbonium ion. The more stable cient in order to obtain the effective active form of carbonium ion will be the form in mass. See activity coefficient. which the positive charge appears on the carbon atom with the largest number of mass-energy equation The equation E = alkyl groups – thus the hydrogen tends to mc2, where E is the total energy (rest-mass attach itself to the other carbon. The posi- energy + kinetic energy + potential energy) tive charge is partially stabilized by the of a mass m, c being the speed of light. The electron-releasing (inductive) effect of the equation is a consequence of Einstein’s alkyl groups. Special theory of relativity; mass is a form Additions of this type do not always of energy and energy also has mass. Con- follow the Markovnikoff rule. Under cer- version of rest-mass energy into kinetic en- tain conditions the reaction may involve ergy is the source of power in radioactive the free radicals H• and A•, in which case substances and the basis of nuclear-power the opposite (anti-Markovnikoff) effect oc- generation. curs. The rule is named for the Russian chemist Vladimir Vasilyevich Markov- massicot /mass-ă-kot/ See lead(II) oxide. nikoff (1838–1904). mass number See nucleon number. marsh gas Methane that is produced in marshes by decomposing vegetation. mass spectrometer An instrument for producing ions in a gas and analyzing them Marsh’s test See arsine. according to their charge/mass ratio. The earliest experiments by J. J. Thomson used mass Symbol: m A measure of the quan- a stream of positive ions from a discharge tity of matter in an object. Mass is deter- tube, which were deflected by parallel elec- mined in two ways: the inertial mass of a tric and magnetic fields at right angles to

172 membrane the beam. Each type of ion formed a para- step 1 bolic trace on a photographic plate (a mass Cl:Cl → 2Cl• spectrograph). step 2 → In modern instruments, the ions are Cl• + CH4 HCl + CH3• produced by ionizing the gas with elec- step 3 → trons. The positive ions are accelerated out CH3• + Cl:Cl CH3Cl + Cl• of this ion source into a high-vacuum region. Here, the stream of ions is deflected mega- Symbol: M A prefix denoting 106. and focused by a combination of electric For example, 1 megahertz (MHz) = 106 and magnetic fields, which can be varied so hertz (Hz). that different types of ion fall on a detector. In this way, the ions can be analyzed ac- meitnerium /mÿt-neer-ee-ŭm/ A radioac- cording to their mass, giving a mass spec- tive metallic element not found naturally trum of the material. Mass spectrometers on Earth. Only a few atoms of the element are used for accurate measurements of rel- have ever been detected; it can be made by ative atomic mass and for analysis of iso- bombarding a bismuth target with iron nu- tope abundance. They can also be used to clei. The isotope 266Mt has a half-life of identify compounds and analyze mixtures. about 3.4 × 10–3s. An organic compound bombarded with Symbol: Mt; p.n. 109. electrons forms a number of fragment ions. (Ethane (C2H6), for instance, might form mel-ă-mÿn + + + melamine / / (triaminotriazine; CH , C2H5 , CH2 , etc.) The relative pro- C3N3(NH2)3) A white solid organic com- portions of different types of ions is used to pound whose molecules consist of a six- find the structure of new compounds. The membered heterocyclic ring of alternate characteristic spectrum can also identify carbon and nitrogen atoms with three compounds by comparison with standard amino groups attached to the carbons. spectra. Condensation polymerization with methanal or other aldehydes produces mass spectrum See mass spectrometer. melamine resins, which are important ther- matrix /may-triks, mat-riks/ (pl. matrices mosetting plastics. or matrixes) A continuous solid phase in which particles of a different solid phase melting (fusion) The process by which a are embedded. solid is converted into a liquid by heat or pressure. matte /mat/ A mixture of iron and copper sulfides obtained at an intermediate stage melting point The temperature at which in smelting copper ores. a solid is in equilibrium with its liquid phase at standard pressure and above maxwell /maks-wĕl/ Symbol: Mx A unit which the solid melts. This temperature is of magnetic flux used in the c.g.s. system. It always the same for a particular solid. Ion- is equal to 10–8 Wb. The unit is named for ically bonded solids generally have much the British physicist James Clerk Maxwell higher melting points than those in which (1831–79). the forces are covalent or intermolecular. mechanism A step-by-step description of membrane A thin pliable sheet of tissue the events taking place in a chemical reac- or other material acting as a boundary. The tion. It is a theoretical framework account- membrane may be either natural (as in ing for the fate of bonding electrons and cells, skin, etc.) or synthetic modifications illustrates which bonds are broken and of natural materials (cellulose derivatives which are formed. For example, in the or rubbers). In many physicochemical chlorination of methane to give studies membranes are supported on chloromethane: porous materials, such as porcelain, to pro-

173 mendelevium vide mechanical strength. Membranes are special amalgams for dentistry, scientific generally permeable to some degree. apparatus, and in mercury cells. Mercury Membranes can be prepared to permit compounds are used as fungicides, timber the passage of other molecules and micro- preservatives, and detonators. molecular material. Because of permeabil- Symbol: Hg; m.p. –38.87°C; b.p. ity effects, concentration diffferences at a 356.58°C; r.d. 13.546 (20°C); p.n. 80; membrane give rise to a whole range of r.a.m. 200.59. See amalgam; zinc group. membrane-equilibrium studies, of which osmosis, dialysis, and ultrafiltration are ex- mercury cell A voltaic or electrolytic cell amples. See also semipermeable mem- in which one or both of the electrodes con- brane. sists of mercury or an amalgam. Amalgam electrodes are used in the Daniell cell and mendelevium /men-dĕ-lee-vee-ŭm/ A ra- the Weston cadmium cell. Flowing mer- dioactive transuranic element of the acti- cury electrodes are also used in electrolytic noid series, not found naturally on Earth. cells (see polarography). In the production Several short-lived isotopes have been syn- of chlorine, sodium chloride solution is thesized. electrolyzed in a cell with carbon anodes Symbol: Md; p.n. 101; most stable iso- and a flowing mercury cathode. At the 258 tope Md (half-life 57 minutes). cathode, sodium metal is formed, which forms an amalgam with the mercury. Mendius reaction /men-dee-ŭs/ The reduction of the cyanide group to a primary mercury(I) chloride (mercurous chloride; amine group using sodium in alcohol: calomel; Hg Cl ) A white precipitate pre- RCN + 2H → RCH NH 2 2 2 2 2 pared by adding dilute hydrochloric acid to It is a method of increasing the chain length a mercury(I) salt solution or by subliming of compounds in ascending a homologous mercury(II) chloride with mercury. Mer- series. cury(I) chloride is sparingly soluble in water and is blackened by both ammonia mer See polymer. gas, which it absorbs, and by alkalis. It was formerly used as a purgative. mercaptan /mer-kap-tăn/ See thiol. mercuric chloride /mer-kyoo-rik/ See mercury(II) chloride (mercuric chloride; mercury(II) chloride. corrosive sublimate; HgCl2) A colorless crystalline compound prepared by direct mercuric oxide See mercury(II) oxide. combination of mercury with cold dry chlorine. Mercury(II) chloride is soluble in mercuric sulfide See mercury(II) sulfide. water; it also dissolves in concentrated hydrochloric acid because of the formation of 2– – mercurous chloride /mer-kyoo-rŭs/ See complex ions, HgCl4 and HgCl3 . On mercury(I) chloride. heating, mercury(II) chloride sublimes forming a white translucent mass. It is ex- mercurous oxide See mercury(I) oxide. tremely poisonous, but in dilute solution (1:1000) it is used as an antiseptic. mercurous sulfide See mercury(I) sulfide. mercury(I) oxide (mercurous oxide; Hg2O) The black precipitate formed on mercury /mer-kyŭ-ree/ A transition metal addition of sodium hydroxide solution to a that occurs naturally as cinnabar (mer- solution of mercury(I) nitrate is thought by cury(II) sulfide); small drops of metallic some to be mercury(I) oxide; others, who mercury also occur in cinnabar and in doubt its existence, think that the black- some volcanic rocks. The vapor is very poi- ness of the precipitate is due to some free sonous. Mercury is used in thermometers, mercury. X-ray examination of this black

174 metallic bond compound has shown it to be an intimate (or m-dinitrobenzene) is 1,3-dinitroben- mixture of mercury(II) oxide and mercury. zene. 2. Certain acids regarded as formed from mercury(II) oxide (mercuric oxide; HgO) an anhydride and water are named meta A poisonous compound formed as a yellow acids to distinguish them from the more powder by the addition of sodium(I) hy- hydrated ortho acids. For example, H2SiO3 droxide to a solution of mercury(II) nitrate (SiO2 + H2O) is metasilicic acid; H4SiO4 or as a red solid by heating mercury at (SiO2 + 2H2O) is orthosilicic acid. 350°C for a long time. The difference in See also ortho-; para-. color is simply one of particle size. If the oxide is strongly heated it decomposes to metabolism /mĕ-tab-ŏ-liz-ăm/ The bio- give mercury and oxygen. chemical reactions that take place in cells. The molecules taking part in these reac- mercury(I) sulfide (mercurous sulfide; tions are termed metabolites. Metabolic reactions characteristically occur in small Hg2S) The brownish black precipitate formed when mercury is treated with cold steps that together make up a metabolic concentrated sulfuric acid for a long time is pathway. They involve the breaking down thought to be mercury(I) sulfide. Alterna- of molecules to provide energy (catabo- tively it may be prepared by the action of lism) and the building up of more complex hydrogen sulfide or an alkaline sulfide on a molecules and structures from simpler mercury(I) salt solution. As soon as the molecules (anabolism). mercury(I) sulfide has been formed it dis- /mĕ-tab-ŏ-lÿt/ A substance proportionates to give mercury(II) sulfide metabolite that takes part in a metabolic reaction, ei- and mercury. ther as reactant or product. Some are synthesized within the organism itself, mercury(II) sulfide (mercuric sulfide; whereas others have to be taken in as food. vermilion; HgS) A compound that occurs in nature as the minerals cinnabar (a red metaiodic(VII) acid /met-ă-ÿ-od-ik/ See solid) and metacinnabar (a black solid). It iodic(VII) acid. is prepared as a black precipitate by the action of hydrogen sulfide on a soluble mer- metal See metals. cury(II) salt solution. On heating, mercury(II) sulfide sublimes and becomes metal carbonyl A coordination com- red. It is insoluble in dilute hydrochloric pound formed between a metal and car- and nitric acids but will dissolve in concen- bonyl groups. Transition metals form trated nitric acid and aqua regia. Mer- many such compounds. cury(II) sulfide is used as the pigment vermilion. metaldehyde /mĕ-tal-dĕ-hÿd/ See ethanal. meso-form /mess-oh-form/ See optical ac- metallic bond A bond formed between tivity. atoms of a metallic element in its zero oxidation state and in an array of similar mesomerism /mes-som-ĕ-riz-ăm/ See res- atoms. The outer electrons of each atom onance. are regarded as contributing to an ‘electron gas’, which occupies the whole crystal of meta- 1. Designating a benzene com- the metal. It is the attraction of the positive pound with substituents in the 1,3 posi- atomic cores for the negative electron gas tions. The position on a benzene ring that that provides the strength of the metallic is two carbon atoms away from a sub- bond. stituent is the meta position. This was used Quantum mechanical treatment of the in the systematic naming of benzene deriv- electron gas restricts its energy to a series of atives. For example, meta-dinitrobenzene ‘bands’. It is the behavior of electrons in

175 metallic crystal these bands that gives rise to semiconduc- everyday usage, metals are elements (and tors. alloys) such as iron, aluminum, and copper, which are lustrous malleable solids – metallic crystal A crystal formed by usually good conductors of heat and elec- metal atoms in the solid state. Each atom tricity. Note that this is not a strict defini- contributes its valence (outer) electrons to tion – some metals are poor conductors, a ‘sea’ of electrons, which are free to mi- mercury is a liquid, etc. grate through the solid, and the ions re- In chemistry, metals are distinguished maining are arranged in a lattice. The by their chemical properties, and there are ability of electrons to move through the lat- two main groups. Reactive metals, such as tice accounts for the electrical and thermal the alkali metals and alkaline-earth metals, conductivity of metals. are electropositive elements. They are high in the electromotive series and tend to form metallocene /mĕ-tal-ŏ-seen/ A sandwich compounds by losing electrons to give pos- compound in which a metal atom or ion is itive ions. They have basic oxides and hy- coordinated to two cyclopentadienyl ions. droxides. This typical metallic behavior Ferrocene (Fe(C5H5)2) is the commonest decreases across the periodic table and in- example. creases down a group in the table. The other type of metals are the transi- metalloid /met-ă-loid/ Any of a class of tion elements, which are less reactive, have chemical elements that are intermediate in variable valences, and tend to form com- properties between metals and non-metals. plexes. In the solid and liquid states metals Examples are germanium, arsenic, and tel- have metallic bonds, formed by positive lurium. ions with free electrons. See also metalloid; There is, in fact, no clear-cut distinction non-metal. between metals and non-metals. In the periodic table, there is a change from metallic metastable species /met-ă-stay-băl/ An to non-metallic properties across the table, excited state of an atom, ion, or molecule, and an increase in metallic properties that has a relatively long lifetime before re- down a group. Consequently there is a di- verting to the ground state. Metastable agonal around the center of the table (B, Si, species are intermediates in some reactions. As, Te) in which there is a borderline between metals and non-metals, and the met- metastable state A condition of a system alloids are the borderline cases. Elements or body in which it appears to be in stable such as arsenic, germanium, and tellurium equilibrium but, if disturbed, can settle are semiconductors, but other elements are into a lower energy state. For example, su- often said to be metalloids according to percooled water is liquid below 0°C (at their chemical properties. Tin, for instance, standard pressure). When a small crystal of forms salts with acids but also forms stan- ice or dust (for example) is introduced, nates with alkalis. Its oxide is amphoteric. rapid freezing occurs. Note also that tin has metallic (white tin) and non-metallic (gray tin) allotropes. metathesis /mĕ-tath-ĕ-sis/ See double decomposition. metalloporphyrin /mĕ-tal-oh-por-fă-rin/ See porphyrins. meter /mee-ter/ Symbol: m The SI base unit of length, defined as the distance trav- metallurgy /met-ă-ler-jee/ The study of eled by light in vacuum in 1/(2.99 792 458 metals, especially methods of extracting × 108) second. This definition was adopted metals from their ores and the formation in 1983 to replace the 1967 definition of a and properties of alloys. length equal to 1 650 763.73 wavelengths in vacuum corresponding to the transition metals Any of a class of chemical elements between the levels 2p10 and 5d5 of the 86Kr with certain characteristic properties. In atom.

176 methylbenzene methanal /meth-ă-nal/ (formaldehyde; sodium methanoate (NaOOCH). It is a HCOH) A colorless gaseous aldehyde. It is strong reducing agent. Methanoic acid oc- manufactured by the oxidation of curs naturally in ants and nettles. methanol (500°C and a silver catalyst): → 2CH3OH + O2 2HCOH + 2H2O methanol /meth-ă-nol, -nohl/ (methyl al- The compound is used in the manufacture cohol; wood alcohol; CH3OH) A colorless of urea–formaldehyde resins. A solution of liquid alcohol, which is used as a solvent methanal (40%) in water is called forma- and in the manufacture of methanal lin. It is extensively used as a preservative (formaldehyde) for the plastics and drugs for biological specimens. industries. Methanol was originally pro- If an aqueous solution of methanal is duced from the distillation of wood. Now evaporated a polymer – polymethanal – is it is manufactured by the catalytic oxida- formed: tion of methane from natural gas. –O–CH2–O–CH2–O–CH2– This was formerly called paraformalde- methionine /meth-ÿ-ŏ-neen, -nin/ See hyde. If methanal is distilled from acidic amino acids. solutions a cyclic methanal trimer (C3O3H6) is produced. methoxy group /meth-oks-ee/ The group CH3)–.

methyl acetate /meth-ăl/ See methyl ethanoate. CH2 O O methyl alcohol See methanol. methylamine /meth-ăl-ă-meen, -am-een/ H C CH (CH3NH2) A colorless flammable gas that 2 2 smells like ammonia. It is the simplest pri- O mary amine, used for making herbicides and other organic chemicals. Methanal trimer methylaniline /meth-ăl-an-ă-lin, -lÿn/ See toluidine. methane /meth-ayn/ (CH4) A gaseous alkane. Natural gas is about 99% methane methylated spirits /meth-ă-lay-tid/ and this provides an important starting Ethanol to which is added methanol (about material for the organic-chemicals indus- 9.5%), pyridine (about 0.5%), and a blue try. Methane can be chlorinated directly to dye. The ethanol is denatured in this way produce the more reactive chloromethanes, so that it can be sold without excise duty or it can be ‘reformed’ by partial oxidation for use as a fuel and solvent. or using steam to give mixtures of carbon oxides and hydrogen. Methane is the first methylation /meth-ă-lay-shŏn/ A reac- member of the homologous series of alka- tion in which a methyl group (CH3–) is in- nes. troduced in a compound. Friedel–Crafts reactions involving halo-methanes are ex- methanide /meth-ă-nÿd/ See carbide. amples of methylations. methanoate /meth-ă-noh-ayt/ (formate) A methylbenzene /meth-ăl-ben-zeen, -been- salt or ester of methanoic acid. zeen/ (toluene; C6H5CH3) A colorless liquid hydrocarbon, similar to benzene both methanoic acid /meth-ă-noh-ik/ (formic in structure and properties. As methylben- acid; HCOOH) A liquid carboxylic acid zene is much less toxic than benzene it is made by the action of sulfuric acid on more widely used, especially as a solvent.

177 methyl bromide

Large quantities are required for the man- range is clearly on the acid side, methyl or- ufacture of TNT (trinitrotoluene). ange is suitable for the titration of an acid Methylbenzene is itself produced either with a moderately weak base, such as from the fractional distillation of coal tar sodium carbonate. or from methylcyclohexane (a constituent of some crude oils): methylphenols /meth-ăl-fee-nol, -nohl/ → C6H11CH3 C6H5CH3 + 3H2 (cresols; HOC6H4CH3) Compounds with A catalyst of aluminum and molybdenum both methyl and hydroxyl groups substi- oxides is employed at high temperatures tuted onto the benzene ring. There are and pressures. three isomers, with the methyl group in the 2–, 3–, and 4– positions, respectively. A methyl bromide See bromomethane. mixture of the isomers can be obtained from coal tar. It is used as a germicide 2-methylbuta-1,3-diene (isoprene; (known as Lysol). CH2:CH(CH3)CH:CH2) A colorless unsaturated liquid hydrocarbon, which oc- methyl red An acid–base indicator that is curs in terpenes and natural rubber. It is red in solutions below a pH of 4.2 and yel- used to make synthetic rubber. low above a pH of 6.3. It is often used for the same types of titration as methyl or- methyl chloride See chloromethane. ange but the transition range of methyl red is nearer neutral (pH7) than that of methyl (acetonitrile; CH CN) A methyl cyanide 3 orange. The two molecules are structurally pleasant-smelling poisonous colorless li- similar. quid organic nitrile. Methyl cyanide is a polar solvent, and is widely used for dis- methyl salicylate (oil of wintergreen; solving both inorganic and organic com- methyl 2-hydroxybenzoate; C H O ) The pounds. 8 8 3 methyl ester of SALICYLIC ACID, which occurs in certain plants. It is absorbed methylene /meth-ă-leen/ See carbene. through the skin and used medicinally to methylene group The group :CH . relieve rheumatic symptoms. It is also used 2 in perfumes and as a flavoring agent in var- methyl ethanoate (methyl acetate; ious foods. CH3COOCH3) A colorless liquid ester with a fragrant odor. It is commonly used metric system A system of units based on as a solvent. the meter and the kilogram and using multiples and submultiples of 10. SI units, methyl ethyl ketone See butanone. c.g.s. units, and m.k.s. units are all scientific metric systems of units. methyl group The group CH3–. metric ton See tonne. methyl iodide See iodomethane. mho /moh/ See siemens. methyl methacrylate /meth-ak-ră-layt/ mÿ-kă (CH2:CCH3COOCH3) The methyl ester mica / / A member of an important of methacrylic acid. The compound is used group of aluminosilicate minerals that in the manufacture of a number of acrylic have a characteristic layered structure. The polymers, such as Plexiglas (polymethyl- three main types are biotite, lepidolite, and methacrylate). muscovite, which differ in their content of other elements (such as potassium, magne- methyl orange An acid–base indicator sium, and iron). Mica flakes are used as that is red in solutions below a pH of 3 and electrical insulators, dielectrics, and small yellow above a pH of 4.4. As the transition heat-proof windows.

178 mixture micelle /mi-sell/ An aggregate of mol- as if viewed in a mirror. If an object is not ecules in a COLLOID. symmetrical it cannot be superimposed on its mirror image. For example, the left micro- Symbol: µ A prefix denoting 10–6. hand is the mirror image of the right hand. For example, 1 micrometer (µm) = 10–6 meter (m). misch metal /mish/ A pyrophoric alloy of cerium and other lanthanoids, used in micron /mÿ-kron/ Symbol: µ A unit of lighter flints. length equal to 10–6 meter. miscible /miss-ă-băl/ Denoting combina- microwaves /mÿ-kroh-wayvz/ A form of tions of substances that, when mixed, give ELECTROMAGNETIC RADIATION, ranging in rise to only one phase; i.e. substances that wavelength from about 1 mm (where it dissolve in each other. See solid solution; merges with infrared) to about 120 mm solution. (bordering on radio waves). Microwaves are produced by various electronic devices Mitscherlich’s law /mich-er-lik/ (law of including the klyston; they are often car- isomorphism) The law stating that sub- ried over short distances in tubes of rectan- stances that crystallize in isomorphous gular section called waveguides. forms (i.e. have identical crystalline forms Spectra in the microwave region can and form mixed crystals) have similar give information on the rotational energy chemical compositions. The law can be levels of certain molecules. used to indicate the formulae of compounds. For instance, the fact that 1. The movement of an atom, migration chromium(III) oxide is isomorphous with group, or double bond from one position Fe O and Al O implies that its formula is to another in a molecule. 2 3 2 3 Cr O . The law is named for the German 2. The movement of ions in an electric 2 3 chemist Eilhard Mitscherlich (1794–1863). field. mixed indicator A mixture of two or milk of lime See calcium hydroxide. more indicators so as to decrease the pH range or heighten the color change, etc. milk sugar See lactose. milli- Symbol: m A prefix denoting 10–3. mixture Two or more substances forming For example, 1 millimeter (mm) = 10–3 a system in which there is no chemical meter (m). bonding between the two. In homogeneous mixtures (e.g. solutions or mixtures of millimeter of mercury See mmHg. gases) the molecules of the substances are mixed, and there is only one phase. In het- mineral A naturally occurring inorganic erogeneous mixtures (e.g. gunpowder or compound, usually crystalline and of defi- certain alloys) different phases can be dis- nite chemical composition; a mineral’s tinguished. Mixtures differ from chemical physical properties are also more or less compounds in that: constant. All rocks are composed of mix- 1. The chemical properties of the compo- tures of individual minerals. See rock. nents of a mixture are the same as those of the pure substances. mineral acid An inorganic acid, espe- 2. The mixture can be separated by physi- cially an acid used commercially in large cal means (e.g. distillation or crystalliza- quantities. Examples are hydrochloric, ni- tion) or mechanically. tric, and sulfuric acids. 3. The proportions of the components can vary. Some mixtures (e.g. certain solu- mirror image A shape that is identical to tions) can only vary in proportions be- another except that its structure is reversed tween definite limits.

179 m.k.s. system m.k.s. system A system of units based on mass of A grams (this mass was formerly the meter, the kilogram, and the second. It called one gram-atom of the element). formed the basis for SI units. molecular beam /mŏ-lek-yŭ-ler/ A beam mmHg (millimeter of mercury) A former of molecules (or atoms or ions) at low pres- unit of pressure defined as the pressure that sure such that the entities in the beam are will support a column of mercury one mil- moving in the same direction with few in- limeter high under specified conditions. It termolecular collisions. Molecular beams is equal to 133.322 4 Pa, and is almost are used in spectroscopy and in the study of identical to the torr. intermolecular forces, chemical reactions, and surfaces. mobile phase See chromatography. molecular crystal /mŏ-lek-yŭ-ler/ A crys- moiety /moi-ĕ-tee/ A distinct part of a tal in which molecules, as opposed to molecule; for example, the sugar moiety in atoms, occupy lattice points. Examples in- a nucleoside. clude iodine and solid carbon dioxide (dry ice). Because the forces holding the mole- molal concentration /moh-lăl/ See con- cules together are weak, molecular crystals centration. have low melting points. When the molecules are small, the crystal structure ap- molar /moh-ler/ 1. Denoting a physical proximates to a close-packed arrangement. quantity divided by the amount of sub- See close packing. stance. In almost all cases the amount of substance will be in moles. For example, molecular formula The formula of a compound showing the number and types volume (V) divided by the number of moles of the atoms present in a molecule, but not (n) is molar volume V = v/n. m the arrangement of the atoms. For exam- 2. A molar solution contains one mole of ple, C H O represents the molecular for- solute per cubic decimeter of solvent. 2 6 mula both of ethanol (C2H5OH) and methoxymethane (CH OCH ). The molec- molarity /moh-la-ră-tee/ A measure of the 3 3 ular formula can be determined only if the concentration of solutions based upon the molecular weight is known. Compare em- number of molecules or ions present, pirical formula; general formula; structural rather than on the mass of solute, in any formula. particular volume of solution. The molarity (M) is the number of moles of solute in molecularity /mŏ-lek-yŭ-la-ră-tee/ The one cubic decimeter (litre). Thus a 0.5M total number of reacting molecules in the solution of hydrochloric acid contains 0.5 individual steps of a chemical reaction. × 3 (1 + 35.5)g HCl per dm of solution. Thus, a unimolecular step has molecularity 1, a bimolecular step 2, etc. Molecularity is mole Symbol: mol The SI base unit of always an integer, whereas the order of a amount of substance, defined as the reaction need not necessarily be so. The amount of substance that contains as many molecularity of a reaction gives no infor- elementary entities as there are atoms in mation about the mechanism by which it 0.012 kilogram of 12C. The elementary en- takes place. tities may be atoms, molecules, ions, electrons, photons, etc., and they must be molecular orbital See orbital. specified. The amount of substance is proportional to the number of entities, the molecular sieve A substance through constant of proportionality being the Avo- which molecules of a limited range of sizes gadro number. One mole contains can pass, enabling volatile mixtures to be 6.022 045 × 1023 entities. One mole of an separated. Zeolites and other metal alu- element with relative atomic mass A has a minum silicates can be manufactured with

180 monosodium glutamate pores of constant dimensions in their mol- molybdenite (MoS2) and wulfenite ecular structure. When a sample is passed (PbMoO4). It is used in alloy steels, lamp through a column packed with granules of bulbs, and catalysts. The compound am- this material, some of the molecules enter monium molybdate, dissolved in nitric these pores and become trapped. The re- acid, is used as a test for phosphates(V). mainder of the mixture passes through the Molybdenum sulfide (MoS2) is used in lu- interstices in the column. The trapped mol- bricants to enhance viscosity. ecules can be recovered by heating. Molec- Symbol: Mo; m.p. 2620°C; b.p. ular-sieve chromatography is widely used 4610°C; r.d. 10.22 (20°C); p.n. 42; r.a.m. in chemistry and biochemistry laborato- 95.94. ries. A modified form of molecular sieve is used in gel filtration. The sieve is a contin- monatomic /mon-ă-tom-ik/ Denoting a uous gel made from a polysaccharide. In molecule, radical, or ion consisting of only this case, molecules larger than the largest one atom. For example, helium is a pore size are totally excluded from the col- monatomic gas and H• is a monatomic umn. radical. molecular spectrum The absorption or Mond process /mohnt/ See nickel. emission spectrum that is characteristic of a molecule. Molecular spectra are usually monobasic acid /mon-oh-bay-sik/ An band spectra. acid that has only one active proton, such as hydrochloric acid. See also dibasic acid. molecular weight See relative molecular mass. monochlorobenzene /mon-ŏ-klor-oh- ben-zeen, -klor-oh-ben-zeen, -kloh-roh-/ molecule /mol-ĕ-kyool/ A particle formed See chlorobenzene. by the combination of atoms in a whole- number ratio. A molecule of an element monoclinic crystal /mon-ŏ-klin-ik/ See (combining atoms are the same, e.g. O2) or crystal system. of a compound (different combining atoms, e.g. HCl) retains the properties of monohydrate /mon-ŏ-hÿ-drayt/ A salt that element or compound. Thus, any that has a single molecule of WATER OF quantity of a compound is a collection of CRYSTALLIZATION, such as sodium carbon- many identical molecules. Molecular sizes ate monohydrate, Na2CO3.H2O. are characteristically 10–10 to 10–9 m. Many molecules of natural products are monohydric alcohol /mon-ŏ-hÿ-drik/ so large that they are regarded as giant See alcohol. molecules (macromolecules); they may contain thousands of atoms and have com- monomer /mon-ŏ-mer/ The molecule, plex structural formulae that require very group, (or compound) from which a dimer, advanced techniques to identify. See also trimer, or POLYMER is formed. formula; relative molecular mass. monosaccharide /mon-ŏ-sak-ă-rÿd, -rid/ mole fraction The number of moles of a A sugar that cannot be hydrolyzed to sim- given component in a mixture divided by pler carbohydrates of smaller carbon con- the total number of moles present of all the tent. Glucose and fructose are examples. components. The mole fraction of component A is monosodium glutamate /mon-ŏ-soh- nA/(nA + nB + nC + …) dee-ŭm gloo-tă-mayt/ (MSG) A white crys- where nA is the number of moles of A, etc. talline solid compound, made from soya-bean protein. It is a sodium salt of molybdenum /mŏ-lib-dĕ-nŭm/ A transi- glutamic acid (see amino acid) used as a tion element that occurs naturally in flavor enhancer, particularly in Chinese

181 monoterpene cuisine. Monosodium glutamate can cause multidecker sandwich compound See an allergic reaction in people who are ul- sandwich compound. trasensitive to it. multidentate ligand /mul-ti-den-tayt/ A monoterpene See terpene. ligand that possesses at least two sites at which it can coordinate. monotropy /mŏ-not-rŏ-pee/ The existence of a single allotrope of an element multiple bond A bond between two that is always more stable than the other(s) atoms involving more than one pair of elec- regardless of temperature; phosphorus, for trons, e.g. a double bond or a triple bond. example, exhibits monotropy. The phase This additional bonding arises from over- diagram for a monotropic element shows lap of atomic orbitals that are perpendicu- that one allotrope always has a lower lar to the inter-nuclear axis and gives rise vapor pressure than the other(s) at all tem- to an increase in electron density above and peratures; this is the stable allotrope. below the inter-nuclear axis. Such bonds are called pi bonds. If the sigma bond axis monovalent /mon-ŏ-vay-lĕnt, mŏ-nov-ă-/ is taken as the z-axis (i.e. the inter-nuclear (univalent) Having a valence of one. axis) then overlap of orbitals along the x- axis gives rise to a pi bond in the xz plane. mordant /mor-dănt/ An inorganic com- Similarly orbitals on the y-axis form a pi pound used to fix dye in cloth. The mor- bond in the yz plane. dant (e.g. aluminum hydroxide or chromium salts) is precipitated in the fibers multiple proportions, law of Proposed of the cloth, and the dye then absorbs in by Dalton in 1804, the principle that when the particles. two elements A and B combine to form more than one compound, the weights of B Moseley’s law Lines in the x-ray spectra that combine with a fixed weight of A are of elements have frequencies that depend in small whole-number ratios. For exam- on the proton number of the element. For ple, in dinitrogen oxide, N O, nitrogen a set of elements, a graph of the square root 2 of the frequency of x-ray emission against monoxide, NO, and dinitrogen tetroxide, proton number is a straight line (for spec- N2O4, the amounts of nitrogen combined tral lines corresponding to the same transi- with a fixed weight of oxygen are in the tion). The law is named for the British ratio 4:2:1. physicist Henry Gwyn Jeffreys Moseley (1887–1915). multiple-range indicator See universal indicator. mother liquor The solution remaining after the formation of crystals. Mumetal /myoo-met-ăl/ (Trademark) A magnetic alloy containing about 75% MSG See monosodium glutamate. nickel, the remainder being iron, copper, and chromium and sometimes molybde- multicenter bond /mul-ti-sen-trik/ A num. It is easily magnetized and demagne- two-electron bond formed by the overlap tized, has a high permeability, and is used of orbitals from more than two atoms (usu- in transformer cores and electromechanical ally 3). The bridging in diborane is believed equipment. to take place by overlap of an sp3 hybrid orbital from each boron atom with the 1s muriate /myoor-ee-ayt/ An obsolete name orbital on the hydrogen atom. This multi- for a chloride; e.g. muriate of potash (KCl). center bond is called a two-electron three- center bond. The molecule is mustard gas (2,2′-dichlorodiethyl sulfide; electron-deficient. See also electron-defi- ((CH2ClCH2)2S) A poisonous vesicant gas cient compounds. used as a war gas.

182 myoglobin mutarotation /myoo-tă-roh-tay-shŏn/ A myoglobin /mÿ-oh-gloh-bin/ A globular change in the optical rotation of a solution protein formed of a heme group and a sin- with time, as when one optical isomer dis- gle polypeptide chain. It occurs in muscle appears and another is formed. tissue where it acts as an oxygen store.

183 N

nano- Symbol: n A prefix denoting 10–9. and thence in the production of plastics For example, 1 nanometer (nm) = 10–9 and dyes. meter (m). The structure of naphthalene is ‘benzene-like’, having two six-membered rings nanotechnology /nan-oh-tek-nol-ŏ-jee/ fused together. The reactions are charac- The technology of devices at the nanome- teristic of AROMATIC COMPOUNDS. ter scale. In such small devices the quantum mechanical nature of electrons has to be taken into account fully. Instruments such as the ATOMIC FORCE MICROSCOPE which can identify and manipulate individual atoms are very useful in nanotechnology. nanotubes /nan-ŏ-tewbz/ Tubular structures with diameters of a few nanometers (1nm = 10–9 m). Examples of nanotubes are the carbon structures known as ‘bucky tubes’, which have a structure similar to that of BUCKMINSTERFULLERENE. Interest has been shown in nanotubes as possible microscopic probes in experiments, as semiconductor materials, and as a component of composite materials. Nanotubes can also be produced by joining amino acids to give tubular polypeptide struc- Representations of naphthalene tures. naphtha /naf-thă, nap-thă/ (solvent naph- nascent hydrogen /nay-sĕnt/ A particu- tha) An imprecise term for a mixture of larly reactive form of hydrogen, which is hydrocarbons obtained from coal and pe- believed to exist briefly between its genera- troleum. It has a boiling range of tion (e.g. by the action of dilute acid on 70–160°C and is used as a solvent and as a magnesium) and its appearance as bubbles raw material for making various other or- of normal hydrogen gas. It is thought that ganic chemicals. part of the free energy of the production reaction remains with the hydrogen mol- naphthalene /naf-thă-leen, nap-thă-leen/ ecules for a short time. Nascent hydrogen (C10H8) A white crystalline solid with a may be used to produce the hydrides of distinctive smell of mothballs. Naphtha- phosphorus, arsenic, and antimony, which lene is found in both the middle- and are not readily formed from ordinary hy- heavy-oil fractions of crude oil and is ob- drogen. tained by fractional crystallization. It is used in the manufacture of benzene-1,2-di- natron /nay-tron/ A naturally occurring carboxylic anhydride (phthalic anhydride) form of hydrated SODIUM CARBONATE

184 neutron number

(Na2CO3.10H2O), found on the beds of It is more resistant to oil, solvents, and dried-out soda lakes. temperature than natural rubbers.

Natta process /nat-ă/ A method for the neptunium /nep-tew-nee-ŭm/ A toxic ra- manufacture of isotactic polypropene dioactive silvery element of the actinoid se- using Ziegler catalysts. The process is ries of metals that was the first transuranic named for the Italian chemist Giulio Natta element to be synthesized (1940). Found (1903–79). See also addition polymeriza- on Earth only in minute quantities in ura- tion; Ziegler process. nium ores, it is obtained as a by-product from uranium fuel elements. natural abundance See abundance. Symbol: Np; m.p. 640°C; b.p. 3902°C; r.d. 20.25 (20°C); p.n. 93; most stable iso- natural gas Gas obtained from under- tope 237Np (half-life 2.14 × 106 years). ground deposits and often associated with sources of petroleum. It contains a high neutralization The stoichiometric reac- proportion of methane and other volatile tion of an acid and a base in volumetric hydrocarbons. analysis. The neutralization point or end point is detected with indicators. neighboring-group participation An effect in an organic reaction in which neutral oxide An oxide that forms nei- groups close to the point at which reaction ther an acid nor a base on reaction with occurs affect the rate of reaction or stereo- water. Examples include carbon monoxide chemistry of the products in some way. (CO), dinitrogen oxide (N2O), and water (H2O). See acidic oxide; amphoteric; basic nematic crystal /ni-mat-ik/ See liquid oxide. crystal. neutron diffraction A method of struc- neodymium /nee-ŏ-dim-ee-ŭm/ A toxic ture determination that makes use of the silvery element belonging to the lanthanoid quantum mechanical wave nature of neu- series of metals. It occurs in association trons. Thermal neutrons with average ki- with other lanthanoids. Neodymium is netic energies of about 0.025 eV have a used in various alloys, as a catalyst, in com- wavelength of about 0.1 nanometer, mak- pound form in carbon-arc searchlights, ing them suitable for investigating the etc., and in the glass industry. structure of matter at the atomic level. Symbol: Nd; m.p. 1021°C; b.p. Neutron diffraction is particularly useful 3068°C; r.d. 7.0 (20°C); p.n. 60; r.a.m. for identifying the positions of hydrogen 144.24. atoms. These are difficult to establish using x-rays since x-rays interact with electrons, neon /nee-on/ An inert colorless odorless and hence are scattered weakly by hydro- monatomic element of the rare-gas group. gen atoms, which have only one electron. Neon forms no compounds. It occurs in Protons scatter neutrons strongly, meaning minute quantities (0.0018% by volume) in that the positions of protons can readily be air and is obtained from liquid air. It is determined using neutron scattering. Neu- used in neon signs and lights, electrical tron diffraction has also been used in in- equipment, and gas lasers. vestigations of the magnetic ordering in Symbol: Ne; m.p. –248.67°C; b.p. solids because there is an interaction be- –246.05°C; d. 0.9 kg m–3 (0°C); p.n. 10; tween the magnetic moments of the neu- r.a.m. 20.18. trons and the magnetic moments of atoms in the sample. neoprene /nee-ŏ-preen/ A type of synthetic rubber made by polymerization of 2- neutron number Symbol: N The number chlorobuta-1,2,-diene (H2C:CHCCl:CH2). of neutrons in the nucleus of an atom; i.e. 185 Newlands’ law the nucleon number (A) minus the proton bon monoxide over finely divided nickel at number (Z). a temperature of approximately 60°C. The product is purified by fractional distilla- Newlands’ law (law of octaves) The ob- tion. Nickel carbonyl decomposes on heat- servation that, when the elements are ing to give pure nickel. It is used as a arranged in order of increasing relative catalyst and in the preparation of nickel atomic mass (atomic weight), there is a (Mond process). similarity between members that are eight elements apart (inclusive). For example, nickelic oxide See nickel(III) oxide. lithium has similarities to sodium, beryllium to magnesium, and so on. Newlands nickel–iron accumulator (Edison cell; discovered this relationship in 1863 before Nife or NIFE cell) A type of secondary cell the announcement of Mendeléev’s famous in which the electrodes are formed by steel periodic law (1869). It is now recognized grids. The positive electrode is impreg- that Newlands’ law arises from there being nated with a nickel–nickel hydride mixture eight members in each short period. The and the negative electrode is impregnated law is named for the British chemist John with iron oxide. Potassium hydroxide solu- Alexander Reina Newlands (1837–98). tion forms the electrolyte. The nickel–iron cell is lighter and more durable than the newton Symbol: N The SI unit of force, lead accumulator, and it can work with equal to the force needed to accelerate one higher currents. Its e.m.f. is approximately kilogram by one meter second–2. 1 N = 1 kg 1.3 volts. The cell is also named for the m s–2. The unit is named for the English American physicist and inventor Thomas physicist and mathematician Sir Isaac Alva Edison (1847–1931). Newton (1642–1727). nickelous oxide See nickel(II) oxide. Nichrome /nÿ-krohm/ (Trademark) Any of a group of nickel–chromium–iron al- nickel(II) oxide (nickelous oxide; NiO) loys, containing 60–80% nickel and about A pale green powder formed by heating 16% chromium; small amounts of other el- nickel(II) hydroxide, nitrate, or carbonate ements, such as carbon or silicon, may be in the absence of air. It is a basic oxide dis- added. They can withstand very high tem- solving in dilute acids to give green solu- peratures and their high electrical resistiv- tions of nickel(II) salts. Nickel(II) oxide ity makes them suitable for use in heating may be reduced by carbon, carbon monox- elements. ide, or hydrogen. nickel /nik-ăl/ A transition metal that oc- nickel(III) oxide (nickelic oxide; Ni2O3) curs naturally as the sulfide and silicate. It A black powder formed by the action of is extracted by the Mond process, which in- heat on nickel(II) oxide in air. It can also be volves reduction of nickel oxide using car- prepared by igniting nickel(II) nitrate or bon monoxide followed by the formation carbonate. It exists as the dihydrate, and subsequent decomposition of volatile Ni2O3.2H2O. nickel carbonyl. Nickel is used as a catalyst in the hydrogenation of alkenes, e.g. mar- nickel-silver (German silver) Any of a garine manufacture, and in coinage alloys. group of alloys containing nickel, copper, Its main oxidation state is +2 and these and zinc in various proportions (but no sil- compounds are usually green. ver). They are white or silvery in color, can Symbol: Ni; m.p. 1453°C; b.p. 2732°C; be highly polished, and have good corro- r.d. 8.902 (25°C); p.n. 28; r.a.m. 58.6934. sion-resistance. They are used, for example, in silver plating, chromium plating, nickel carbonyl (tetracarbonyl nickel(0); and enameling. Ni(CO)4) A colorless liquid with a highly toxic vapor. It is prepared by passing car- nielsbohrium /neels-bor-ee-ŭm/ Symbol:

186 nitro compound

Ns A name formerly suggested for ele- rus) react to produce oxyacids. Organic ment-107 (bohrium). See element. substances (e.g. sawdust and ethanol) react violently, but the more stable aromatic NIFE cell See nickel–iron accumulator. compounds, such as benzene and toluene, can be converted to nitro compounds in ninhydrin /nin-hÿ-drin/ A colorless or- controllable reactions. ganic compound that gives a blue coloration with amino acids. It is used as a test nitric oxide See nitrogen monoxide. for amino acids, in particular to show the positions of spots of amino acids in paper nitride /nÿ-trÿd/ A compound of nitrogen chromatography. with a more electropositive element such as magnesium or calcium. niobium /nÿ-oh-bee-ŭm/ A soft silvery transition element used in welding, special nitriding /nÿ-trÿ-ding/ See case hardening. steels, and nuclear reactor work. Symbol: Nb; m.p. 2468°C; b.p. nitrification /ny-tră-fă-kay-shŏn/ The ac- 4742°C; r.d. 8.570 (20°C); p.n. 41; r.a.m. tion of nitrifying bacteria in converting 92.90638. ammonia and nitrites to nitrates. It is an important stage in the NITROGEN CYCLE. See niter /nÿ-ter/ See potassium nitrate. also nitrogen fixation. nitrate /nÿ-trayt/ A salt or ester of nitric nitrile /nÿ-trăl, -tril, -trÿl/ (cyanide) A type acid. of organic compound containing the –CN group. Nitriles are colorless liquids with nitration /nÿ-tray-shŏn/ A reaction intro- pleasant smells. They can be prepared by ducing the nitro (–NO2) group into an or- either refluxing an organic halogen com- ganic compound. Nitration of aromatic pound with an alcoholic solution of potas- compounds is usually carried out using a sium cyanide, or by dehydration of an mixture of concentrated nitric and sulfuric amide with phosphorus(V) oxide. Charac- acids, although the precise conditions dif- teristic reactions are hydrolysis (to the car- fer from compound to compound. The at- boxylic acid and ammonia) and reduction + tacking species is NO2 (the nitryl cation), with hydrogen gas (to an amine). and the reaction is an example of electrophilic substitution. nitrile rubber A copolymer of butadiene and propenonitrile (acrylonitrile) nitric acid /nÿ-trik/ (HNO3) A colorless (CH2=CHCN). It is an important rubber fuming corrosive liquid that is a strong due to its resistance to oil and solvents. acid. Nitric acid can be made in a laboratory by the distillation of a mixture of an nitrite /nÿ-trÿt/ A salt or ester of nitrous alkali metal nitrate and concentrated sulfu- acid. ric acid. Commercially it is prepared by the catalytic oxidation of ammonia and is sup- nitrobenzene /nÿ-troh-ben-zeen, -ben- plied as concentrated nitric acid, which zeen/ (C6H5NO2) A yellow organic oil ob- contains 68% of the acid and is often col- tained by refluxing benzene with a mixture ored yellow by dissolved oxides of nitro- of concentrated nitric and sulfuric acids. gen. The reaction is a typical electrophilic sub- Nitric acid is a strong oxidizing agent. stitution on the benzene ring by the nitryl + Most metals are converted to their nitrates cation (NO2 ). with the evolution of oxides of nitrogen (the composition of the mixture of the ox- nitrocellulose /nÿ-troh-sell-yŭ-lohs/ See ides depends on the temperature and on the cellulose trinitrate. concentration of the nitric acid used). Some non-metals (e.g. sulfur and phospho- nitro compound /nÿ-troh/ A type of or-

187 nitrogen

Nitrogen forms a number of oxides: O 1. Dinitrogen monoxide (nitrous oxide, N2O) – a neutral oxide. N 2. Nitrogen monoxide (nitric oxide, NO) – O a neutral oxide. 3. Nitrogen(III) oxide (nitrogen sesquioxide, N2O3) – an unstable oxide that is Nitro compound the anhydride of nitrous acid. 4. dioxide (NO2), which gives a mixture of ganic compound containing the nitro nitrous and nitric acids in water. (–NO ) group attached to an aromatic 2 5. Dinitrogen tetroxide (N2O4), which is in ring. Nitro compounds can be prepared by equilibrium with nitrogen dioxide. nitration using a mixture of concentrated 6. Dinitrogen pentoxide (N2O5) – the an- nitric and sulfuric acids. They can be re- hydride of nitric acid. duced to aromatic amines: 7. Nitrogen trioxide (NO ). → 3 RNO2 + 3H2 RNH2 + 2H2O Nitrogen also forms a number of binary They can also undergo further substitution halides such as NF3, NCl3, and halogen on the benzene ring. The nitro group di- azides such as ClN . Except for NF these rects substituents into the 3 position. 3 3 are all very explosive, and even NF3, which is reputedly stable, has been known to ex- nÿ-trŏ-jĕn nitrogen / / The first element of plode. group 15 of the periodic table; a very elec- Transition metals form nitrides that are tronegative element existing in the uncom- different from the ionic or covalent ni- bined state as gaseous diatomic N 2 trides, the stoichiometries are, for example, molecules. The nitrogen atom has the elec- ZrN, W N, Mn N. They are often called tronic configuration [He]2s22p3. It is typi- 2 4 ‘interstitial’ nitrides. They are very hard cally non-metallic and its bonding is and their formation is the basis of surface primarily by polarized covalent bonds. hardening by exposing hot metal to ammo- With electropositive elements the nitride nia gas (see case hardening). ion N3– may be formed. Nitrogen has two isotopes; 14N, the Nitrogen accounts for about 78% of 15 the atmosphere (by volume) and it also oc- common isotope, and N (natural abun- curs as sodium nitrate in various mineral dance 0.366%), which is used as a marker deposits. It is separated for industrial use in mass spectrometric studies. ° by the fractionation of liquid air. Pure ni- Symbol: N; m.p. –209.86 C; b.p. ° –3 ° trogen is prepared by thermal decomposi- –195.8 C; d. 1.2506 kg m (0 C); p.n. 7; tion of azides; r.a.m. 14. → 2NaN3 2Na + 3N2 The ‘active nitrogen’ gas obtained by nitrogen cycle The circulation of nitro- passing an electric discharge through nitrogen and its compounds in the environment, gen is a mixture of ordinary nitrogen mol- one of the major natural cycles of an ele- ecules and excited single nitrogen atoms. ment. Nitrogen occurs mainly as a gas in Nitrogen is a diatomic molecule, which the atmosphere and as nitrates in the soil. is effectively triple-bonded and has a high Denitrification of these nitrates converts dissociation energy (940 kJ mol–1). It is them to nitrogen. Plants also take up ni- therefore inert and it only reacts readily trates and are eaten by animals; the plants with lithium and other highly electroposi- and animals convert them to proteins, tive elements. The direct combination of which after the death of the organisms ap- nitrogen and hydrogen occurs at elevated pears as ammonia, which nitrification con- temperatures and pressures (400–600°C, verts back to nitrates. Fixation of 100 atmospheres) and is the basis of the in- atmospheric nitrogen by bacteria or light- dustrially important Haber process for the ning also gives rise to nitrates. See also ni- manufacture of ammonia. trification; nitrogen fixation.

188 nitrous acid nitrogen dioxide /dÿ-oks-ÿd, -id/ (NO2) tures it combines immediately with oxygen A brown gas produced by the dissociation to give nitrogen dioxide: → of dinitrogen tetroxide (with which it is in 2NO(g) + O2(g) 2NO2(g) equilibrium), the dissociation being complete at 140°C. Further heating causes dis- nitrogenous base /nÿ-troj-ĕ-nŭs/ See qua- sociation to colorless nitrogen monoxide ternary ammonium compound. and oxygen: 2NO2(g) = 2NO(g) + O2(g) nitrogen oxides Any of the various com- Nitrogen dioxide can also be made by pounds formed between nitrogen and oxy- the action of heat on metal nitrates (not the gen. See dinitrogen oxide; nitrogen; nitrates of the alkali metals or some of the nitrogen dioxide; nitrogen monoxide. alkaline-earth metals). nitroglycerine /nÿ-troh-gliss-ĕ-rin, -reen/ nitrogen fixation A reaction in which at- (glyceryl trinitrate) A highly explosive sub- mospheric nitrogen is converted into nitro- stance used in dynamite. It is obtained by gen compounds. Nitrogen fixation occurs treating glycerol (1,2,3-trihydroxy- naturally by certain bacteria (in the soil propane) with a mixture of concentrated and in the roots of leguminous plants). nitric and sulfuric acids. It is not a nitro Small amounts of nitrogen(II) oxide (NO) compound, but a nitrate ester are also formed in thunderstorms by direct CH2(NO3)CH(NO3)CH2(NO3) combination of the elements in the electrical discharge. Fixation of nitrogen is im- nitro group The group –NO2; the functional group of nitro compounds. portant because nitrogen is an essential element for plant growth, and vast nitro ligand See isomerism. amounts of nitrogenous fertilizers are also required for agriculture. Former processes nitronium ion /nÿ-troh-nee-ŭm/ See nitryl for fixing nitrogen were the Birkeland- ion. Eyde process (reacting N2 and O2 in an electric arc – the equivalent of the thunder- nitrophenols /nÿ-troh-fee-nolz, -nohlz/ storm in nature), and the cyanamide (C6H4(OH)NO2) Organic compounds process (heating calcium dicarbide with ni- formed directly or indirectly by the nitra- trogen to give CaCN2). Now the major tion of phenol. Three isomeric forms are method is the Haber process for making possible. The 2 and 4 isomers are produced ammonia. by the direct nitration of phenol and can be separated by steam distillation, the 2 iso- nitrogen monoxide /mon-oks-ÿd, -id/ (ni- mer being steam volatile. The 3 isomer is tric oxide; NO) A colorless gas that is in- produced from nitrobenzene by formation soluble in water but dissolves in a solution of 1,3-dinitrobenzene, conversion to 3-ni- containing iron(II) ions owing to the for- trophenylamine, and thence by diazotiza- 2+ mation of the complex ion (FeNO) : the tion to 3-nitrophenol. nitrogen monoxide can be released by heating. Nitrogen monoxide is prepared by nitroso ligand See isomerism. the action of nitric acid on copper turnings; the impure product can be purified by nitrous acid /nÿ-trŭs/ (HNO2) A weak using a solution of iron(II) ions to absorb acid known only in solution, obtained by the product. Commercially, nitrogen acidifying a solution of a nitrite. It readily monoxide is prepared by the catalytic oxi- decomposes on warming or shaking to ni- dation of ammonia or by the direct union trogen monoxide and nitric acid. The use of nitrogen and oxygen in an electric arc. of nitrous acid is very important in the Nitrogen monoxide is the most heat-stable dyestuffs industry in the diazo reaction: ni- of the oxides of nitrogen, only decompos- trous acid is liberated by acidifying a solu- ing above 1000°C. At ordinary tempera- tion of a nitrite (usually sodium nitrite) in

189 nitrous oxide the presence of the compound to be diazo- nonstoichiometric compound A chem- tized. Nitrous acid and the nitrites are nor- ical compound whose molecules contain mally reducing agents but in certain fractional numbers of atoms. For example, circumstances they can behave as oxidizing titanium(IV) oxide in the form of the min- agents, e.g. with sulfur dioxide and hydro- eral rutile has the chemical formula TiO1.8. gen sulfide. normality The number of gram equiva- nitrous oxide See dinitrogen oxide. lents per cubic decimeter of a given solution. nitryl ion /nÿ-trăl/ (nitronium ion) The + A solution that contains positive ion NO2 . See nitration. normal solution one gram equivalent weight per liter of so- NMR See nuclear magnetic resonance. lution. Values are designated by the symbol N, e.g. 0.2N, N/10, etc. Because there nobelium /noh-bel-ee-ŭm/ A radioactive is not a clear definition of equivalent transuranic element of the actinoid series, weight suitable for all reactions, a solution not found naturally on Earth. Several very may have one value of normality for one short-lived isotopes have been synthesized. reaction and another value in a different re- Symbol: No; p.n. 102; most stable iso- action. Because of this many workers pre- tope 259No (half-life 58 minutes). fer the molar solution notation. noble gases See rare gases. NTP See STP. (NMR) A nonbenzenoid aromatic /non-ben-zĕ- nuclear magnetic resonance method of investigating nuclear spin. In an noid/ See aromatic compound. external magnetic field the nucleus can have certain quantized energy states, corre- nonessential amino acid See amino sponding to certain orientations of the spin acid. magnetic moment. Hydrogen nuclei, for instance, can have two energy states, and nonionic detergent /non-ÿ-on-ik/ See de- transitions between the two occur by ab- tergents. sorption of radiofrequency radiation. In chemistry, this is the basis of a spectro- nonlocalized bond See delocalized bond. scopic technique for investigating the structure of molecules. Radiofrequency ra- nonmetal Any of a class of chemical ele- diation is fed to a sample and the magnetic ments. Non-metals lie in the top right-hand field is changed slowly. Absorption of the region of the periodic table. They are elec- radiation is detected when the difference tronegative elements with a tendency to between the nuclear levels corresponds to form covalent compounds or negative ions. absorption of a quantum of radiation. This They have acidic oxides and hydroxides. In difference depends slightly on the electrons the solid state, nonmetals are either cova- around the nucleus – i.e. the position of the lent volatile crystals or macromolecular atom in the molecule. Thus a different ab- (giant-covalent) crystals. See also metal; sorption frequency is seen for each type of metalloid. hydrogen atom (this is an example of a chemical shift). In ethanol, for example, nonpolar compound A compound that there are three frequencies, corresponding has molecules with no permanent dipole to hydrogen atoms on the CH3, the CH2, moment. Examples of non-polar com- and the OH. The intensity of absorption pounds are hydrogen, tetrachloromethane, also depends on the number of hydrogen and carbon dioxide. atoms (3:2:1). NMR spectroscopy is a powerful method of finding the structures nonpolar solvent See solvent. of organic compounds.

190 nucleophilic substitution nuclear magneton See magneton. larly water. The addition of hydrogen cyanide to propanone is an example: → nucleic acids Organic acids whose mol- CH3COCH3 + HCN ecules consist of chains of alternating sugar CH3C(CN)(OH)CH3 and phosphate units, with nitrogenous See also condensation reaction. bases attached to the sugar units. They occur in the cells of all organisms. In DNA nucleophilic reagent A compound that the sugar is deoxyribose; in RNA it is ri- contains electron-rich groups of atoms that bose. See DNA; RNA. can donate electrons during a chemical reaction. They are generally oxidizing nucleon number (mass number) Symbol: agents. See oxidation. A The number of nucleons (protons plus neutrons) in an atomic nucleus. nucleophilic substitution A reaction involving the substitution of an atom or nucleophile /new-klee-ŏ-fÿl/ An electron- group of atoms in an organic compound rich ion or molecule that takes part in an with a nucleophile as the attacking sub- organic reaction. The nucleophile can be a stituent. Since nucleophiles are electron- negative ion (Br–, CN–) or a molecule with rich species, nucleophilic substitution a lone pair of electrons (NH3, H2O). The occurs in compounds in which a strongly nucleophile attacks positively charged electronegative atom or group leads to a parts of molecules, which usually arise dipolar bond. The electron-deficient center from the presence of an electronegative can then be attacked by the electron-rich atom elsewhere in the molecule. Compare nucleophile causing the electronegative electrophile. atom or group to be displaced. In general terms: nucleophilic addition /new-klee-ŏ-fil-ik/ R–Le + Nu– → R–Nu + Le– A class of reaction involving the addition where Nu– represents the incoming nucle- of a small molecule to the double bond in ophile and Le– represents the leaving an unsaturated organic compound. Since group. these reactions are initiated by nucle- There are two possible mechanisms for ophiles, the unsaturated bond must con- nucleophilic substitution. In a SN1 reaction tain an electronegative atom, which creates the molecule first forms a carbonium ion; an electron-deficient area in the molecule. for example: → + – Nucleophilic addition is a characteristic re- RCH2Cl RCH2 + Cl action of aldehydes and ketones and is The nucleophile then attaches itself to this often followed by the subsequent elimina- carbonium ion: + – → tion of a different small molecule, particu- RCH2 + OH RCH2OH

X X + – CCl C +Cl Y ZYZ

OH– OH–

X X COH HO C Y Y Z Z

Nucleophilic substitution: the SN1 reaction

191 nucleoside

X X – OH– C Cl HO... C ... Cl Y ZYZ

X HO C +Cl– Y Z

Nucleophilic substitution: the SN2 reaction

In a SN2 reaction the nucleophile ap- uses) The compact positively charged cen- proaches as the other group leaves, form- ter of an atom made up of one or more nu- ing a transition state in which the carbon cleons (protons and neutrons) around has five attached groups. which is a cloud of electrons. The density The preferred mechanism depends on of nuclei is about 1015 kg m–3. The number several factors: of protons in the nucleus defines the ele- 1. The stability of the intermediate in the ment, being its proton number (or atomic SN1 mechanism. number). The nucleon number, or atomic 2. Steric factors affecting the formation of mass number, is the sum of the protons and the transition state in the SN2 mecha- neutrons. The simplest nucleus is that of a nism. hydrogen atom, 1H, being simply one pro- 3. The solvent in which the reaction oc- ton (mass 1.67 × 10–27 kg). The most mas- curs: polar solvents will stabilize polar sive naturally occurring nucleus is 238U of × intermediates and so favor the SN1 92 protons and 146 protons (mass 4 mechanism. 10–25 kg, radius 9.54 × 10–15 m). Only cer- In practice, however, both routes or some tain combinations of protons and neutrons intermediate mechanism is thought to op- form stable nuclei. Others undergo sponta- erate in many cases. neous decay. See also substitution reaction. A nucleus is depicted by a symbol indicating nucleon number (mass number), nucleoside /new-klee-ŏ-sÿd/ A molecule proton number (atomic number), and ele- 23 consisting of a purine or pyrimidine base ment name. For example, 11Na represents a linked to a sugar, either ribose or deoxyri- nucleus of sodium having 11 protons and bose. ADENOSINE, CYTIDINE, GUANOSINE, mass 23, hence there are (23 – 11) = 12 THYMIDINE, and URIDINE are common nu- neutrons. cleosides. nuclide /new-klÿd/ A nuclear species that nucleotide /new-klee-ŏ-tÿd/ The com- is characterized by a given number of pro- pound formed by condensation of a ni- tons and neutrons; for example, 23Na, trogenous base (a purine, pyrimidine, or 24Na, and 24Mg are all different nuclides. pyridine) with a sugar (ribose or deoxyri- Thus: 23 bose) and phosphoric acid. The nucleic 11Na has 11 protons and 12 neutrons 24 acids are polynucleotides (consisting of 11Na has 11 protons and 13 neutrons 24 chains of many linked nucleotides). 12Mg has 12 protons and 12 neutrons The term is applied to the nucleus and nucleus /new-klee-ŭs/ (pl. nuclei or nucle- often also to the atom.

192 nylon

H H O O N (CH2)6 N CC(CH2)4 H H HO OH

1,6-diaminohexane hexanedioic acid

HN (CH2)6 NH C (CH2)4 C NH (CH2)6

O O

Formation of nylon nylon A type of synthetic polymer linked a molecule containing two amine groups by amide groups –NH.CO–. Nylon poly- with one containing two carboxylic acid mers can be made by copolymerization of groups.

193 O

occlusion /ŏ-kloo-zhŏn/ 1. The process in i.e. preignition of the fuel in the engine. which small amounts of one substance are This depends on the relative proportions of trapped in the crystals of another; for ex- branched-chain and straight-chain hydro- ample, pockets of liquid occluded during carbons present. High proportions of crystallization from a solution. branched-chain alkanes are better in high- 2. Absorption of a gas by a solid; for ex- performance engines. In rating fuels, 2,2,4- ample, the occlusion of hydrogen by palla- trimethylpentane (isooctane) is given a dium. value of 100 and heptane is given a value 0. The performance of a fuel is compared ocher /oh-ker/ A clay mineral containing with a mixture of these hydrocarbons. iron(III) oxide (Fe2O3), used as a yellow, orange, or brown pigment. octavalent /ok-tă-vay-lĕnt/ Having a valence of eight. octadecanoic acid /ok-tă-dek-ă-noh-ik/ (stearic acid; CH3(CH2)16COOH) A solid octaves, law of See Newlands’ law. carboxylic acid present in fats and oils as the glyceride. octet /ok-tet/ A stable shell of eight electrons in an atom. The completion of the octadecenoic acid /ok-tă-dek-ă-noh-ik/ octet gives rise to particular stability and cis-9-octadecenoic acid (or oleic acid) is a this is the basis of the Lewis octet theory naturally occurring carboxylic acid present (named for the American physical chemist (as glycerides) in fats and oils: Gilbert Newton Lewis (1875–1946)), thus: CH3(CH2)7CH:CH(CH2)7COOH 1. The rare gases have complete octets and are chemically inert octahedral complex /ok-tă-hee-drăl/ See 2. The bonding in small covalent molecules complex. is frequently achieved by the central atom completing its octet by sharing octahydrate /ok-tă-hÿ-drayt/ A crys- electrons with other atoms, e.g. CH4. talline compound containing eight mol- 3. The ions formed by electropositive and ecules of water of crystallization per electronegative elements are generally molecule of compound. those with a complete octet, e.g. Na+, Ca2+, O2–, Cl–. octane /ok-tayn/ (C8H18) A liquid alkane obtained from the light fraction of crude oersted Symbol: Oe A unit of magnetic oil. Octane and its isomers are the principal field strength in the c.g.s. system. It is equal constituents of gasoline, which is obtained to 103/4π A m–1. The unit is named for the as the refined light fraction from crude oil. Danish physicist Hans Christian Oersted See also octane rating. (1777–1851). octane rating (octane number) A rating ohm /ohm/ Symbol: Ω The SI unit of elec- for the performance of gasoline in internal- trical resistance, equal to a resistance that combustion engines. The octane rating passes a current of one ampere when there measures the freedom from ‘knocking’ – is an electric potential difference of one

194 optical activity volt across it. 1 Ω = 1 V A–1. Formerly, it onium ion /oh-nee-ŭm/ An ion formed by was defined in terms of the resistance of a addition of a proton (H+) to a molecule. + column of mercury under specified condi- The hydronium ion (H3O ) and ammo- + tions. The unit is named for the German nium ion (NH4 ) are examples. physicist Georg Simon Ohm (1787–1854). oolite /oh-ŏ-lÿt/ A sedimentary rock, a oil Any of various viscous liquids. See type of limestone, that contains small glyceride; petroleum. spherical masses of calcium carbonate (CaCO3). oil of vitriol /vit-ree-ŏl/ Sulfuric(VI) acid. opal /oh-păl/ A naturally occurring hy- oil of wintergreen See methyl salicylate. drated and noncrystalline form of silica (SiO2), valued as a gemstone. Various layers within a gemstone opal can reflect and oil shale A sedimentary rock that includes refract light to give a play of spectral col- in its structure 30–60% of organic matter, ors. There are also milky white and black mainly in the form of bitumen. Heated in varieties. the absence of air it produces an oily substance resembling petroleum, which is rich open-hearth process A method of mak- in nitrogen and sulfur compounds. ing steel by heating pig iron in an open- hearth furnace by burning a mixture of gas oleate /oh-lee-ayt/ A salt or ester of oleic and air. Oxygen is injected through pipes acid; i.e. an octadecenoate. to oxidize impurities and burn off carbon, and lime is used to form a slag. olefin /oh-lĕ-fin/ See alkene. optical activity /op-tă-kăl/ The ability of oleic acid /oh-lee-ik/ See octadecenoic certain compounds to rotate the plane of acid. polarization of plane-polarized light when the light is passed through them. Optical oleum /oh-lee-ŭm/ (pyrosulfuric acid; activity can be observed in crystals, gases, H2S2O7) A colorless fuming liquid formed liquids, and solutions. The amount of rota- by dissolving sulfur(VI) oxide in concen- tion depends on the concentration of the trated sulfuric acid. It gives sulfuric acid on active compound. diluting with water. See contact process. Optical activity is caused by the interaction of the varying electric field of the light oligomer /ŏ-lig-ŏ-mer/ A POLYMER formed with the electrons in the molecule. It occurs from a relatively few monomer molecules. when the molecules are asymmetric – i.e. they have no plane of symmetry. Such mol- oligosaccharide /ol-ă-goh-sakă-rÿd, -rid/ ecules have a mirror image that cannot be superimposed on the original molecule. In A carbohydrate formed of a small number organic compounds this usually means that of monosaccharide units (up to around they contain a carbon atom attached to 20). four different groups, forming a chiral center. The two mirror-image forms of an olivine /ol-ă-veen, ol-ă-veen/ A greenish asymmetric molecule are optical isomers. rock-forming silicate mineral containing One isomer will rotate the polarized light iron and magnesium. Its clear green form is in one sense and the other by the same the gemstone peridot. amount in the opposite sense. Such isomers are described as dextrorotatory or levoro- one-pot synthesis A synthesis of a chem- tatory, according to whether they rotate ical compound in which the reactants form the plane to the ‘right’ or ‘left’ respectively the required product in a single reaction (rotation to the left is clockwise to an ob- mixture. server viewing the light coming toward the

195 optical isomerism

COOH COOH

C C CH3 OH CH3 H

H OH

(R)-lactic acid (S)-lactic acid

Optical isomers of lactic acid

COOH COOH COOH H OH HO H H OH

C C C

H OH HO H H OH COOH COOH COOH

Isomers of tartaric acid

Optical isomers observer). Dextrorotatory compounds are isomer according to specific rules (i.e. the given the symbol d or (+) and levorotatory absolute configuration of the molecule). compounds l or (–). A mixture of the two Sugars are related to a particular configu- isomers in equal amounts does not show ration of glyceraldehyde (2,3-dihydrox- optical activity. Such a mixture is some- ypropanal). For alpha amino acids the corn times called the (±) or dl-form, a racemate, rule is used: the structure of the acid or a racemic mixture RC(NH2)(COOH) H is drawn with H at Optical isomers have identical physical the top; viewed from the top the groups properties (apart from optical activity) and spell CORN in a clockwise direction for all cannot be separated by fractional crystal- D-amino acids (i.e. the clockwise order is lization or distillation. Their general chem- –COOH,R,NH2). The opposite is true for ical behavior is also the same, although L-amino acids. Note that this convention they do differ in reactions involving other does not refer to optical activity: L-alanine optical isomers. Many naturally occurring is dextrorotatory by D-cystine is levorota- substances are optically active (only one tory. optical isomer exists naturally) and bio- An alternative is the R–S convention for chemical reactions occur only with the nat- showing configuration. There is an order ural isomer. For instance, the natural form of priority of attached groups based on the of glucose is d-glucose and living organ- proton number of the attached atom: isms cannot metabolize the l-form. I, Br, Cl, SO3H, OCOCH3, OCH3, OH, The terms ‘dextrorotatory’ and ‘levoro- NO2, NH2, COOCH3, CONH2, COCH3, tatory’ refer to the effect on polarized light. CHO, CH2OH, C6H5, C2H5, CH3, H A more common method of distinguishing Hydrogen has the lowest priority. The two optical isomers is by their D-form or chiral carbon is viewed such that the group L-form. This convention (the D–L conven- of lowest priority is hidden behind it. If the tion) refers to the absolute structure of the other three groups are in descending prior-

196 orbital

C H2N R

COOH

The corn rule for absolute configuration of alpha amino acids

1 1

C C

32 23

R–configuration S–configuration

The R/S system

Absolute configuration

ity in a clockwise direction, the compound tion of plane-polarized light by an optically is R-. If descending priority is anticlockwise active substance depends on the wave- it is S-. length of the light. Plots of rotation against The existence of a carbon atom bound wavelength can be used to give informa- to four different groups is not the strict tion about the molecular structure of opti- condition for optical activity. The essential cally active compounds. point is that the molecule should be asymmetric. Inorganic octahedral complexes, optical rotation Rotation of the plane of for example, can show optical isomerism. polarization of plane-polarized light by an It is also possible for a molecule to contain optically active substance. asymmetric carbon atoms and still have a plane of symmetry. One structure of orbit The path of an electron as it moves tartaric acid has two parts of the mol- around the nucleus in an atom. ecule that are mirror images, thus having a plane of symmetry. This (called the meso- orbital A region around an atomic nu- form) is not optically active. See also reso- cleus in which there is a high probability of lution). finding an electron. The modern picture of the atom according to quantum mechanics optical isomerism See isomerism; optical does not have electrons moving in fixed el- activity. liptical orbits. Instead, there is a finite probability that the electron will be found optical rotary dispersion (ORD) The in any small region at all possible distances phenomenon in which the amount of rota- from the nucleus. In the hydrogen atom the

197 orbital probability is low near the nucleus, in- bitals have more complex shapes, typically creases to a maximum, and falls off to in- with four lobes. finity. It is useful to think of a region in Molecular orbitals are formed by over- space around the nucleus – in the case of lap of atomic orbitals, and again there are hydrogen the region within a sphere – different types. If the orbital is completely within which there is a high chance of find- symmetrical about an axis between the nu- ing the electron. Each of these, called an clei, it is a sigma orbital. This can occur, atomic orbital, corresponds to a sub-shell for instance, by overlap of two s orbitals, and can ‘contain’ a single electron or two as in the hydrogen atom, or two p orbitals electrons with opposite spins. Another way with their lobes along the axis. However, of visualizing an orbital is as a cloud of two p orbitals overlapping at right angles electron charge (the average distribution to the axis form a different type of molecu- with time). lar orbital – a pi orbital – with regions Similarly, in molecules the electrons above and below the axis. Pi orbitals are move in the combined field of the nuclei also formed by overlap of d orbitals. Each and can be assigned to molecular orbitals. molecular orbital can contain a pair of In considering bonding between atoms it is electrons, forming a sigma bond or pi useful to treat molecular orbitals as formed bond. A double bond, for example the by overlap of atomic orbitals. bond in ethene, is a combination of a sigma It is possible to calculate the shapes and bond and a pi bond. energies of atomic and molecular orbitals Hybrid orbitals are atomic orbitals by quantum theory. The shapes of atomic formed by combinations of s, p, and d orbitals depend on the orbital angular mo- atomic orbitals, and are useful in describ- mentum (the sub-shell). For each shell ing the bonding in compounds. There are there is one s orbital, three p orbitals, five various types. In carbon, for instance, the d orbitals, etc. The s orbitals are spherical, electron configuration is 1s22s22p2. Car- the p orbitals each have two lobes; d or- bon, in its outer (valence) shell, has one

z z z

y y y

x x x

dxy orbital dz2 orbital s orbital z z z

y y y

x x x

px orbital py orbital pz orbital

Orbital: atomic orbitals

198 ATOMIC ORBITALS HYBRID ORBITALS SHAPE sp +

one s one p two sp3 linear

sp2 +

one s two p three sp2 planar

sp3 +

one s three p four sp3 tetrahedral

Orbital: hybrid orbitals

s orbitals sigma

px orbitals sigma

C z z

pz orbitals pi

Orbital: molecular orbitals

199 ORD filled s orbital, two filled p orbitals, and ore dressing See beneficiation. one ‘empty’ p orbital. These four orbitals may hybridize (sp3 hybridization) to act as organic acid /or-gan-ik/ An organic com- four equal orbitals arranged tetrahedrally, pound that can release hydrogen ions (H+) each with one electron. In methane, each to a base, such as a CARBOXYLIC ACID or a hybrid orbital overlaps with a hydrogen s PHENOL. See acid. orbital to form a sigma bond. Alterna- tively, the s and two of the p orbitals may organic base An organic compound that hybridize (sp2 hybridization) and act as can function as a base. Organic bases are three orbitals in a plane at 120°. The re- typically amines that gain H+ ions. See maining p orbital is at right angles to the amine; base. plane, and can form pi bonds. Finally, sp hybridization may occur, giving two or- organic chemistry The chemistry of bitals in a line. More complex types of hy- compounds of carbon. Originally the term bridization, involving d orbitals, explain organic chemical referred to chemical com- the geometries of inorganic complexes. pounds present in living matter, but now it The combination of two atomic orbitals covers any carbon compound with the ex- in fact produces two molecular orbitals. ception of certain simple ones, such as the One – the bonding orbital – has a concen- carbon oxides, carbonates, cyanides, and tration of electron density between the nu- cyanates. These are generally studied in in- clei, and thus tends to hold the atoms organic chemistry. The vast numbers of together. The other – the antibonding or- synthetic and natural organic compounds bital – has slightly higher energy and tends exist because of the ability of carbon to to repel the atoms. If both atomic orbitals form chains of atoms (catenation). Other are filled, the two molecular orbitals are elements are involved in organic com- also filled and cancel each other out – there pounds; principally hydrogen and oxygen is no net bonding effect. If each atomic or- but also nitrogen, halogens, sulfur, and bital has one electron, the pair occupies the phosphorus. lower energy bonding orbital, producing a net attraction. organometallic compound /or-gă-noh- mĕ-tal-ik/ An organic compound contain- ORD See optical rotary dispersion. ing a carbon–metal bond. Tetraethyl lead, (C2H5)4Pb, is a typical example of an order The sum of the indices of the con- organometallic compound, used as an ad- centration terms in the expression that de- ditive in petrol. termines the rate of a chemical reaction. For example, in the expression ortho- 1. Designating the form of a di- rate = k[A]x[B]y atomic molecule in which both nuclei have x is called the order with respect to A, y the the same spin direction; e.g. orthohydro- order with respect to B, and (x + y) the gen, orthodeuterium. order overall. The values of x and y are not 2. Designating a benzene compound with necessarily equal to the coefficients of A substituents in the 1,2 positions. The posi- and B in the molecular equation. Order is tion next to a substituent is the ortho posi- an experimentally determined quantity de- tion on the benzene ring. This was used in rived without reference to any equation or the systematic naming of benzene deriva- mechanism. Fractional orders do occur. tives. For example, orthodinitrobenzene For example, in the reaction (or o-dinitrobenzene) is 1,2-dinitroben- → CH3CHO CH4 + CO zene. 1.5 the rate is proportional to [CH3CHO] 3. Certain acids, regarded as formed from i.e. it is of order 1.5. an anhydride and water, were named ortho acids to distinguish them from the less hy- ore A mineral source of a chemical ele- drated meta acids. For example, H4SiO4 ment. (from SiO2 + 2H2O) is orthosilicic acid; 200 osmotic pressure

H2SiO3 (SiO2 + H2O) is metasilicic acid. portance in transport and control mecha- See also meta-; para-. nisms in biological systems; for example, plant growth and general cell function. orthoboric acid /or-thŏ-bô-rik/ See boric Osmosis is a colligative property and its acid. theoretical treatment is similar to that for the lowering of vapor pressure. The mem- orthohydrogen /or-thoh-hÿ-drŏ-jĕn/ See brane can be regarded as equivalent to the hydrogen. liquid-vapour interface, i.e. one that permits free movement of solvent molecules orthophosphoric acid /or-thoh-fos-fô- but restricts the movement of solute mol- rik/ See phosphoric(V) acid. ecules. The solute molecules occupy a certain area at the interface and therefore orthophosphorous acid /or-thoh-fos-fŏ- inhibit solvent egress from the solution. rŭs/ See phosphonic acid. Just as the development of a vapor pressure in a closed system is necessary for orthorhombic crystal /or-thŏ-rom-bik/ liquid–vapour equilibrium, the develop- See crystal system. ment of an OSMOTIC PRESSURE on the solution side is necessary for equilibrium at the osmiridium /oz-mă-rid-ee-ŭm/ A natu- membrane. rally occurring alloy of osmium and iridium, used to make the tips of pen nibs. See osmotic pressure Symbol: π The pressure iridium; osmium. that must be exerted on a solution to prevent the passage of solvent molecules into /oz-mee-ŭm/ A transition metal osmium it when the solvent and solution are sepa- that is found associated with platinum. Os- rated by a semipermeable membrane. The mium is the most dense of all metals. It has osmotic pressure is therefore the pressure a characteristic smell resulting from the required to maintain equilibrium between production of osmium(VIII) oxide (os- the passage of solvent molecules through mium tetroxide, OsO ). The metal is used 4 the membrane in either direction and thus in catalysts and in alloys for pen nibs, piv- prevent the process of osmosis proceeding. ots, and electrical contacts. Symbol: Os; m.p. 3054°C; b.p. 5027°C; The osmotic pressure can be measured by r.d. 22.59 (20°C); p.n. 76; r.a.m. 190.23. placing the solution, contained in a small perforated thimble covered by a semiper- osmium(IV) oxide (osmium tetroxide; meable membrane and fitted with a length of glass tubing, in a beaker of the pure sol- OsO4) A volatile yellow crystalline solid with a penetrating odor, used as an oxidiz- vent. Solvent molecules pass through the ing agent and, in aqueous solution, as a membrane, diluting the solution and catalyst for organic reactions. thereby increasing the volume on the solution side and forcing the solution to rise up osmium tetroxide /te-troks-ÿd/ See os- the glass tubing. The process continues mium(IV) oxide. until the pressure exerted by the solvent molecules on the membrane is balanced by osmosis /oz-moh-sis/ Systems in which a the hydrostatic pressure of the solution in solvent is separated from a solution by a the tubing. A sample of the solution is then semipermeable membrane approach equi- removed and its concentration determined. librium by solvent molecules on the solvent Osmosis is a colligative property; therefore side of the membrane migrating through it the method can be applied to the determi- to the solution side; this process is called nation of relative molecular masses, partic- osmosis and always leads to dilution of the ularly for large molecules, such as proteins, solution. The phenomenon is quantified by but it is restricted by the difficulty of measurement of the osmotic pressure. The preparing good semipermeable mem- process of osmosis is of fundamental im- branes.

201 Ostwald’s dilution law

As the osmotic pressure is a colligative oxidation–reduction See redox. property it is directly proportional to the molar concentration of the solute if the oxide /oks-ÿd/ A compound of oxygen temperature remains constant; thus π is and another element. Oxides can be made proportional to the concentration n/V, by direct combination of the elements or by where n is the number of moles of solute, heating a hydroxide, carbonate, or other and V the solvent volume. The osmotic salt. See also acidic oxide; basic oxide; neu- pressure is also proportional to the ab- tral oxide; peroxide. solute temperature. Combining these two proportionalities gives πV = nCT, which oxidizing acid /oks-ă-dÿ-zing/ An acid has the same form as the gas equation, PV that acts as an oxidizing agent, e.g. sulfu- = nRT, and experimental values of C are ric(VI) acid or nitric(V) acid. Because it is similar to those for R, the universal gas oxidizing, nitric(V) acid can dissolve met- constant. This gives considerable support als below hydrogen in the electromotive se- to the kinetic theory of colligative proper- ries: → ties. 2HNO3 + M MO + 2NO2 + H2O → MO + 2HNO3 H2O + M(NO3)2 Ostwald’s dilution law /ost-valts/ See dissociation constant. oxidizing agent See oxidation. oxalate /oks-ă-layt/ A salt or ester of oxime /oks-eem, -im/ A type of organic ethanedioic acid (oxalic acid). See ethane- compound containing the C:NOH group, formed by reaction of an aldehyde or ke- dioic acid. tone with hydroxylamine (NH2OH). oxalic acid /oks-al-ik/ See ethanedioic oxo process A method of manufacturing acid. aldehydes by passing a mixture of carbon monoxide, hydrogen, and alkanes over a oxidant /oks-ă-dănt/ An oxidizing agent. cobalt catalyst at high pressure (100 at- In rocket fuels, the oxidant is the substance mospheres and 150°C). The aldehydes can that provides the oxygen for combustion subsequently be reduced to alcohols, mak- (e.g. liquid oxygen or hydrogen peroxide). ing the process a useful source of alcohols of high molecular weight. oxidation /oks-ă-day-shŏn/ An atom, an ion, or a molecule is said to undergo oxi- 2-oxopropanoic acid /oks-oh-proh-pă- dation or to be oxidized when it loses elec- noh-ik/ (pyruvic acid; CH3COCOOH) A trons. The process may be effected colorless liquid carboxylic acid containing chemically, i.e. by reaction with an oxidiz- a keto (–CO) group. It is important in ing agent, or electrically, in which case ox- metabolic reactions in the body. idation occurs at the anode. For example, → + – 2Na + Cl2 2Na + 2Cl oxyacid /oks-ee-ass-id/ An ACID in which where chlorine is the oxidizing agent and the replaceable hydrogen atom is part of a sodium is oxidized, and hydroxyl group, including carboxylic – 2+ → 4CN + 2Cu C2N2 + 2CuCN acids, phenols and inorganic acids such as where Cu2+ is the oxidizing agent and CN– phosphoric(V) acid and sulfuric(VI) acid. is oxidized. The oxidation state of an atom is indi- oxygen /oks-ă-jĕn/ A colorless odorless di- cated by the number of electrons lost or ef- atomic gas; the first member of group 16 of fectively lost by the neutral atom, i.e. the the periodic table. It has the electronic con- oxidation number. The oxidation number figuration [He]2s22p4 and its chemistry in- of a negative ion is negative. The process of volves the acquisition of electrons to form oxidation is the converse of reduction. See either the di-negative ion, O2– or two cova- also redox. lent bonds. In each case the oxygen atom

202 oxygen attains the configuration of the rare gas tive elements among the non-metals gener- neon. ally form weaker acids, e.g. B(OH)3 and Oxygen is the most plentiful element in H2CO3. The more electronegative elements the Earth’s crust accounting for over 40% form stronger acids. The higher the oxida- by weight. It is present in the atmosphere tion state of the central atom the stronger < < (20%) and is a constituent of the majority the acid (HOCl HClO2 HClO4). Non- of minerals and rocks (e.g. sandstones, metal oxides may be gaseous (SO2, CO2), SiO2, carbonates, CaCO3, aluminosili- liquid (N2O4), or solid (P2O5). The weakly cates) as well as the major constituent of non-metallic elements such as silicon may the sea. Oxygen is an essential element for require bases for dissolution and in some almost all living things. Elemental oxygen cases the oxides have extended polymeric has two forms: the diatomic molecule O2 structures, e.g., SiO2. In between the acidic and the less stable molecule trioxygen and basic oxides are the amphoteric ox- (ozone), O3, which is formed by passing an ides, which behave acidically to strong electric discharge through oxygen gas. bases and basically towards strong acids. There are several convenient laboratory This behavior is associated with elements routes to oxygen: that are physically metallic but are chemi- 1. Heat on unstable oxides. cally only weakly cationic, e.g., ZnO gives → 2– 2HgO 2Hg + O2 Zn with acids and the zincates, 2– 2. Decomposition of peroxides. Zn(OH)4 , with bases. There is also a → 2H2O2 2H2O + O2 small class of mixed oxides that can be re- 3. Heat on ‘-ate’ compounds such as chlo- garded as salts between a ‘basic’ and an rates or manganate(VII). ‘acidic’ oxide of the same metal: for exam- → 2KClO3 KCl + 3O2 ple, → → 2KMnO4 K2MnO4 + MnO2 + O2 FeO + Fe2O3 Fe(FeO2)2 = Fe3O4 → Industrially oxygen is obtained by the 2PbO + PbO2 Pb3O4 fractionation of liquid air. The neutral oxides are essentially insol- Oxygen reacts with elements from all uble non-metal oxides such as N2O, NO, groups of the periodic table except group 0 CO, F2O, although extreme conditions can and even this unreactive group forms sev- lead to some degree of acidic behavior in eral compounds containing oxygen (XeO3, the case of CO, for example, 2– – → – XeO4, XeOF2, XeO2 ). CO + OH HCOO The nature of the oxides has long been Oxygen occurs in three natural isotopic a convenient guide to metallic and non- forms, 16O (99.76%), 17O (0.0374%), 18O metallic character. Thus, metals typically (0.2039%); the rarer isotopes are used in combine with oxygen to form oxides, detailed studies of the behavior of oxygen- which if soluble react with water to form containing groups during reactions (tracer bases (via OH– ion); the more electroposi- studies). tive the metal the more vigorous the reac- Oxygen is very limited in its catenation tion. Most of the group 1 and group 2 but an interesting range of O–O species is 2– metals behave like this forming oxides, formed by the following: O2 peroxide, 2– 2– – + O , (e.g., Na2O, CaO), peroxides, O2 , O2 superoxide, O2 oxygen gas, O2 – (e.g., Na2O2, BaO2), and superoxides, O2 , oxygenyl cation. The O–O bond gets both (e.g., RbO2, CsO2). Oxides of metallic ele- progressively shorter and stronger in the ments are solids and x-ray studies show series. The peroxides are formed with Na, that discrete O2– ions do exist in the solid Ca, Sr, and Ba and are formally related to state even though they do not exist in solu- hydrogen peroxide (prepared by the action tion: of acids on ionic peroxides). The superox- 2– → – O + H2O 2OH ides of K, Rb, and Cs are prepared by burn- The non-metals typically form molecu- ing the metal in air (the less electropositive lar oxides such as SO2, ClO2, and NO2. metals, Na, Mg, and Zn form less stable + When soluble in water they generally dis- superoxides). Oxygenyl cation, O2 , is solve to form acids. The less electronega- formed by reaction of PtF6 (which has a 203 ozone high electron affinity) with oxygen at room Ozone is a strong oxidizing agent. Its temperature. Other oxygenyl cation concentration can be determined by react- species can be made with group 15 fluo- ing it with iodide ions and titrating the io- + – rides, e.g. O2 AsF6 . dine formed with standard sodium ° Symbol: O; m.p. –218.4 C; b.p. thiosulfate(VI). It forms ozonides with ° –3 ° –182.962 C; d. 1.429 kg m (0 C); p.n. 8; alkenes. See ozonolysis. r.a.m. 15.9994. ozonide /oh-zŏ-nÿd/ See ozonolysis. ozone /oh-zohn/ (trioxygen; O3) A poisonous, blue-colored allotrope of oxygen ozonolysis /oh-zŏ-nol-ă-sis/ The addition made by passing oxygen through a silent of ozone (O ) to alkenes and the subse- electric discharge. Ozone is unstable and 3 quent hydrolysis of the ozonide into hy- decomposes to oxygen on warming. It is present in the upper layers of the atmos- drogen peroxide and a mixture of carbonyl phere, where it screens the Earth from compounds. The carbonyl compounds can harmful short-wave ultraviolet radiation. be separated and identified, which in turn, There is concern that the ozone layer is identifies the groups and locates the posi- possibly being depleted by the use of fluo- tion of the double bond in the original rocarbons and other compounds produced alkene. Ozonolysis was formerly an impor- by industry. tant analytical technique.

R’ R R’ R O3 C C C C

O O O alkene primary ozonide

R O R’ R R’ H+ C C C O CO H O 2 OO H2O2 secondary ozonide Ozonolysis of an alkene to form a mixture of carbonyl compounds

204 P

PAH See particulate matter. widely used for the analysis of mixtures. Paper chromatography usually employs a paint A suspension of powdered pigment specially produced paper as the stationary in a liquid vehicle, used for decorative and phase. A base line is marked in pencil near protective surface coatings. In oil-based the bottom of the paper and a small sample paints, the vehicle contains solvents and a of the mixture is spotted onto it using a drying oil or synthetic resin. In water- capillary tube. The paper is then placed based or emulsion paints, the vehicle is vertically in a suitable solvent, which rises mostly water with an emulsified resin. up to the base line and beyond by capillary action. The components within the sample palladium /pă-lay-dee-ŭm/ A silvery mixture dissolve in this mobile phase and white ductile transition metal occurring in are carried up the paper. However, the platinum ores in Canada and as the native paper holds a quantity of moisture and metal in Brazil. Most palladium is obtained some components will have a greater ten- as a by-product in the extraction of copper dency than others to dissolve in this mois- and zinc. It is used in electrical relays and ture than in the mobile phase. In addition, as a catalyst in hydrogenation processes. some components will cling to the surface Hydrogen will diffuse through a hot palla- of the paper. Therefore, as the solvent dium barrier. moves through the paper, certain compo- Symbol: Pd; m.p. 1552°C; b.p. 3140°C; nents will be left behind and separated r.d. 12.02 (20°C); p.n. 46; r.a.m. 106.42. from each other. When the solvent has almost reached palmitic acid /pal-mit-ik/ See hexade- the top of the paper, the paper is removed canoic acid. and quickly dried. The paper is developed to locate the positions of colorless fractions paper chromatography A technique by spraying with a suitable chemical, e.g. ninhydrin, or by exposure to ultraviolet radiation. The components are identified by comparing the distance they have traveled up the paper with standard solutions that have been run simultaneously, or by computing an RF value. A simplified version of developing paper chromatography uses a piece of filter chamber paper. The sample is spotted at the center of the paper and solvent passed through it. Separation of the components of the mix- paper strip ture again takes place as the mobile phase spreads out on the paper. mobile phase Paper chromatography is an application of the partition law. spotted samples para- 1. Designating the form of a di- Apparatus for paper chromatography atomic molecule in which both nuclei have

205 paraffin opposite spin directions; e.g. parahydro- gas would have if it alone were present in gen, paradeuterium. the same volume. See Dalton’s law. 2. Designating a benzene compound with substituents in the 1,4 positions. The posi- particulate matter (PM) An airborne tion on a benzene ring directly opposite a pollutant consisting of small particles of substituent is the para position. This was silicate, carbon, or large polyaromatic hy- used in the systematic naming of benzene drocarbons (PAHs). These pollutants are compounds. For example, para-dinitro- often referred to as particulates. They are benzene (or p-dinitrobenzene) is 1,4-dini- classified according to size; e.g. PM10 is trobenzene. particulate matter formed of particles less See also meta-; ortho-. than 10 µm diameter. paraffin /pa-ră-fin/ 1. See petroleum. particulates See particulate matter. 2. See alkane. partition coefficient If a solute dissolves paraffin oil See kerosene. See also petro- in two non-miscible liquids, the partition leum. coefficient is the ratio of the concentration in one liquid to the concentration in the paraffin wax A solid mixture of hydro- other liquid. carbons, obtained from petroleum. pascal /pas-kăl/ Symbol: Pa The SI unit of paraformaldehyde /pa-ră-for-mal-dĕ-hÿd/ pressure, equal to a pressure of one newton See methanal. per square meter (1 Pa = 1 N m–2). The unit is named for the French mathematician, parahydrogen /pa-ră-hÿ-drŏ-jĕn/ See hy- physicist, and religious philosopher Blaise drogen. Pascal (1623–62). paraiodic (VII) acid /pa-ră-ÿ-od-ik/ See Paschen series /pash-ĕn/ A series of lines iodic (VII) acid. in the infrared spectrum emitted by excited hydrogen atoms. The lines correspond to paraldehyde /pă-ral-dĕ-hÿd/ See ethanal. the atomic electrons falling into the third lowest energy level and emitting energy as paramagnetism /pa-ră-mag-nĕ-tiz-ăm/ radiation. The wavelength (λ) of the radia- See magnetism. tion in the Paschen series is given by 1/λ = R(1/32 – 1/n2) where n is an integer and R partial ionic character The electrons of is the Rydberg constant. The series is a covalent bond between atoms or groups named for the German physicist Louis with different electronegativities will be Paschen (1865–1947). See also spectral se- polarized towards the more electronegative ries. constituent; the magnitude of this effect can be measured by the ionic character of passive Describing a metal that is unreac- the bond. When the effect is small the bond tive because of the formation of a thin pro- is referred to simply as a polar bond and is tective layer. Iron, for example, does not adequately treated using dipole moments; dissolve in concentrated nitric(V) acid be- as the effect grows the theoretical treat- cause of the formation of a thin oxide ment requires other contributions to ionic layer. character. Examples of partial ionic character (from nuclear quadrupole resonance) Pauli exclusion principle /pow-lee/ See are H–I, 21%; H–Cl, 40%; Li–Br, 90%;. exclusion principle. partial pressure In a mixture of gases, the p-block elements The elements of the contribution that one component makes to main groups 13 (B to Tl), 14 (C to Pb), 15 the total pressure. It is the pressure that the (N to Bi), 16 (O to Po), 17 (F to At), and 18

206 pericyclic reaction

(He to Rn). They are so called because they mass) of each of the elements that make it have outer electronic configurations that up. It is calculated by dividing the mass of have occupied p levels. each element (taking into account the number of atoms present) by the relative mole- PCB See polychlorinated biphenyl. cular mass of the whole molecule. For example, methane (CH4) has a relative pearl A lustrous accretion of calcium car- molecular mass of 16 and its percentage bonate (nacre, CaCO3) that builds up on a composition is 12/16 = 75% carbon and (4 particle of foreign matter inside the shells × 1)/16 = 25% hydrogen. of oysters and some other mollusks. perchloric acid /per-klor-ik, -kloh-rik/ pearl spar See dolomite. See chloric(VII) acid. peat A brown or black material formed by perfect gas (ideal gas) See gas laws; ki- the partial decomposition of plant remains netic theory. in marshy ground, the first stage in the formation of coal. It is used for making char- pericyclic reaction /pe-ră-sÿ-klik/ A type coal and compost, and, when dried, can be of CONCERTED REACTION in which the tran- burned as a fuel. sition state is cyclic and can be regarded as formed by movement of electrons in a cir- PEC See photoelectrochemical cell. cle, from one bond to an adjacent bond. It is usual to distinguish three types of peri- pentahydrate /pen-tă-hÿ-drayt/ A crys- cyclic reaction: talline compound that has five molecules Cycloadditions. In these reactions a conju- of water of crystallization per molecule of gated diene adds to a double bond to form compound. a ring. This involves the formation of two new sigma bonds. The DIELS–ALDER REAC- pentane /pen-tayn/ (C5H12) A straight- TION is a cycloaddition. The reverse reac- chain alkane obtained by distillation of tion, in which a ring containing a double crude oil. bond breaks to a diene and a compound containing a double bond, is also a peri- pentanoic acid /pen-tă-noh-ik/ (valeric cyclic reaction. acid; CH3(CH2)3COOH) A colorless li- Sigmatropic rearrangements. In these reac- quid carboxylic acid, used in making per- tions a sigma bond breaks and another is fumes. formed. The COPE REARRANGEMENT is an example. pentavalent /pen-tă-vay-lĕnt, pen-tav-ă-/ Electrocyclic reactions. In these reactions a (quinquevalent) Having a valence of five. ring is formed across the ends of a conjugated system of double bonds. The reverse pentose /pen-tohs/ A SUGAR that has five reaction, in which a ring containing two carbon atoms in its molecules. double bonds breaks by movement of elec- pentyl group /pen-tăl/ (amyl group) The group CH3CH2CH2CH2CH2–. R H O R peptide /pep-tÿd/ A compound formed by linkage of two or more amino-acid groups C N C C together. percentage composition A way of ex- H H pressing the composition of a chemical compound in terms of the percentage (by Peptide linkage

207 peridot trons in a cycle, is also an electrocyclic re- columns of related elements are called action. GROUPS. Down a group there is an increase Pericyclic reactions are often treated using in atomic size and in electropositive (metal- FRONTIER-ORBITAL theory or the WOOD- lic) behavior. WARD–HOFFMANN RULES. Originally the periodic table was arranged in eight groups with the alkali peridot /pe-ră-dot/ See olivine. metals as group I, the halogens as group VII, and the rare gases as group 0. The period One of the horizontal rows in the transition elements were placed in a block conventional periodic table. Each period in the middle of the table. Groups were represents the elements arising from pro- split into two sub-groups. For example, gressive filling of the outer shell (i.e. the ad- group I contained the main-group ele- dition of one extra electron for each new ments, Li, Na, K, Rb, Cs, in subgroup IA element), the elements being arranged in and the subgroup IB elements, Cu, Ag, Au. order of ascending proton number. In a The system was confusing because there strict sense hydrogen and helium represent was a difference in usage for subgroups one period but convention refers to the el- and the current form of the table has 18 ements lithium to neon (8 elements) as the groups (see Appendix). first short period (n = 2), and the elements sodium to argon (8 elements) as the second permanent gas A gas that cannot be liq- short period (n = 3). With entry to the n = uefied by pressure alone – that is, a gas 4 level there is filling of the 4s, then back above its critical temperature. See critical filling of the 3d, before the 4p are filled. temperature. Thus this set contains a total of 18 electrons (potassium to krypton) and is called permanent hardness A type of water a long period. The next set, rubidium to hardness caused by the presence of dis- xenon, is similarly a long period. See also solved calcium, iron, and magnesium sul- Aufbau principle. fates or chlorides. This form of hardness cannot be removed by boiling. Compare periodic acid See iodic(VII) acid. temporary hardness. See also water softening. periodic law The law upon which the modern periodic table is based. Enunciated permanganate /per-mang-gă-nayt, -nit/ in 1869 by Mendeléev, this law stated that See manganate(VII). the properties of the elements are a periodic function of their atomic weights: if Permutit (Trademark) A substance used arranged in order of increasing atomic to remove unwanted chemicals that have weight then elements having similar prop- dissolved in water. It is a zeolite consisting erties occur at fixed intervals. Certain ex- of a complex chemical compound, sodium ceptions or gaps in the table lead to the aluminum silicate. When hard water is view that the nuclear charge is a more char- passed over this material, calcium and acteristic function, thus the modern state- magnesium ions exchange with sodium ment of the periodic law is that the physical ions in the Permutit. This is a good exam- and chemical properties of elements are a ple of ion exchange. Once all the available periodic function of their proton number. sodium ions have been used up, the Permu- tit can be regenerated by washing it with a periodic table A table of the elements saturated solution of sodium chloride. The arranged in order of increasing proton excess of sodium ions now exchange with number to show similarities in chemical the calcium and magnesium ions in the Per- behavior between elements. Horizontal mutit. rows of elements are called PERIODS. Across a period there is a general trend from peroxide /pĕ-roks-ÿd/ 1. An oxide con- metallic to non-metallic behavior. Vertical taining the –O–O– ion.

208 phase

2. A compound containing the –O–O– Kerosene (paraffin) in the range ° group. 160–250 C, consisting mainly of C11 and C12 hydrocarbons. It is a fuel both for do- peroxosulfuric(VI) acid /pĕ-roks-oh-sul- mestic heating and jet engines. fyoor-ik/ (Caro’s acid; H2SO5) A white Gasoline (petrol) in the range 40–180°C, crystalline solid formed by reacting hydro- consisting mainly of C5–C10 hydrocarbons. gen peroxide with sulfuric acid. It is a pow- It is used as motor fuel and as a raw ma- erful oxidizing agent. The acid is also terial for making other chemicals. named for the German chemist Heinrich Refinery gas, consisting of C1–C4 gaseous Caro (1834–1910). hydrocarbons. In addition lubricating oils and paraffin perturbation theory An approximation wax are obtained from the residue. The technique in which a system is divided into black material left is bitumen tar. two parts, with one part that can be solved exactly and a second part that makes the petroleum ether A flammable mixture of system too complicated to be solved ex- hydrocarbons, mainly pentane and hexane, actly. For perturbation theory to be applic- used as a solvent. Note that it is not an able it is necessary that the second part is a ether. small correction to the first part. The effects of the small corrections are expressed pewter A tarnish-resistant alloy of tin and as an infinite series, called a perturbation lead, usually containing 80–90% tin. Mod- series, which modifies the results that ern pewter is hardened by antimony and could be calculated exactly. A classic ex- copper, which in the best grades replace the ample of perturbation theory is the modifi- lead content. It is lighter than old pewter cation of the orbits of planets round the and having a bright or a soft satiny finish is Sun because of their gravitational interac- often used for decorative and ceremonial tions with other planets. In quantum me- purposes. chanics an application of perturbation theory is the calculation of the effects of pH The logarithm to base 10 of the recip- small electric or magnetic fields on atomic rocal of the hydrogen-ion concentration of energy levels. a solution. In pure water at 25°C the concentration of hydrogen ions is 1.00 × 10–7 peta- Symbol: P A prefix denoting 1015. mol l–1, thus the pH equals 7 at neutrality. petrochemicals /pet-roh-kem-ă-kălz/ An increase in acidity increases the value of + Chemicals that are obtained from crude oil [H ], decreasing the value of the pH below or from natural gas. 7. An increase in the concentration of hydroxide ion [OH–] proportionately de- + petrol See petroleum. creases [H ], therefore increasing the value of the pH above 7 in basic solutions. pH petroleum A mixture of hydrocarbons values can be obtained approximately by formed originally from marine animals and using indicators. More precise measure- plants, found beneath the ground trapped ments use electrode systems. between layers of rock. It is obtained by drilling (also called crude oil). Different phase /fayz/ One of the physically separa- oilfields produce petroleum with differing ble parts of a chemical system. For exam- compositions. The mixture is separated ple, a mixture of ice (solid phase) and into fractions by fractional distillation in a water (liquid phase) consists of two phases. vertical column. The main fractions are: A system consisting of only one phase is Diesel oil (gas oil) in the range 220–350°C, said to be homogeneous. A system consist- consisting mainly of C13–C25 hydrocar- ing of more than one phase is said to be bons. It is used in diesel engines. heterogeneous.

209 phase diagram phase diagram A graphical representa- 1. Replacement of the hydroxyl group with tion of the state in which a substance will a chlorine atom using phosphorus(V) occur at a given pressure and temperature. chloride. The lines show the conditions under which 2. Reaction with acyl halides to form esters more than one phase can coexist at equi- of carboxylic acids. librium. For one-component systems (e.g. 3. Reaction with haloalkanes under alka- water) the point at which all three phases line conditions to give mixed alkyl–aryl can coexist at equilibrium is called the ethers. triple point and is the point on the graph at In addition phenol can undergo further which the pressure–temperature curves in- substitution on the benzene ring. The hy- tersect. droxyl group directs other substituents into the 2- and 4-positions. phase equilibrium A state in which the phenolphthalein /fee-nol-thal-een, -nohl-, proportions of the various phases in a -fthal-/ An acid–base indicator that is col- chemical system are fixed. When two or orless in acid solutions and becomes red if more phases are present at fixed tempera- the pH rises above the transition range of ture and pressure a dynamic condition will 8–9.6. It is used as the indicator in titra- be established in which individual particles tions for which the end point lies clearly on will leave one phase and enter another; at the basic side (pH > 7), e.g. oxalic acid or equilibrium this will be balanced by an potassium hydrogentartrate against caustic equal number of particles making the re- soda. verse change, leaving the total composition unchanged. phenoxy resin /fi-noks-ee/ A type of thermoplastic resin made by condensation of phase rule In a system at equilibrium the phenols. number of phases (P), number of components (C), and number of degrees of free- phenylalanine /fen-ăl-al-ă-neen, fee-năl-/ dom (F) are related by the formula: See amino acids. P + F = C + 2 phenylamine /fen-al-am-een, fee-năl-/ See phenol /fee-nol, -nohl/ 1. (carbolic acid, aniline. hydroxybenzene, C6H5OH) A white crystalline solid used to make a variety of other phenylethene /fen-ăl-eth-een, fee-năl-/ organic compounds. (styrene; C6H5CHCH2) A liquid hydrocar- 2. A type of organic compound in which at bon used as the starting material for the least one hydroxyl group is bound directly production of polystyrene. The manufac- to one of the carbon atoms of an aromatic ture of phenylethene is by dehydrogenation of ethyl benzene: ring. Phenols do not show the behavior C H C H → C H CH:CH + H typical of alcohols. In particular they are 6 5 2 5 6 5 2 2 more acidic because of the electron-with- phenyl group /fen-ăl, fee-năl/ The group drawing effect of the aromatic ring. The C H –, derived from benzene. preparation of phenol itself is by fusing the 6 5 sodium salt of the sulfonic acid with phenylhydrazone /fen-ăl-hÿ-dră-zohn, sodium hydroxide: fee-năl-/ See hydrazone. → C6H5SO2.ONa + 2NaOH C6H5ONa + Na2SO3 + H2O phenylmethanol /fen-ăl-meth-ă-nol, fee- The phenol is then liberated by sulfuric năl-, -nohl/ (benzyl alcohol; C6H5CH2OH) acid: An aromatic primary alcohol. Phenyl- → 2C6H5ONa + H2SO4 2C6H5OH + methanol is synthesized by Cannizzaro’s Na2SO4 reaction, which involves the simultaneous Reactions of phenol include: oxidation and reduction of benzenecar-

210 phosphorescence baldehyde (benzaldehyde) by refluxing in hydride; PH3) A colorless gas that is an aqueous solution of sodium hydroxide: slightly soluble in water. It has a character- → 2C6H5CHO C6H5CH2OH + istic fishy smell. It can be made by reacting C6H5COOH water and calcium phosphide or by the ac- Phenylmethanol undergoes the reaction of yellow phosphorus on a concen- tions characteristic of alcohols, especially trated alkali. Phosphine usually ignites those in which the formation of a stable spontaneously in air because of contamina- carbonium ion as an intermediate tion with diphosphine. It decomposes into + ° (C6H5CH2 ) enhances the reaction. Substi- its elements if heated to 450 C in the ab- tution onto the benzene ring is also possi- sence of oxygen and it burns in oxygen or ble; the –CH2OH group directs into the 2- air to yield phosphorus oxides. It reacts or 4-position by the donation of electrons with solutions of metal salts to precipitate to the ring. phosphides. Like its nitrogen analog ammonia it forms salts, called phosphonium phenyl methyl ketone (acetophenone; salts. It also forms complex addition com- C6H5COCH3) A colorless sweet-smelling pounds with metal ions. As in ammonia, organic liquid, which solidifies below one or more of the hydrogen atoms can be 20°C. It is used as a solvent for methyl and replaced by alkyl groups. ethyl cellulose plastics. phosphinic acid /fos-fin-ik/ (hypophos- 3-phenylpropenoic acid /fen-ăl-proh-pĕ- phorous acid; H3PO2) A white crystalline noh-ik, fee-năl-/ (cinnamic acid; solid. It is a monobasic acid forming the – C6H5CH:CHCOOH) A white pleasant- anion H2PO2 in water. The sodium salt, smelling crystalline carboxylic acid. It oc- and hence the acid, can be prepared by curs in amber but can be synthesized and is heating yellow phosphorus with sodium used in perfumes and flavorings. hydroxide solution. The free acid and its salts are powerful reducing agents. Phillips process A method for the manufacture of high-density polyethene using a phosphonic acid /fos-fon-ik/ (phospho- catalyst of chromium(III) oxide on a pro- rous acid; orthophosphorous acid; H3PO3) moter of silica and alumina. The reaction A colorless deliquescent solid that can be conditions are 150°C and 30 atm pressure. prepared by the action of water on phos- See also Ziegler process. phorus(III) oxide or phosphorus(III) chloride. It is a dibasic acid producing the – 2– Philosopher’s stone See alchemy. anions H2PO3 and HPO3 in water. The acid and its salts are slow reducing agents. phlogiston theory /floh-jis-tŏn/ A former On warming, phosphonic acid decomposes theory of combustion (disproved in the to phosphine and phosphoric(V) acid. eighteenth century by Lavoisier). Flamma- ble compounds were supposed to contain a phosphonium ion /fos-foh-nee-ŭm/ The + substance (phlogiston), which was released ion PH4 derived from phosphine. when they burned, leaving ash. phosphonium salt See phosphine. phosgene /fos-jeen/ See carbonyl chloride. phosphor /fos-fer/ A substance that phosphates /fos-fayts/ See phosphoric(V) shows luminescence or phosphorescence. acid. phosphorescence /fos-fŏ-ress-ĕns/ 1. The phosphide /fos-fÿd, -fid/ A compound of absorption of energy by atoms followed by phosphorus with a more electropositive el- emission of electromagnetic radiation. ement. Phosphorescence is a type of luminescence, and is distinguished from fluorescence by phosphine /fos-feen, -fin/ (phosphorus(III) the fact that the emitted radiation contin-

211 phosphoric(V) acid ues for some time after the source of exci- Phosphates are useful in water softening tation has been removed. In phosphores- and as fertilizers. cence the excited atoms have relatively long lifetimes before they make transitions phosphorous acid /fos-fŏ-rŭs, fos-for-ŭs, to lower energy states. However, there is -foh-rŭs/ See phosphonic acid. no defined time distinguishing phosphorescence from fluorescence. phosphorus /fos-fŏ-rŭs/ A reactive solid 2. In general usage the term is applied to non-metallic element; the second element the emission of ‘cold light’ – light produced in group 15 of the periodic table. It has the without a high temperature. The name electronic configuration [Ne]3s23p3 and is comes from the fact that white phosphorus therefore formally similar to nitrogen. It is glows slightly in the dark as a result of a however very much more reactive than ni- chemical reaction with oxygen. The light trogen and is never found in nature in the comes from excited atoms produced di- uncombined state. Phosphorus is wide- rectly in the reaction – not from the heat spread throughout the world; economic produced. It is thus an example of chemi- sources are phosphate rock (Ca3(PO4)2) luminescence. There are also a number of and the apatites, variously occurring as biochemical examples termed biolumines- both fluoroapatite (3Ca3(PO4)2.CaF2) and cence; for example, phosphorescence is as chloroapatite (3Ca3(PO4)2CaCl2). sometimes seen in the sea from marine or- Guano formed from the skeletal phosphate ganisms, or on rotting wood from certain of fish in sea-bird droppings is also an im- fungi (known as ‘fox fire’). portant source of phosphorus. The largest amounts of phosphorus compounds produced are used as fertilizers, with the de- phosphoric(V) acid /fos-for-ik, -foh-rik/ tergents industry producing increasingly (orthophosphoric acid; H PO ) A white 3 4 large tonnages of phosphates. Phosphorus solid that can be made by reacting phos- is an essential constituent of living tissue phorus(V) oxide with water or by heating and bones, and it plays a very important yellow phosphorus with nitric acid. The part in metabolic processes and muscle ac- naturally occurring phosphates (or- tion. thophosphates, M PO ) are salts of phos- 3 4 The element is obtained industrially by phoric(V) acid. An aqueous solution of the reduction of phosphate rock using sand phosphoric(V) acid has a sharp taste and (SiO2) and coke (C) in an electric furnace. has been used in the manufacture of soft The phosphorus is distilled off as P mol- ° 4 drinks. At about 220 C phosphoric(V) ecules and collected under water as white acid is converted to pyrophosphoric acid phosphorus. (H4P2O7). Pure pyrophosphoric acid in the → 2Ca3(PO4)2 + 6SiO2 + 10C P4 + form of colorless crystals is made by warm- 6CaSiO3 + 10CO ing solid phosphoric(V) acid with phos- There are three common allotropes of phorus(III) chloride oxide. Metaphos- phosphorus and several other modifica- phoric acid is obtained as a polymer, tions of these, some of which have indefi- (HPO3)n, by heating phosphoric(V) acid to nite structures. The common forms are: 320°C. Both meta- and pyrophosphoric 1. white (or yellow) phosphorus (distilla- acids change to phosphoric(V) acid in tion of phosphorus; soluble in some or- aqueous solution; the change will take ganic solvents) place faster at higher temperatures. Phos- 2. red phosphorus (heat on white phospho- phoric(V) acid is tri-basic, forming three rus, insoluble in organic solvents) – series of salts with the anions H2PO4 , 3. black phosphorus (heat on white phos- 2– 3– HPO4 , and PO4 . These series of salts phorus under high pressures). are acidic, neutral, and alkaline respec- Phosphorus, being in group 15 is non- tively. The alkali metal phosphates (except metallic in character and has a sufficiently lithium phosphate) are soluble in water but high ionization potential for the chemistry other metal phosphates are insoluble. of bonds to phosphorus to be almost en-

212 phosphorus(V) chloride tirely covalent. Phosphorus compounds are exhibiting the ready expansion of the coor- formally P(III) and P(V) compounds. The dination number to six. In the solid state, + – element forms a hydride, PH3 (phosphine), (PCl5) is [PCl4] [PCl6] (the first tetrahe- which is analogous to ammonia, but it is dral, the second octahedral) obtained by not formed by direct combination. Phos- transfer of a chloride ion. phorus(V) hydrides are not known. Phosphorus interacts directly with sev- When phosphorus is burned in air the eral metals and metalloids to give: product is the highly hygroscopic white 1. Ionic phosphides such as Na3P, Ca3P2, solid P4O10 (commonly called phosphorus Sr3P2. pentoxide, P O ); this is the P(V) oxide. In 2 5 2. Molecular phosphides such as P4S3 and a limited supply of air the P(III) oxide, P4S5. P O (called phosphorus trioxide) contam- 4 6 3. Metallic phosphides such as Fe2P. inated with unreacted phosphorus is ob- Symbol: P; m.p. 44.1°C (white) 410°C tained. The oxides both react with water to (red under pressure); b.p. 280.5°C; r.d. form acids; 1.82 (white) 2.2 (red) 2.69 (black) (all at → P4O6 + 6H2O 20°C); p.n. 15; r.a.m. 30.973762. 4H3PO3 phosphorous acid → P4O10 + 2H2O phosphorus(III) bromide (phosphorus 4HPO3 metaphosphoric acid tribromide; PBr ) A colorless liquid made → 3 P4O10 + 6H2O by reacting phosphorus with bromine. It is 4H3PO4 orthophosphoric acid. readily hydrolyzed by water to phosphonic There are also many poly-phosphoric acid and hydrogen bromide. Phos- acids and salts with different ring sizes and phorus(III) bromide is important in or- different chain lengths. Pyrophosphoric ganic chemistry, being used to replace a acid is obtained by melting phosphoric hydroxyl group with a bromine atom. acid, further dehydration above 200°C leads to metaphosphoric acids, phosphorus(V) bromide (phosphorus 2H PO → H P O + H O 3 4 4 2 7 2 pentabromide; PBr ) A yellow crystalline H P O → 2HPO + H O 5 4 2 7 3 2 solid that sublimes easily. It can be made Polyphosphates with molecular weights by the reaction of bromine and phospho- from 1000 to 10 000 are industrially important in detergent formulations and the rus(III) bromide. Phosphorus(V) bromide lower members are used to complex metal is readily hydrolyzed by water to phos- ions (sequestration). phoric(V) acid and hydrogen bromide. Its Phosphorus forms the P(III) halides, main use is in organic chemistry to replace a hydroxyl group with a bromine atom. PX3, with all the halogens, and P(V) halides, PX5, with X = F, Cl, Br. The P(III) halides are formed by direct combination phosphorus(III) chloride (phosphorus but because of hazards in the reaction of trichloride; PCl3) A colorless liquid formed from the reaction of phosphorus phosphorus and fluorine, PF3 is prepared with chlorine. It is rapidly hydrolyzed by from PCl3 The P(III) halide molecules are all pyra- water to phosphonic acid and hydrogen chloride. Phosphorus(III) chloride is used midal (as is PH3) and are readily hydrolyzed. The P(V) halides are also readily in organic chemistry to replace a hydroxyl hydrolyzed by water in two stages giving group with a chlorine atom. first the oxyhalide, then phosphoric acid, → PX5 + H2O POX3 + 2HX phosphorus(V) chloride (phosphorus → POX3 + 3H2O H3PO4 + 3HX pentachloride; PCl5) A white easily sub- In the gas phase the trihalides are pyra- limed solid formed by the action of chlo- midal and the pentahalides are trigonal rine on phosphorus(III) chloride. It is bipyramids. However, in tetrachloro- hydrolyzed by water to phosphoric(V) acid methane solution phosphorus pentachlo- and hydrogen chloride. Its main use is as a ride is a dimer with two chlorine bridges chlorinating agent in organic chemistry to

213 phosphorus(III) chloride oxide replace a hydroxyl group with a chlorine phosphorus oxychloride /oks-ă-klor-ÿd, atom. -kloh-rÿd/ See phosphorus(III) chloride oxide. phosphorus(III) chloride oxide (phosphorus trichloride oxide; phosphorus oxy- phosphorus pentabromide /pen-tă- chloride; phosphoryl chloride, POCl3) A broh-mÿd/ See phosphorus(V) bromide. colorless liquid that can be obtained by reacting phosphorus(III) chloride with oxy- phosphorus pentachloride /pen-tă-klor- gen or by distilling phosphorus(III) ÿd, -kloh-rÿd/ See phosphorus(V) chloride. chloride with potassium chlorate. The reactions of phosphorus(III) chloride oxide phosphorus pentoxide /pen-toks-ÿd/ See are similar to those of phosphorus(III) phosphorus(V) oxide. chloride. The chlorine atoms can be replaced by alkyl groups using Grignard phosphorus tribromide /trÿ-broh-mÿd/ reagents or by alkoxo groups using alco- See phosphorus(III) bromide. hols. Water hydrolysis yields phosphoric(V) acid. Phosphorus(III) chloride phosphorus trichloride /trÿ-klor-ÿd, oxide forms complexes with many metal -kloh-rÿd/ See phosphorus(III) chloride. ions. phosphorus trichloride oxide /trÿ-klor- phosphorus(III) hydride See phosphine. ÿd, -kloh-rÿd/ See phosphorus(III) chloride oxide. phosphorus(III) oxide (phosphorus trioxide; P2O3) A white waxy solid with a phosphorus trioxide /trÿ-oks-ÿd/ See characteristic smell of garlic; it usually ex- phosphorus(III) oxide. ists as P4O6 molecules. It is soluble in organic solvents, such as benzene and carbon phosphoryl chloride /fos-fŏ-răl, fos-for- disulfide, and is made by burning phos- ăl, -foh-răl/ See phosphorus(III) chloride phorus in a limited supply of air. Phospho- oxide. rus(III) oxide oxidizes in air to phosphorus(V) oxide at room temperature phot /foht, fot/ A unit of illumination in and inflames above 70°C. It dissolves the c.g.s. system, equal to an illumination slowly in cold water or dilute alkalis to give of one lumen per square centimeter. It is phosphonic acid or one of its salts. Phos- 4 phorus(III) oxide reacts violently with hot equal to 10 lx. water to form phosphine and phosphoric(V) acid. photochemical reaction /foh-toh-kem-ă- kăl/ A reaction brought about by light; ex- phosphorus(V) oxide (phosphorus pen- amples include the bleaching of colored material, the reduction of silver halides, toxide; P2O5) A white powder that is soluble in organic solvents. It usually exists as and the photosynthesis of carbohydrates. Chemical changes only occur when the re- P4O10 molecules. Phosphorus(V) oxide can be prepared by burning phosphorus in a acting atoms or molecules absorb photons plentiful supply of oxygen. It readily com- of the appropriate energy. The amount of bines with water to form phosphoric(V) substance that reacts is proportional to the acid and is therefore used as a drying agent quantity of energy absorbed. For example, for gases. It is a useful dehydrating agent in the reaction between hydrogen and chlo- because it is able to remove the elements of rine, it is not the concentrations of hydro- water from certain oxyacids and other gen or chlorine that dictate the rate of compounds containing oxygen and hydro- reaction but the intensity of the radiation. gen; for example, it reacts with nitric acid (HNO3) to give nitrogen pentoxide (N2O5) photochemistry /foh-toh-kem-iss-tree/ on heating. The branch of chemistry dealing with reac-

214 physisorption tions induced by light or ultraviolet radia- photoemission /foh-toh-i-mish-ŏn/ The tion. emission of photoelectrons by the photoelectric effect or by photoionization. photoelectric effect The emission of electrons from a solid (or liquid) surface photoionization /foh-toh-ÿ-ŏ-ni-zay- when it is irradiated with electromagnetic shŏn/ The ionization of atoms or mole- radiation. For most materials the photo- cules by electromagnetic radiation. electric effect occurs with ultraviolet radia- Photons absorbed by an atom may have tion or radiation of shorter wavelength; sufficient photon energy to free an electron some show the effect with visible radiation. from its attraction by the nucleus. The In the photoelectric effect, the number process is M + hv → M+ + e– of electrons emitted depends on the inten- As in the photoelectric effect, the radia- sity of the radiation and not on its fre- tion must have a certain minimum thresh- quency. The kinetic energy of the electrons old frequency. The energy of the that are ejected depends on the frequency photoelectrons ejected is given by W = hv – of the radiation. This was explained, by I, where I is the ionization potential of the Einstein, by the idea that electromagnetic atom or molecule. Analysis of the energies radiation consists of streams of photons. of the emitted electrons gives information The photon energy is hv, where h is the on the ionization potentials of the sub- Planck constant and v the frequency of the stance – a technique known as photoelec- radiation. To remove an electron from the tron spectroscopy. solid a certain minimum energy must be supplied, known as the work function, φ. photolysis /fŏ-tol-ă-sis/ A chemical reac- Thus, there is a certain minimum threshold tion that is produced by electromagnetic frequency v0 for radiation to eject elec- radiation (light or ultraviolet radiation). θ trons: hv0 = . If the frequency is higher Many photolytic reactions involve the for- than this threshold the electrons are mation of free radicals. ejected. The maximum kinetic energy (W) of the electrons is given by Einstein’s equa- photosynthesis /foh-tŏ-sin-th’ĕ-sis/ The tion: photochemical process green plants use to W = hv – φ synthesize organic compounds from car- The photoelectric effect also occurs bon dioxide and water. with gases. See photoionization. phthalic acid /thal-ik, fthal-ik/ See ben- photoelectrochemical cell /foh-toh-i- zene-1,2-dicarboxylic acid. lek-troh-kem-ă-kăl/ (PEC) A type of phthalic anhydride See benzene-1,2-di- voltaic cell in which one of the electrodes is carboxylic acid. a light-sensitive semiconductor (such as gallium arsenide). A current is generated physical change A change to a substance by light falling on the semiconductor, caus- that does not alter its chemical properties. ing electrons to pass between the electrode Physical changes (e.g. melting, boiling, and and the electrolyte and produce chemical dissolving) are comparatively easy to re- reactions in the cell. verse. photoelectron /foh-toh-i-lek-tron/ An physical chemistry The branch of chem- electron ejected from a solid, liquid, or gas istry concerned with physical properties of by the photoelectric effect or by photoion- compounds and how these depend on the ization. chemical bonding. photoelectron spectroscopy See pho- physisorption /fiz-ă-sorp-shŏn, -zorp-/ toionization. See adsorption.

215 piano-stool compound piano-stool compound See sandwich pitchblende /pich-blend/ (uraninite) A compound. black mineral consisting mostly of uranium(VI) oxide, UO3. It is the chief ore of pi bond See orbital. uranium and radium. pico- /pÿ-koh/ Symbol: p A prefix denot- pK The logarithm to the base 10 of the ing 10–12. For example, 1 picofarad (pF) = reciprocal of an acid’s dissociation con- 10–12 farad (F). stant: log10(1/Ka) pi complex A complex in which the metal ion is bound to a pi-electron system, as in Planck constant /plank/ Symbol: h A FERROCENE and ZEISE’S SALT. fundamental constant; the ratio of the energy (W) carried by a photon to its fre- picrate /pik-rayt/ A salt of PICRIC ACID; quency (v). A basic relationship in the metal picrates are explosive. quantum theory of radiation is W = hv. The value of h is 6.626 196 × 10–34 J s. The picric acid /pik-rik/ (2,4,6-trinitrophenol; Planck constant appears in many relation- ships in which some observable measure- C6H2(NO3)3OH) A yellow crystalline solid made by nitrating phenolsulfonic ment is quantized (i.e. can take only acid. It is used as a dye and as an explosive. specific discrete values rather than any of a With aromatic hydrocarbons picric acid range of values). The constant is named for forms characteristic charge-transfer com- the German physicist Max Planck plexes (misleadingly called picrates), used (1858–1947). in analysis for identifying the hydrocarbon. plane polarization A type of polarization of electromagnetic radiation in which pig iron The crude iron produced from a the vibrations take place entirely in one blast furnace, containing carbon, silicon, plane. and other impurities. The molten iron is run out of the furnace into channels (called plasma /plaz-mă/ A mixture of ions and ‘sows’), which branch out into a number of electrons, as in an electrical discharge. offshoots (called ‘pigs’) in which the metal Sometimes, a plasma is described as a is allowed to cool. fourth state of matter. pigment An insoluble, particulate color- plaster of Paris See calcium sulfate. ing material. plasticizer /plas-tă-sÿ-zer/ A substance pine-cone oil See turpentine. added to a synthetic resin to make it more flexible. pi orbital See orbital. plastics A common term for synthetic pipette /pi-pet/ A device used to transfer a polymers, especially when mixed with known volume of solution from one con- other substances such as plasticizers, tainer to another; in general, several sam- fillers, preservatives, and colorants. ples of equal volume are transferred for individual analysis from one stock solu- platinic chloride /plă-tin-ik/ See chloro- tion. Pipettes are of two types, bulb platinic acid. pipettes, which transfer a known and fixed volume, and graduated pipettes, which can platinum /plat-ă-nŭm/ A silvery-white transfer variable volumes. Pipettes were at malleable ductile transition metal. It occurs one time universally mouth-operated but naturally in Australia and Canada, either safety pipettes using a plunger or rubber free or in association with other platinum bulb are now preferred. metals. It is resistant to oxidation and is

216 polar bond not attacked by acids (except aqua regia) and platinum (Pt). They are sometimes or alkalis. Platinum is used as a catalyst for classed together as they have related prop- ammonia oxidation (to make nitric acid) erties and compounds. and in catalytic converters. It is also used in jewelry. Plexiglas /pleks-ă-glass/ (Trademark) A Symbol: Pt; m.p. 1772°C; b.p. 3830 ± widely-used acrylic resin, polymethyl- 100°C; r.d. 21.45 (20°C); p.n. 78; r.a.m. methacrylate. 195.08. plumbane /plum-bayn/ (lead(IV) hydride; platinum black A finely divided black PbH4) A colorless unstable gas that can be form of platinum produced, as a coating, obtained by the action of acids on a mix- by evaporating platinum onto a surface in ture of magnesium and lead pellets. an inert atmosphere. Platinum-black coatings are used as pure absorbent electrode plumbic /plum-bik/ Designating a coatings in experiments on electric cells. lead(IV) compound. They are also used, like carbon-black coatings, to improve the ability of a surface to plumbous /plum-bŭs/ Designating a absorb radiation. lead(II) compound. platinum(II) chloride (PtCl2) A gray- plutonium /ploo-toh-nee-ŭm/ A radioac- brown powder prepared by the partial de- tive silvery element of the actinoid series of composition of platinum(IV) chloride. It metals. It is a transuranic element found on may also be prepared by passing chlorine Earth only in minute quantities in uranium over heated platinum. Platinum(II) chlo- ores but readily obtained, as 239Pu, by neu- ride is insoluble in water but dissolves in tron bombardment of natural uranium. concentrated hydrochloric acid to form a The readily fissionable 239Pu is a major nu- complex acid. clear fuel and nuclear explosive. Plutonium is highly toxic because of its radioactivity; platinum(IV) chloride (PtCl4) A reddish in the body it accumulates in bone. hygroscopic solid prepared by the action of Symbol: Pu; m.p. 641°C; b.p. 3232°C; heat on chloroplatinic acid. Crystals of the r.d. 19.84 (25°C); p.n. 94; most stable iso- 244 × 7 pentahydrate, PtCl4.5H2O, are formed; an- tope Pu (half-life 8.2 10 years). hydrous platinum(IV) chloride is prepared by treating the hydrated crystals with con- PM See particulate matter. centrated sulfuric acid. The chloride dissolves in water to produce a strongly acidic point defect See defect. solution. Platinum(IV) chloride forms a series of hydrates having 1, 2, 4, and 5 mol- poison 1. A substance that destroys cata- ecules of water; the tetrahydrate is the most lyst activity. stable. The strongly acidic solution pro- 2. Any substance that endangers biological duced on dissolving in water probably con- activity, whether by physical or chemical tains H2[PtCl4(OH)2]. means. platinum–iridium An alloy of platinum polar Describing a compound with mol- containing up to 30% iridium. Hardness ecules that have a permanent dipole mo- and resistance to chemical attack increase ment. Hydrogen chloride and water are as the iridium content is increased. It is examples of polar compounds. used in jewelry, electrical contacts, and hy- podermic needles. polar bond A covalent bond in which the bonding electrons are not shared equally platinum metals The group of transition between the two atoms. A bond between metals ruthenium (Ru), osmium (Os), two atoms of different electronegativity is rhodium (Rh), iridium (Ir), palladium (Pd), said to be polarized in the direction of the

217 polarimeter more electronegative atom, i.e. the elec- tion. On reflection or on transmission trons are drawn preferentially towards the through certain substances (e.g. Polaroid) atom. This leads to a small separation of the field is confined to a single plane. The charge and the development of a bond DI- radiation is then said to be plane-polarized. POLE MOMENT as in, for example, hydrogen If the tip of the electric vector describes a fluoride, represented as H→F or as Hδ+–Fδ– circular helix as the wave propagates, the (F is more electronegative). light is said to be circularly polarized. The charge separation is much smaller 2. See polarizability. than in ionic compounds; molecules in 3. The reduction of current in a voltaic cell, which bonds are strongly polar are said to caused by the build-up of products of the display partial ionic character. The effect chemical reaction. Commonly, the cause is of the electronegative element can be trans- the build-up of a layer of bubbles (e.g. of mitted beyond adjacent atoms, thus the hydrogen). This reduces the effective area C–C bonds in, for example, CCl3CH3 and of the electrode, causing an increase in the CH3CHO are slightly polar. See also inter- cell’s internal resistance. It can also pro- molecular forces. duce a back e.m.f. Often a substance such as manganese(IV) oxide (a depolarizer) is polarimeter /poh-lă-rim-ĕ-ter/ (polar- added to prevent hydrogen build-up. iscope) An instrument for measuring OPTI- CAL ACTIVITY. polar molecule A molecule in which the individual polar bonds are not perfectly polarizability /poh-lă-rÿ-ză-bil-ă-tee/ The symmetrically arranged and are therefore ease with which an electron cloud is denot ‘in balance’. Thus the charge separa- formed (polarized). In ions, an increase in tion in the bonds gives rise to an overall size or negative charge leads to an increase charge separation in the molecule as for ex- in polarizability. The concept is of particu- ample, in water. Such molecules possess a lar use in the treatment of covalent contri- dipole moment. butions to predominantly ionic bonds embodied in Fajans’ Rules. Thus ions, such polarography /poh-lă-rog-ră-fee/ An an- as I–, Se2–, Te2–, are especially prone to co- alytical method in which current is mea- valent character, particularly in combina- sured as a function of potential. A special tion with ions of small size and high type of cell is used in which there is a small positive charge (i.e. high ionic potential). easily polarizable cathode (the dropping Molecular polarizability is a measure of mercury electrode) and a large non-polar- the ease with which electrons in the mole- izable anode (reference cell). The analytical cule are deformed, particularly by electro- reaction takes place at the cathode and is magnetic radiation. essentially a reduction of the cations, which are discharged according to the polarization /poh-lă-ri-zay-shŏn/ 1. The order of their electrode potential values. restriction of the vibrations in a transverse The data is expressed in the form of a po- wave so that the vibration occurs in a sin- larogram, which is a plot of current against gle plane. Electromagnetic radiation, for applied voltage. As the applied potential is instance, is a transverse wave motion. It increased a point is reached at which the can be thought of as an oscillating electric ion is discharged. There is a step-wise in- field and an oscillating magnetic field, both crease in current, which levels off because at right angles to the direction of propaga- of polarization effects. The potential at tion and at right angles to each other. Usu- half the step height (called the half-wave ally, the electric vector is considered since it potential) is used to identify the ion. Most is the electric field that interacts with elements can be determined by polarogra- charged particles of matter and causes the phy. The optimum concentrations are in effects. In ‘normal’ unpolarized radiation, the range 10–2–10–4M; modified tech- the electric field oscillates in all possible di- niques allow determinations in the parts rections perpendicular to the wave direc- per million range.

218 polychlorinated biphenyl polar solvent See solvent. In the sea, oil spillage from tankers and the inadequate discharge of sewage effluent pollution Any damaging or unpleasant are the main problems. change in the environment that results Other forms of pollution are noise from from the physical, chemical, or biological aircraft, traffic, and industry and the dis- side-effects of human industrial or social posal of radioactive waste. activities. Pollution can affect the atmosphere, rivers, seas, and the soil. polonium /pŏ-loh-nee-ŭm/ A radioactive Air pollution is caused by the domestic metallic element belonging to group 16 of and industrial burning of carbonaceous the periodic table. It occurs in very minute fuels, by industrial processes, and by car quantities in uranium ores. Over 30 ra- exhausts. Among recent problems are in- dioisotopes are known, nearly all alpha- dustrial emissions of sulfur(IV) oxide caus- particle emitters. Polonium is a volatile ing acid rain, and the release into the metal and evaporates with time. It is also atmosphere of chlorofluorocarbons, used strongly radioactive; a quantity of polo- in refrigeration, aerosols, etc., has been nium quickly reaches a temperature of a linked to the depletion of ozone in the few hundred degrees C because of the stratosphere. Carbon dioxide, produced by alpha emission. For this reason it has been burning fuel and by car exhausts, is slowly used as a lightweight heat supply in space building up in the atmosphere, which satellites. could result in an overall increase in the Symbol: Po; m.p. 254°C; b.p. 962°C; temperature of the atmosphere (green- r.d. 9.32 (20°C); p.n. 84; stablest isotope house effect). Car exhausts also contain 209Po (half-life 102 years). carbon monoxide and lead. The former has not yet reached dangerous levels, but vege- polyamide /pol-ee-am-ÿd, -id/ A synthetic tation near main roads contains a high pro- polymer in which the monomers are linked portion of lead and levels are sufficiently by the group –NH–CO–. Nylon is an ex- high in urban areas to cause concern about ample of a polyamide. the effects on children. Lead-free gasoline is available. Photochemical smog, caused polyatomic /pol-ee-ă-tom-ik/ Describing by the action of sunlight on hydrocarbons a molecule (or ion or radical) that consists and nitrogen oxides from car exhausts, is a of several atoms (three or more). Examples problem in several countries. Catalytic are benzene (C6H6) and methane (CH4). converters reduce harmful emissions from car exhausts. polybasic /pol-ee-bay-sik/ Describing an Water pollutants include those that are acid that has two or more replaceable hy- biodegradable, such as sewage effluent, drogen atoms. For example, phospho- which cause no permanent harm if ade- rus(V) acid, H3PO4, is tribasic. quately treated and dispersed, as well as those which are nonbiodegradable, such as polycarbonate /pol-ee-kar-bŏ-nayt/ A certain chlorinated hydrocarbon pesticides thermoplastic polymer consisting of poly- (e.g. DDT) and heavy metals, such as lead, esters of carbonic acid and dihydroxy com- copper, and zinc in some industrial efflu- pounds. They are tough and transparent, ents (causing heavy-metal pollution). used for making soft-drink bottles and When these accumulate in the environment electrical connectors. they can become very concentrated in food chains. The pesticides DDT, aldrin, and polychlorinated biphenyl /pol-ee-klor-ă- dieldrin are now banned in many coun- nay-tid, -kloh-ră- / (PCB) A type of com- tries. Water supplies can become polluted pound based on biphenyl (C6H5C6H5), in by leaching of nitrates from agricultural which some of the hydrogen atoms have land. The discharge of waste heat can cause been replaced by chlorine atoms. They are thermal pollution of the environment, but used in certain polymers used for electrical this is reduced by the use of cooling towers. insulators. PCBs are highly toxic and con-

219 polychloroethene cern has been caused by the fact that they thetic materials (e.g. nylon or polyethene). can accumulate in the food chain. The two major classes of synthetic polymers are thermosetting, which harden irre- polychloroethene /pol-ee-klor-oh-eth- versibly with increased temperature (e.g. een, -kloh-roh-/ (polyvinyl chloride; PVC) Bakelite), and thermoplastic, which soften A synthetic polymer made from on heating (e.g. polyethene). See also polychloroethene. It is a strong material with a merization. wide variety of uses. polymerization /pol-i-mer-i-zay-shŏn/ polycrystalline /pol-ee-kris-tă-lin, -lÿn/ The process in which one or more com- Describing a substance composed of very pounds react to form a POLYMER. Ho- many minute interlocking crystals that mopolymers are formed by polymerization have solidified together. of one monomer (e.g. the formation of polyethene from ethene). Heteropolymers polycyclic /pol-ee-sÿ-klik/ Describing a or copolymers come from two or more compound that has two or more rings in its monomers (e.g. the production of NYLON). molecules. Heteropolymers may be of different types depending on the arrangement of units. An polydioxoboric(III) acid /pol-ee-dÿ-oks- alternating copolymer of two units A and B oh-bô-rik/ See boric acid. has an arrangement: –A–B–A–B–A–B– pol-ee-een polyene / / An alkene with more A block copolymer has an arrangement in than two double bonds in its molecules. which blocks of one monomer alternate with blocks of the other; for example: polyester /pol-ee-es-ter/ A synthetic poly- –A–A–A–B–B–B–A–A–A– mer made by reacting alcohols with acids, In a graft copolymer there is a main choice so that the monomers are linked by the of one monomer (–A–A–A–A–), with short group –O–CO–. Synthetic fibers such as side chains of the other monomer attached Dacron are polyesters. at regular intervals (–B–B–). polyethene /pol-ee-eth-een/ (polyethylene; Stereospecific polymers have the sub- polythene) A synthetic polymer made from unit repeated along the chain in a regular ethene. It is produced in two forms – a soft way. These are tactic polymers. If one par- material of low density and a harder, ticular group is always on the same side of higher density form, which is more rigid. It the chain, the polymer is said to be isotac- can be made by the Ziegler process. tic. If the group alternates in position along the chain the polymer is syndiotactic. If polyethylene /pol-ee-eth-ă-leen/ See poly- there is no regular pattern, the polymer is ethene. atactic. Polymerization reactions are also classi- polyhydric alcohol /pol-ee-hÿ-drik/ An fied according to the type of reaction. Ad- alcohol that has several –OH groups in its dition polymerization occurs when the molecules. monomers undergo addition reactions, with no other substance formed. Conden- polymer /pol-i-mer/ A compound com- sation polymerization involves the elimina- posed of very large molecules made up of tion of small molecules in formation of the repeating molecular units (monomers). A polymer. See also cross linkage. polymer has a repeated structural unit, known as a mer. Polymers do not usually polymethanal /pol-ee-meth-ă-nal/ See have a definite relative molecular mass, as methanal. there are variations in the lengths of different chains. They may be natural substances polymethylmethacrylate /pol-ee-meth- (e.g. polysaccharides or proteins) or syn- ăl-meth-ak-ră-layt/ See Plexiglas.

220 polyvinyl ethanoate

HHH HHH HHH HHH

HHH H X H X XXX X H X H isotactic syndiotactic

Addition polymers

polymorphism /pol-ee-mor-fiz-ăm/ The and cellulose. See also carbohydrates; ability of certain chemical substances to sugar. exist in more than one physical form. For elements this is called allotropy. The exis- polystyrene /pol-ee-stÿ-reen/ A synthetic tence of two forms is called dimorphism. polymer made from styrene Crystalline structures of compounds can (phenylethene). Expanded polystyrene is a vary with temperature as a result of differ- rigid foam used in packing and insulation. ent packing arrangements of the particles. There is a transition temperature between polytetrafluoroethene /pol-ee-tet-ră- two forms and usually a marked change in floo-ŏ-roh-eth-een/ (PTFE) A synthetic density. polymer made from tetrafluoroethene (i.e. CF2:CF2). It is able to withstand high tem- polynucleotide /pol-ee-new-klee-ŏ-tÿd/ peratures without decomposing and also See nucleotide. has a very low coefficient of friction, hence its use in non-stick pans, bearings, etc. polypeptide /pol-ee-pep-tÿd, -tid/ A PEP- TIDE composed of a large number of polyunsaturated /pol-ee-ŭn-sach-ŭ-ray- amino-acid units. PROTEINS are polypep- tid/ Describing a compound that has a tides containing a few hundred amino-acid number of C=C bonds in its compounds. units. polyurethane /pol-ee-yoor-ă-thayn/ A polypropene /pol-ee-proh-peen/ (poly- synthetic polymer containing the group propylene) A synthetic polymer made –NH–CO–O– linking the monomers. from propene. It is similar in properties to Polyurethanes are made by condensation polythene, but stronger and lighter. The of isocyanates (–NCO) with alcohols. propene is polymerized by the Ziegler process. polyvalent /pol-ee-vay-lĕnt, pŏ-liv-ă-/ De- scribing an atom or group that has a va- polypropylene /pol-ee-proh-pă-leen/ See lence of more than one. polypropene. polyvinyl acetate /pol-ee-vÿ-năl/ (PVA; polysaccharide /pol-ee-sak-ă-rÿd, -rid/ polyvinyl ethanoate) A thermoplastic High-molecular-weight polymers of the polymer made by the polymerization of monosaccharides or sugars. They contain vinyl ethanoate, CH2:CHOOCH3. It is many repeated units in their molecular used as a coating for paper and cloth and structures. They can be broken down to in adhesives. smaller polysaccharides, disaccharides, and monosaccharides by hydrolysis or by polyvinyl chloride See polychloroethene. the appropriate enzyme. Important polysaccharides are heparin, inulin, starch, polyvinyl ethanoate See polyvinyl ac- glycogen (also known as animal starch), etate.

221 porcelain porcelain /por-sĕ-lin, pohr-/ A ceramic its compounds is very similar to that of the traditionally made from feldspar, kaolin other group 1 elements. (China clay), marble, and quartz. Particular points of distinction from sodium are: porphyrins /por-fă-rinz/ Cyclic organic 1. Burning in air produces the superoxide structures that have the important charac- KO2. teristic property of forming complexes 2. Because of the larger size of the K+ ion with metal ions. Examples of such metallo- and hence lower lattice energies, potas- porphyrins are the iron porphyrins (e.g. sium salts are often more soluble than heme in hemoglobin) and the magnesium corresponding sodium salts. porphyrin, chlorophyll, the photosynthetic 3. Potassium salts are usually less heavily pigment in plants. In nature, the majority hydrated than corresponding sodium of metalloporphyrins are conjugated to salts. proteins to form a number of very impor- The most abundant isotope of potas- tant molecules, e.g. hemoglobin, myoglo- sium is 39K (93.1%), with 41K also a stable bin, and the cytochromes. isotope (6.8%), but there is a naturally occurring radioactive isotope 40K (0.11%). potash See potassium carbonate; potas- Like sodium, potassium forms a num- sium hydroxide. ber of ionic alkyl- and aryl- derivatives of the type RK. potash alum See alum; aluminum potas- Symbol: K; m.p. 63.65°C; b.p. 774°C; sium sulfate. r.d. 0.862 (20°C); p.n. 19; r.a.m. 39.0983. potassamide /pŏ-tass-ă-mÿd/ See potas- potassium–argon dating A technique sium monoxide. for dating rocks. It depends on the radioactive decay of the radioisotope 40K to potassium /pŏ-tass-ee-ŭm/ A soft reactive 40Ar (half-life 1.27 × 1010 years) and is metal; the third member of the alkali met- based on the assumption that argon has als (group 1 of the periodic table). The been trapped in the rock since the time that atom has the argon electronic configura- the rock cooled (i.e. since it formed). If the tion plus an outer 4s1 electron. The element ratio 40Ar/40K is measured it is possible to gives a distinct lilac color to flames but, estimate the age of the rock. See also ra- due to the intense yellow coloration from dioactive dating. any trace impurity of sodium, the flame must be viewed through a cobalt glass. The potassium bicarbonate See potassium ionization potential is low and the chem- hydrogencarbonate. istry of potassium is largely the chemistry of the K+ ion. Potassium accounts for 2.4% potassium bromide (KBr) A white solid of the lithosphere and occurs in large salt that is extremely soluble in water. It is deposits such as carnallite formed by the action of bromine on hot (KCl.MgCl2.6H2O) and arcanite (K2SO4). potassium hydroxide solution or by the Large amounts also occur in mineral forms neutralization of the carbonate with hy- that are not of much use for recovery of drobromic acid. Potassium bromide forms potassium, e.g., orthoclase, K2Al2Si6O10. colorless cubic crystals. It is used exten- The commercial usage of potassium is sively in the manufacture of photographic much smaller than that of sodium; indus- plates, films, and papers and (formerly) as trially the element is obtained by electroly- a sedative in medicine. sis of the fused hydroxide. Potassium hydroxide is obtained by electrolysis of potassium carbonate (pearl ash; potash; carnallite solutions (the magnesium is ini- K2CO3) A white deliquescent solid manu- tially precipitated as Mg(OH)2), and both factured from potassium chloride by the hydrogen and chlorine are recovered as by- Leblanc process or, more often, using the products. The chemistry of potassium and Precht process. It cannot be made by the

222 potassium hydrogentartrate

Solvay process. In the laboratory, it can be potassium cyanide (KCN) A white ionic prepared by thermal decomposition of solid that is very soluble in water and ex- potassium hydrogencarbonate. Potassium tremely poisonous. It is made industrially carbonate is very soluble in water, its solu- by the Castner process and is used as a tions being strongly alkaline due to salt hy- source of cyanide and hydrocyanic acid. drolysis. It is used in the laboratory as a Aqueous solutions of potassium cyanide drying agent and industrially in the manu- are strongly hydrolyzed, the solutions facture of soft soap, hard glass, and in the being alkaline. On standing, these solu- dyeing industry. Potassium carbonate crys- tions slowly evolve hydrocyanic acid. tallizes out between 10 and 25°C as ° K2CO3.3H2O; it dehydrates at 100 C to potassium dichromate (K Cr O ) An ° 2 2 7 K2CO3.H2O and at 130 C to K2CO3. orange-red solid prepared by adding potassium chloride solution to a concentrated potassium chlorate (KClO3) A white solution of sodium dichromate and crystal- soluble solid prepared by the electrolysis of lizing out or by acidifying a solution of a concentrated solution of potassium chlo- potassium chromate and evaporating. It is ride. Industrially, it is prepared by the frac- less soluble than sodium dichromate in tional crystallization of a solution cold water but more soluble in hot water. containing sodium chlorate and potassium Potassium dichromate is used as an oxidiz- chloride. When heated, it decomposes to ing agent both in volumetric analysis and yield oxygen and potassium chloride. in organic chemistry. The crystals are tri- Potassium chlorate is a powerful oxidizing clinic, anhydrous, and non-deliquescent. agent and is used in explosives, matches, Addition of an alkali to a solution of the weedkillers, and fireworks, and as a disin- dichromate yields the chromate. fectant. It oxidizes iodide ions to iodine when in an acidic medium. When heated potassium hydride (KH) A white ionic just above its melting point, potassium per- solid prepared by passing hydrogen over chlorate is formed. heated potassium, the metal being suspended in an inert medium. It is an excel- potassium chloride (KCl) A white ionic solid prepared by neutralizing hydrochlo- lent reducing agent. ric acid with potassium hydroxide solution. Potassium chloride occurs naturally potassium hydrogencarbonate (potas- as the minerals sylvine and carnallite. It is sium bicarbonate; KHCO3) A white solid more soluble than sodium chloride in hot prepared by passing carbon dioxide water but less soluble in cold water. On through a saturated solution of potassium- evaporation of an aqueous solution color- carbonate. It occurs naturally in the min- less cubic crystals similar to those of eral calcinite. Potassium hydrogen sodium chloride are produced. Potassium carbonate is more soluble in water than chloride is used as a fertilizer and in the sodium hydrogencarbonate. When heated, manufacture of potassium hydroxide. it undergoes thermal decomposition to give the carbonate, water, and carbon dioxide. potassium chromate (K2CrO4) A bright The salt forms monoclinic crystals. Its so- yellow solid prepared by adding potassium lutions are strongly alkaline as a result of hydroxide solution to a solution of potas- salt hydrolysis. sium dichromate. It is extremely soluble in water. Addition of an acid to an aqueous potassium hydrogentartrate /hÿ-drŏ- solution of potassium chromate converts jĕn-tar-trayt/ (cream of tartar; – + the chromate ions into dichromate ions. HOOC(CHOH)2COO K ) A white crys- The salt is used as an indicator in silver ni- talline solid, an acid salt of tartaric acid trate titrations. The crystals are isomor- that occurs in grape juice. It is used as the phous with potassium sulfate. acid ingredient of BAKING POWDER.

223 potassium hydroxide potassium hydroxide (caustic potash; Potassium permanganate is used in volu- KOH) A white solid manufactured by the metric analysis as an oxidizing agent, as a electrolysis of potassium chloride solution bactericide, and as a disinfectant. In aque- in a mercury-cathode cell. It can also be ous solution its behavior as an oxidizing prepared by heating either potassium car- agent depends on the pH of the solution. bonate or potassium sulfate with slaked lime. The process closely resembles the potassium monoxide /mon-oks-ÿd, -id/ Gossage process for making sodium hy- (K2O) An ionic solid that is white when droxide. In the laboratory, it can be made cold and yellow when hot. It is prepared by by reacting potassium, potassium monox- heating potassium with potassium nitrate. ide, or potassium superoxide with water. Potassium monoxide dissolves violently in Potassium hydroxide resembles sodium hy- water to form potassium hydroxide solu- droxide but is more soluble in water and tion. The hydrate K2O.3H2O is known. alcohol. It is preferred to sodium hydrox- Potassium monoxide dissolves in liquid ide for the absorption of carbon dioxide ammonia with the formation of potassium and sulfur(IV) oxide because of its greater hydroxide and potassamide (KNH2). solubility. Potassium hydroxide is used as an electrolyte in the Ni–Fe electric storage potassium nitrate (saltpeter; niter; battery and in the production of soft soaps. KNO3) A white solid, soluble in water, It forms crystalline hydrates with 1, 1½, formed by fractional crystallization of and 2 molecules of water. sodium nitrate and potassium chloride solutions. It occurs naturally as niter (salt- potassium iodate /ÿ-ŏ-dayt/ (KIO3) A peter) in rocks in India, South Africa, and white solid formed either by adding iodine Brazil. When heated it decomposes to give to a hot concentrated solution of potas- the nitrite and oxygen. Unlike sodium ni- sium hydroxide or by the electrolysis of trate it is non-deliquescent. Potassium ni- potassium iodide solution. No hydrates are trate is used in gunpowder, fertilizers, and known. It is a source of iodide and iodic in the laboratory preparation of nitric acid. acid. When treated with a dilute acid and a reducing agent, the iodate ions are reduced potassium nitrite (KNO2) A creamy del- to iodine. iquescent solid that is readily soluble in water. It reacts with cold dilute mineral potassium iodide (KI) A white ionic acids to produce solutions of nitrous acid. solid readily soluble in water. It is prepared Potassium nitrite is used in organic chem- by dissolving iodine in hot concentrated istry in the process of diazotization. potassium hydroxide solution. Both the iodide and iodate are formed but the latter is potassium permanganate See potas- removed by fractional crystallization. sium manganate(VII). Potassium iodide has a sodium chloride cubic lattice. In solution with iodine it potassium sulfate (K2SO4) A white solid forms potassium tri-iodide. It is used in prepared by the neutralization of either medicine, particularly in the treatment of potassium hydroxide or potassium carbon- goiter resulting from iodine deficiency. Di- ate with dilute sulfuric acid. It occurs natu- lute acidified solutions of potassium iodide rally in Stassfurt deposits as schönite. can act as reducing agents, manganate(VII) Potassium sulfate is soluble in water, form- ions being reduced to manganese(II) ions, ing a neutral solution. It is used as a fertil- copper(II) ions to copper(I) ions, and io- izer and in the chemical industry in the date ions to iodine. preparation of alums. The anhydrous salt crystallizes in the rhombic form. potassium manganate(VII) (potassium permanganate; KMnO4) A purple solid potassium sulfide (K2S) A yellowish- soluble in water. It is prepared by oxidizing brown solid prepared by saturating an potassium manganate(VI) with chlorine. aqueous solution of potassium hydroxide

224 promoter with hydrogen sulfide and then adding an pressure = force/area equal volume of potassium hydroxide. In- The unit is the pascal (Pa). dustrially it is produced by heating potassium sulfate and carbon at high primary alcohol See alcohol. temperature. The sulfide crystallizes out from aqueous solution as K2S.5H2O. Its primary amine See amine. aqueous solutions undergo hydrolysis, the solution being strongly alkaline. primary cell A voltaic cell in which the chemical reaction that produces the e.m.f. potassium superoxide (K2O) A yellow is not reversible. Compare accumulator. paramagnetic solid prepared by burning potassium in excess oxygen. When treated primary standard A substance that can with cold water or dilute mineral acids, hy- be used directly for the preparation of stan- drogen peroxide is produced. If heated dard solutions without reference to some strongly, it yields oxygen and potassium other concentration standard. Primary monoxide. Potassium superoxide is a pow- standards should be easy to purify, dry, ca- erful oxidizing agent. pable of preservation in a pure state, unaffected by air or CO2, of a high molecular potassium thiocyanate /th’ÿ-oh-sÿ-ă- weight (to reduce the significance of weigh- nayt/ (KSCN) A colorless hygroscopic ing errors), stoichiometric, and readily sol- solid. Its solution is used in a test for uble. Any likely impurities should be easily iron(III) compounds, with which it turns a identifiable. blood-red color. prismane /priz-mayn/ See Ladenburg ben- potentiometric titration /pŏ-ten-shee-ŏ- zene. met-rik/ A titration in which an electrode is used in the reaction mixture. The end producer gas (air gas) A mixture of car- point can be found by monitoring the elec- bon monoxide (25–30%), nitrogen tric potential of this during the titration. (50–55%), and hydrogen (10–15%), prepared by passing air with a little steam praseodymium /pray-zee-oh-dim-ee-ŭm/ through a thick layer of white-hot coke in A soft ductile malleable silvery element of a furnace or ‘producer’. The air gas is used the lanthanoid series of metals. It occurs in while still hot to prevent heat loss and finds association with other lanthanoids. uses in industrial heating, for example the Praseodymium is used in several alloys, as firing of retorts and in glass furnaces. Com- a catalyst, and in enamel and yellow glass pare water gas. for eye protection. Symbol: Pr; m.p. 931°C; b.p. 3512°C; product See chemical reaction. r.d. 6.773 (20°C); p.n. 59; r.a.m. 140.91. proline /proh-leen, -lin/ See amino acids. precipitate /pri-sip-ă-tayt (vb.), pri-sip-ă- tayt, -tit (n.)/ A suspension of small parti- promethium /prŏ-mee-th’ee-ŭm/ A ra- cles of a solid in a liquid formed by a dioactive element of the lanthanoid series chemical reaction. of metals. It is not found naturally on Earth but can be produced artificially by the fis- precursor A substance from which an- sion of uranium. It is used in some minia- other substance is formed in a chemical re- ture batteries. action. Symbol: Pm; m.p. 1168°C; b.p. 2730°C (approx.); r.d. 7.22 (20°C); p.n. 61; sta- pressure Symbol: p The pressure on a sur- blest isotope 145Pm (half-life 18 years). face due to forces from another surface or from a fluid is the force acting at 90° to promoter (activator) A substance that unit area of the surface: improves the efficiency of a catalyst. It does

225 proof not itself catalyze the reaction but assists CH2OH) and propan-2-ol (CH3CH2- the catalytic activity. For example, alumina (OH)CH3). Both are colorless volatile or molybdenum promotes the catalytic ac- flammable liquids. tivity of finely divided iron in the Haber process. The manner in which a promoter propanone /proh-pă-nohn/ (acetone; functions is not fully understood; no one CH3-COCH3) A colorless liquid ketone, theory covers all the examples. See also used as a solvent and in the manufacture of coenzymes. methyl 2-methyl-propanoate (from which polymethylmethacrylate is produced). proof A measure of the ethanol content of Propanone is manufactured from propene, intoxicating drinks. In the United States, either by the air-oxidation of propan-2-ol proof spirit contains 40% ethanol by vol- or, as a by-product from the cumene ume. In the UK, it contains 49.28% of process. ethanol by weight (57.1% by volume at ° 16 C). The degree of proof gives the num- propenal /proh-pĕ-năl/ (acrolein; ber of parts of proof spirit per 100 parts of CH :CHCHO) A colorless liquid unsatu- ° 2 the total. 100 of proof is 50% by volume, rated aldehyde with a pungent odor. It can ° × 80 of proof is 0.8 50%, etc. be polymerized to make acrylate resins. propanal /proh-pă-nal/ (propionaldehyde; propene /proh-peen/ (propylene; C3H6) A C2H5CHO) A colorless liquid aldehyde. gaseous alkene. Propene is not normally present in the gaseous crude-oil fraction /proh-payn/ (C H ) A gaseous propane 3 8 but can be obtained from heavier fractions alkane obtained either from the gaseous by catalytic cracking. This is the principal fraction of crude oil or by the cracking of industrial source. Propene is the organic heavier fractions. The principal use of starting material for the production of propane is as a fuel for heating and cook- propan-2-ol, required for the manufacture ing, since it can be liquefied under pressure, of propanone (acetone), and the starting stored in cylinders, and transported easily. Propane is the third member of the ho- material for the production of polypropene mologous series of alkanes. (polypropylene). propanedioic acid /proh-payn-dÿ-oh-ik/ propenoate /proh-pĕ-nayt/ A salt or ester of propenoic acid. (malonic acid; CH2(COOH)2) A white crystalline dibasic carboxylic acid. propenoic acid /proh-pĕ-noh-ik/ (acrylic propane-1,2,3-triol (glycerol; glycerine; acid; CH2:CHCOOH) An unsaturated liquid carboxylic acid with a pungent odor. CH2(OH)CH(OH)CH2(OH)) A colorless viscous liquid obtained as a by-product The acid and its esters are used to make from the manufacture of soap by the reac- ACRYLIC RESINS. tion of animal fats with sodium hydroxide. It is used as a solvent and plasticizer. See propenonitrile /pro-pĕ-noh-nÿ-trăl, -tril, - also glyceride. trÿl/ (acrylonitrile; H2C:CH(CN)) An organic compound from which acrylic-type propanoate /proh-pă-noh-ayt, -it/ A salt polymers are produced. or ester of propanoic acid. propenyl group /proh-pĕ-năl/ (allyl propanoic acid /proh-pă-noh-ik/ (propi- group) The organic group, onic acid; C2H5COOH) A colorless liquid CH2=CH–CH2–, derived by removing one carboxylic acid. hydrogen atom from propene. propanol /proh-pă-nol, -nohl/ Either of propionaldehyde /proh-pee-ŏ-nal-dĕ- two alcohols: propan-1-ol (CH3CH2- hÿd/ See propanal. 226 pyrazine propionic acid /proh-pee-on-ik/ See pseudoaromatic /soo-doh-a-rŏ-mat-ik/ propanoic acid. See aromatic compound. propylene /proh-pă-leen/ See propene. pseudo-first order Describing a reaction that appears to exhibit first-order kinetics propyl group /proh-păl/ The group under special conditions, even though the CH3CH2CH2–. ‘true’ order is greater than one. For example, in the hydrolysis of an ester in the pres- protactinium /proh-tak-tin-ee-ŭm/ A ence of a large volume of water, the toxic radioactive element of the actinoid concentration of water remains approxi- series of metals. It occurs in minute quanti- mately constant. The rate of reaction is ties in uranium ores as a radioactive decay thus found experimentally to be propor- product of actinium. tional to the concentration of the ester only ° ° Symbol: Pa; m.p. 1840 C; b.p. 4000 C (even though it also depends on the (approx.); r.d. 15.4 (calc.); p.n. 91; most amount of water present). Such a reaction 231 stable isotope Pa (half-life 32 500 is described as ‘bimolecular of the first years). order’. /proh-teen, -tee-in/ A naturally oc- protein pseudohalogens /soo-doh-hal-ŏ-jĕnz/ A curring compound found in all living mat- small group of simple inorganic com- ter, consisting of AMINO ACIDS joined into pounds with symmetrical molecules that long chains by PEPTIDE links. The primary resemble the halogens in some reactions structure is the particular sequence of and compounds. For example, (CN) amino acids present. The protein also has a 2 (cyanogen) has compounds analogous to secondary structure, with the chains coiled halogen compounds (e.g. HCN, KCN, in a helix or held together in pleated sheets. The tertiary structure is the way in which CH3CN, etc.). Thiocyanogen, (SCN)2, is the chain or sheet is arranged in space. Sec- another example. ondary structures are held by hydrogen bonds between N–H and O=C groups. PTFE See polytetrafluoroethene. Tertiary structures are held by hydrogen bonds or cross linkages of the type –S–S– purine /pyoor-een, -in/ A simple nitroge- (cystine links). nous organic molecule with a double ring structure. Members of the purine group in- proton An elementary particle with a pos- clude adenine and guanine, which are con- itive charge (+1.602 192 × 10–19 C) and stituents of the nucleic acids, and certain rest mass 1.672 614 × 10–27 kg. Protons plant alkaloids, such as caffeine and theo- are nucleons, found in all nuclides. bromine. proton number (atomic number) Symbol: PVA See polyvinyl acetate. Z The number of protons in the nucleus of an atom. The proton number determines PVC See polychloroethene. the chemical properties of the element because the electron structure, which deter- pyranose /pÿ-ră-nohs, pi-ran-ohs/ A mines chemical bonding, depends on the SUGAR that has a six-membered ring form electrostatic attraction to the positively (five carbon atoms and one oxygen atom). charged nucleus. pyrazine /pÿ-ră-zeen, -zin/ (1,4-diazine; Prussian blue See cyanoferrate. C4H4N2) A heterocyclic aromatic compound with a six-membered ring contain- prussic acid /pruss-ik/ See hydrocyanic ing four carbon atoms and two nitrogen acid. atoms.

227 pyrazole pyrazole /pÿ-ră-zohl/ (1,2-diazole; pyrites /pÿ-rÿ-teez, pi-, pÿ-rÿts/ A mineral C3H4N2) A heterocyclic crystalline aro- sulfide of a metal; e.g. iron pyrites FeS2. matic compound with a five-membered ring containing three carbon atoms and pyrolusite /pÿ-rŏ-loo-sÿt/ See man- two nitrogen atoms. ganese(IV) oxide. pyrene /pÿ-reen/ (C16H10) A solid aro- pyrolysis /pÿ-rol-ă-sis, pi-/ The decompo- matic compound whose molecules consist sition of chemical compounds by subject- of four benzene rings joined together. It is ing them to very high temperature. carcinogenic. pyrometer /pÿ-rom-ĕ-ter, pi-/ An instru- Pyrex /pÿ-reks/ (Trademark) A particu- ment used in the chemical industry to mea- larly strong, heat resistant, and chemically sure high temperature, e.g. in reactor inert borosilicate glass commonly used for laboratory glassware. vessels. pyrone /pÿ-rohn, pi-rohn/ A compound pyridine /pi-ră-deen/ (C5H5N) An organic having a six-membered ring of five carbon liquid of formula C5H5N. The molecules have a hexagonal planar ring and are iso- atoms and one oxygen, with one of the car- electronic with benzene. Pyridine is an ex- bon atoms attached to a second oxygen in ample of an aromatic heterocyclic a carbonyl group. The pyrone ring system compound, with the electrons in the car- has two forms depending on the position of bon–carbon pi bonds and the lone pair of the carbonyl relative to the oxygen hetero the nitrogen delocalized over the ring of atom. It occurs in many natural products. atoms. The compound is extracted from coal tar and used as a solvent and as a raw pyrophoric /pÿ-rŏ-fô-rik, pi-/ 1. Describ- material for organic synthesis. ing a compound that ignites spontaneously in air. 2. Describing a metal or alloy that gives sparks when struck. (Lighter flints are made of pyrophoric alloy.)

pyrophosphoric acid /pÿ-roh-fos-fô-rik/ See phosphoric(V) acid.

N pyrosulfuric acid /pÿ-roh-sul-fyoor-ik/ Pyridine See oleum. pyrimidine /pi-rim-ă-deen, pi-ră-mă-/ A pyrrhole /pi-rohl/ ((CH)4NH) A hetero- simple nitrogenous organic molecule cyclic liquid aromatic compound with a whose ring structure is contained in the five-membered ring containing four carbon pyrimidine bases cytosine, thymine, and atoms and one nitrogen atom. It has im- uracil, which are constituents of the nucleic portant biochemical derivatives, including acids. chlorophyll and heme.

228 Q

quadrivalent /kwod-ră-vay-lĕnt, kwod- tum of electromagnetic radiation is the riv-ă-/ (tetravalent) Having a valence of photon. four. quantum electrodynamics The use of qualitative analysis /kwol-ă-tay-tiv/ quantum mechanics to describe how par- Analysis carried out with the purpose of ticles and electromagnetic radiation inter- identifying the components of a sample. act. Classical methods involved simple preliminary tests followed by a carefully devised quantum mechanics See quantum scheme of systematic tests and procedures. theory. Modern methods include the use of such techniques as infrared spectroscopy and quantum number An integer or half in- emission spectrography. Compare quanti- teger that specifies the value of a quantized tative analysis. physical quantity (energy, angular momentum, etc.). See atom; Bohr theory; spin. quanta /kwon-tă/ See quantum. quantum states States of an atom, elec- quantitative analysis /kwon-tă-tay-tiv/ tron, particle, etc., specified by a unique set Analysis carried out with the purpose of of quantum numbers. For example, the hy- determining the concentration of one or drogen atom in its ground state has an elec- more components of a sample. Classical tron in the K shell specified by the four wet methods include volumetric and gravi- quantum numbers: n = 1, l = 0, m = 0, ms = metric analysis. A wide range of more ½. In the helium atom there are two elec- modern instrumental techniques are also trons: ½ used, including polarography and various n = 1, l = 0, m = 0, ms = ½ types of chromatography and spec- n = 1, l = 0, m = 0, ms = – troscopy. Compare qualitative analysis. quantum theory A mathematical theory quantized /kwon-tÿzd/ Describing a phys- originally introduced by Max Planck ical quantity that can take only certain dis- (1900) to explain the radiation emitted crete values, and not a continuous range of from hot bodies. Quantum theory is based values. Thus, in an atom or molecule the on the idea that energy (or certain other electrons around the nucleus can have cer- physical quantities) can be changed only in tain energies, E1, E2, etc., and cannot have certain discrete amounts for a given sys- intermediate values. Similarly, in atoms tem. Other early applications were the ex- and molecules, the electrons have quan- planations of the photoelectric effect and tized values of spin angular momentum the Bohr theory of the atom. and orbital angular momentum. Quantum mechanics is a system of mechanics that developed from quantum the- quantum /kwon-tŭm/ (pl. quanta) A defi- ory and is used to explain the behavior of nite amount of energy released or absorbed atoms, molecules, etc. In one form it is in a process. Energy often behaves as if based on de Broglie’s idea that particles can it were ‘quantized’ in this way. The quan- have wavelike properties – this branch of

229 quantum yield quantum mechanics is called wave me- quenching A method used to alter the mechanics. See orbital. chanical properties of metals. Hot metal is lowered quickly into a bath of oil, water, quantum yield The average number of or brine and the rapid cooling results in a reactive events per absorbed photon in a fine grain structure. This treatment in- photochemical reaction. creases the hardness of a metal but often makes it brittle. quartz A natural crystalline form of silica (SiO2). quicklime See calcium oxide. quasicrystal /kway-zÿ-kris-tăl,-sÿ-, kwah- quinhydrone electrode /kwin-hÿ-drohn/ zee-, -see-/ A type of crystal structure in See quinone. which there is long-range order but in which the symmetry of the repeating unit is quinine /kwÿ-nÿn, kwi-neen/ A poisonous not one allowed in normal crystals. For ex- ALKALOID found in the bark of the cinchona ample, in three dimensions, it would be tree of South America. It is used in treating possible to form a crystal structure made malaria. up of cubes, but not one made by joining icosahedra. However, there are examples quinol /kwin-ol. -ohl/ See benzene-1,4- of solids, such as the compound AlMn, diol. that have icosahedral symmetry and a /kwin-ŏ-leen, -lin/ (C H N) A long-range repeating order in the stucture. quinoline 9 7 colorless two-ring heterocyclic compound These are known as quasicrystals. with an unpleasant odor, which acts as a base and forms salts with acids. First made quaternary ammonium compound A from the alkaloid quinine, it is found in compound formed from an amine by addi- bone oil and coal tar and used for making tion of a proton to produce a positive ion. drugs and dyestuffs. Quaternary compounds are salts, the simplest example being ammonium com- quinone /kwă-nohn, kwin-ohn/ (cyclo- pounds formed from ammonia and an hexadiene-1,4-dione; benzoquinone; acid, for example: C H O ) A yellow crystalline organic → + – 6 4 2 NH3 + HCl NH4 Cl compound with a pungent odor. Its mole- Other amines can also add protons to give cules contain a non-aromatic six-carbon analogous compounds. For instance, ring and it behaves as an unsaturated dike- methylamine (CH3NH2) forms the com- tone with conjugated double bonds. It is pound used in making dyestuffs. A platinum elec- + – [CH3NH3] X trode in an equimolar solution of quinone where X– is an acid radical. and hydroquinone (benzene-1,4-diol, The formation of quarternary com- C6H4(OH)2) is used as a standard electrode pounds occurs because the lone pair on the in electrochemistry. The reaction is: ˆ + nitrogen atom can form a coordinate bond C6H4(OH)2 C6H4O2 + 2H + 2e with a proton. This can also occur with This type of electrode is called a quinhy- heterogeneous nitrogen compounds, such drone electrode. as adenine, cytosine, thymine, and guanine. Such compounds are known as ni- quinquevalent /kwing-kwĕ-vay-lĕnt, trogenous bases. kwing-kwev-ă-/ See pentavalent.

230 R

racemate /ray-seem-ayt, -sem-, ră-/ See radioactivity /ray-dee-oh-ak-tiv-ă-tee/ optical activity. The disintegration or decay of certain unstable nuclides with emission of radiation. racemic mixture /ray-see-mik, ră-/ See The emission of alpha particles, beta parti- optical activity. cles, and gamma waves are the three most important forms of radiation that occur racemization /rass-ĕ-mi-zay-shŏn/ The during decay. conversion of an optical isomer into an equal mixture of isomers, which is not op- radiocarbon dating /ray-dee-oh-kar-bŏn/ tically active. See carbon dating. rad A unit of absorbed dose of ionizing ra- radiochemistry /ray-dee-oh-kem-iss-tree/ diation, defined as being equivalent to an The chemistry of radioactive isotopes of el- absorption of 10–2 joule of energy in one ements. Radiochemistry involves such top- kilogram of material. ics as the preparation of radioactive compounds, the separation of isotopes by radian Symbol: rad The SI unit of plane chemical reactions, the use of radioactive angle; 2π radian is one complete revolution labels in studies of mechanisms, and exper- (360°). iments on the chemical reactions and compounds of transuranic elements. radiation /ray-dee-ay-shŏn/ In general the emission of energy from a source, either as radiogenic /ray-dee-oh-jen-ik/ Caused by waves (light, sound, etc.) or as moving par- radioactive decay. ticles (beta rays or alpha rays). radioisotope /ray-dee-oh-ÿ-sŏ-tohp/ A radical /rad-ă-kăl/ A group of atoms in a radioactive isotope of an element. Tritium, molecule. See also free radical. for instance, is a radioisotope of hydrogen. Radioisotopes are extensively used in re- radioactive /ray-dee-oh-ak-tiv/ Describ- search as souces of radiation and as tracers ing an element or nuclide that exhibits nat- in studies of chemical reactions. Thus, if an ural radioactivity. atom in a compound is replaced by a radioactive nuclide of the element (a label) it radioactive dating (radiometric dating) is possible to follow the course of the A technique for dating archaeological spec- chemical reaction. Radioisotopes are also imens, rocks, etc., by measuring the extent used in medicine or diagnosis and treat- to which some radionuclide has decayed to ment. give a product. See carbon dating; potassium–argon dating; rubidium–strontium radiolysis /ray-dee-ol-ă-sis/ A chemical re- dating; uranium–lead dating. action produced by high-energy radiation (x-rays, gamma rays, or particles). radioactive decay series The series of definite isotopes to which a given radioac- radiometric dating /ray-dee-oh-met-rik/ tive element is transformed as it decays. See radioactive dating.

231 radio waves radio waves A form of ELECTROMAGNETIC Raney nickel /ray-nee/ A catalytic form RADIATION with wavelengths greater than a of nickel produced by treating a few millimeters. nickel–aluminum alloy with caustic soda. The aluminum dissolves (as aluminate) and radium /ray-dee-ŭm/ A white radioactive Raney nickel is left as a spongy mass, luminescent metallic element of the alka- which is pyrophoric when dry. It is used es- line-earth group. It has several short-lived pecially for catalyzing hydrogenation reac- radioisotopes and one long-lived isotope, tions. radium-226 (half-life 1602 years). Radium is found in uranium ores, such as the ox- Raoult’s law /rah-oolz/ A relationship be- ides pitchblende and carnotite. It was for- tween the pressure exerted by the vapor of merly used in luminous paints and a solution and the presence of a solute. It radiotherapy. states that the partial vapor pressure of a Symbol: Ra; m.p. 700°C; b.p. 1140°C; solvent above a solution (p) is proportional r.d. 5 (approx. 20°C); p.n. 88; r.a.m. to the mole fraction of the solvent in the so- 226.0254 (226Ra). lution (X) and that the proportionality constant is the vapor pressure of pure sol- radon /ray-don/ A colorless monatomic vent, (p0), at the given temperature: i.e. p = radioactive element of the rare-gas group, p0X. Solutions that obey Raoult’s law are now known to form unstable compounds. said to be ideal. There are some binary so- It has 19 short-lived radioisotopes; the lutions for which Raoult’s law holds over most stable, radon-222, is a decay product all values of X for either component. Such of radium-226 and itself disintegrates into solutions are said to be perfect and this bean isotope of polonium with a half-life of havior occurs when the intermolecular at- 3.82 days. 222Rn is sometimes used in ra- traction between molecules within one diotherapy. Radon occurs in uranium component is almost identical to the at- mines and is also detectable in houses built traction of molecules of one component for in certain areas of the country. molecules of the other (e.g. chlorobenzene Symbol: Rn; m.p. –71°C; b.p. –61.8°C; and bromobenzene). Because of solvation d. 9.73 kg m–3 (0°C); p.n. 86. forces this behavior is rare and in general Raoult’s law holds only for dilute solu- raffinate /raf-ă-nayt/ The liquid remain- tions. ing after the solvent extraction of a dis- For solutions that are ideal but not per- solved substance. See solvent extraction. fect the solute behavior is similar in that the partial pressure of the solute, ps, is pro- raffinose /raf-ă-nohs/ A SUGAR occurring portional to the mole fraction of the solute, in sugar beet. It is a trisaccharide consisting Xs, but in this case the proportionality con- of fructose, galactose, and glucose units. stant, p′, is not the vapor pressure of the pure solute but must be determined exper- r.a.m. See relative atomic mass. imentally for each system. This solute equivalent of Raoult’s law has the form ps ′ Raman effect /rah-măn/ A change in the = p Xs, and is called HENRY’S LAW. Because frequency of electromagnetic radiation of intermolecular attractions p′ is usually that occurs when a photon of radiation unless than p0. The law is named for the dergoes an inelastic collision with a mol- French chemist Françoise-Marie Raoult ecule. The effect was first observed by the (1830–1901). See also Babo’s law. Indian physicists Sir Chandrasekhara Venkata Raman (1888–1970) and his col- rare earths See lanthanoids. league Sir Kariamanikkam Srinivasa Krish- nan in 1928. It has been used extensively in rare gases (noble gases; inert gases; group Raman spectroscopy for the determination 0 elements) A group of of monatomic, of molecular structure, particularly since low-boiling gases classified as belonging to the advent of the laser. group 0 of the periodic table and occupy-

232 rate of reaction ing a position between the highly elec- the manufacture of chlorobenzene, and tronegative group 17 elements and the thence phenol, from benzene. Benzene highly electropositive group 1 elements. vapor, hydrogen chloride, and air are They are: helium (He), neon (Ne), argon passed over a copper(II) chloride catalyst (Ar), krypton (Kr), xenon (Xe), and radon (230°C): → (Rn). This complete filling of the s and p 2C6H6 + 2HCl + O2 2C6H5Cl + levels gives a closed-shell structure and is 2H2O associated with a general lack of chemical The conversion to phenol is by a silicon reactivity and very high ionization ener- catalyst (425°C): → gies. It is the acquisition of a stable rare-gas C6H5Cl + H2O HCl + C6H5OH configuration that is associated with determining the valence of many covalent and rate constant (velocity constant; specific ionic compounds. reaction rate) Symbol: k The constant of Prior to 1962 the rare gases were fre- proportionality in the rate expression for a quently called inert gases as no chemical chemical reaction. For example, in a reac- compounds were known (there were a few tion A + B → C, the rate may be propor- clathrates and ‘hydrates’), but the realiza- tional to the concentration of A multiplied tion that the ionization potential of xenon by that of B; i.e. was sufficiently low to be accessible to rate = k[A][B] chemical reaction led to the preparation of where k is the rate constant for this partic- several fluorides, oxides, oxyfluorides, and ular reaction. The constant is independent a hexafluoroplatinate of xenon. Several of the concentrations of the reactants but unstable krypton and radon compounds depends on temperature; consequently the have been synthesized. temperature at which k is recorded must be Argon forms about 1% of the atmos- stated. The units of k vary depending on phere but the other gases are present in the number of terms in the rate expression, only minute traces (excluding radon). They but are easily determined remembering are obtained by fractionation of liquid air that rate has the units s–1. or (in the USA) of natural gas. Consider- able amounts of argon are produced as a rate-determining step (limiting step) by-product from ammonia-plant tail gas. The slowest step in a multistep reaction. Their applications depend heavily on their Many chemical reactions are made up of a inertness; for example, welding (Ar), filling number of steps in which the one with the light bulbs (Ar), gas-stirring in high tem- lowest rate is the one that determines the perature metallurgy (Ar), powder technol- rate of the overall process. ogy (Ar), discharge tubes (Ne), and The overall rate of a reaction cannot chemical research as inert carriers (He, Ar). exceed the rate of the slowest step. For ex- Neon has been proposed as an oxygen dilu- ample, the first step in the reaction between ent for deep-sea diving because of its lower acidified potassium iodide solution and hy- solubility in blood. Liquid helium is exten- drogen peroxide is the rate-determining sively used in low-temperature work and step: – → – radon is used therapeutically as a source of H2O2 + I H2O + OI (slow) α-particles. H+ + OI– → HOI (fast) + – → The gases helium and argon are formed HOI + H + I I2 + H2O (fast) by radioactive decay in various minerals, for example argon by electron capture of rate of reaction A measure of the amount 40K. This mechanism may be applied to of reactant consumed in a chemical reac- age-determination of minerals. Radon is tion in unit time. It is thus a measure of the generally obtained as 222Rn from decay of number of effective collisions between re- radium. The half-life is only about 3.8 actant molecules. The rate at which a reac- days. tion proceeds can be measured by the rate the reactants disappear or by the rate at Rashig process /rash-ig/ A method for which the products are formed. The princi-

233 rationalized units pal factors affecting the rate of reaction are ric acid, etc. – used for experiment and temperature, pressure, concentration of re- analysis. actants, light, and the action of a catalyst. The units usually used to measure the rate realgar /ree-al-ger/ The mineral form of –3 –1 of a reaction are mol dm s . See also law arsenic(II) sulfide, As4S4. It is bright red in of mass action. color and used as a pigment, in tanning, and in pyrotechnics. rationalized units A system of units in which the equations have a logical form re- real gas See gas laws. lated to the shape of the system. SI units form a rationalized system of units. In it rearrangement A reaction in which the formulae concerned with circular symme- groups of a compound rearrange them- try contain a factor of 2π; those concerned selves to form a different compound. with radial symmetry contain a factor of 4π. reciprocal proportions, law of See equivalent proportions, law of. raw material A substance from which other substances are made. In the chemical recrystallization /ree-kris-tă-li-zay-shŏn/ industry it may be simple (such as nitrogen The repeated crystallization of a com- from air used to make ammonia) or compound to ensure purity of the sample. plex (such as coal and petroleum, used to /rek-tă-fÿd/ A constant- make a wide range of products). rectified spirit boiling mixture of ethanol and water that contains about 6% water; no more water rayon /ray-on/ An artificial fiber formed can be removed by further distillation. It is from wood pulp (cellulose). There are two used as an industrial solvent. types. Viscose rayon is made by dissolving the cellulose in carbon disulfide and red lead See dilead(II) lead(IV) oxide. sodium hydroxide. The solution is forced through a fine nozzle into an acid bath, redox /ree-doks/ Relating to the process which regenerates the fibers. Acetate rayon of oxidation and reduction, which are inti- is made by dissolving cellulose acetate in an mately connected in that during oxidation organic solvent, and forcing the solution by chemical agents the oxidizing agent it- through a nozzle. The solvent is evapo- self becomes reduced, and vice versa. Thus rated, and the cellulose acetate thus ob- an oxidation process is always accompa- tained as fibers. nied by a reduction process. In electrochemical processes this is equally true, reactant /ree-ak-tănt/ A compound taking oxidation taking place at the anode and re- part in a chemical reaction. duction at the cathode. These systems are often called redox systems, particularly reaction See chemical reaction. when the interest centers on both compounds. reactive dye A dye that ‘sticks’ to the Oxidizing and reducing power is indi- fibers of a fabric by forming covalent cated quantitatively by the redox potential chemical bonds with the substance of the or standard electrode potential, EŠ. fabric. The dyes used to color the cellulose Redox potentials are normally expressed fibers in rayon are examples of reactive as reduction potentials. They are obtained dyes. by electrochemical measurements and the + values are referred to the H /H2 couple for reagent /ree-ay-jĕnt/ A compound that re- which EŠ is set equal to zero. Thus in- acts with another (the substrate). The term creasingly negative potentials indicate in- is usually used for common laboratory creasing ease of oxidation or difficulty of chemicals – sodium hydroxide, hydrochlo- reduction. Thus in a redox reaction the half

234 relative molecular mass reaction with the most positive value of manufacture of methylbenzene from hep- EŠ is the reduction half and the half reac- tane: → tion with the least value of EŠ (or most C7H16 C6H11CH3 highly negative) becomes the oxidation This first step is the production of methyl half. See also electrode potential. cyclohexane, which then loses six hydrogen atoms to give methylbenzene: → red phosphorus See phosphorus. C6H11CH3 C6H5CH3 + 3H2 See also steam reforming. reducing agent See reduction. refractory /ri-frak-tŏ-ree/ Describing a reduction /ri-duk-shŏn/ The gain of elec- compound (e.g. an inorganic oxide) that trons by such species as atoms, molecules, has a very high melting point. or ions. It often involves the loss of oxygen from a compound, or addition of hydro- Regnault’s method A method used for gen. Reduction can be effected chemically, the determination of the density of gases. A i.e. by the use of reducing agents (electron bulb of known volume is evacuated and donors), or electrically, in which case the weighed then the gas is admitted at a reduction process occurs at the cathode. known pressure (from a vacuum line) and For example, the bulb weighed again. The temperature is 2Fe3+ + Cu → 2Fe2+ + Cu2+ also noted and the data corrected to STP. where Cu is the reducing agent and Fe3+ is The method is readily applicable to the de- reduced, and termination of approximate relative molecular masses of gaseous samples. The 2H O + SO + 2Cu2+ → 2 2 method is named for the French physicist 4H+ + SO 2– + 2Cu+ 4 and chemist Henri Victor Regnault where SO is the reducing agent and Cu2+ 2 (1800–78). is reduced. Tin(II) chloride, sulfur(IV) oxide, the relative atomic mass (r.a.m.) Symbol: hydrogensulfite ion, and hydroxylamine A The ratio of the average mass per atom hydrochloride are common reducing r of the naturally occurring element to 1/12 agents. See also redox. of the mass of an atom of nuclide 12C. It was formerly called atomic weight reduction potential See electrode potential. relative density Symbol: d The ratio of the density of a given substance to the den- refining The process of removing impuri- sity of some reference substance. The rela- ties from a substance or of extracting a tive densities of liquids are usually substance from a mixture. measured with reference to the density of water at 4°C. Relative densities are also refluxing /ri-fluks-ing/ The process of specified for gases; usually with respect to boiling a liquid in a vessel connected to a air at STP. The temperature of the sub- condenser, so that the condensed liquid stance is stated or is understood to be runs back into the vessel. By using a reflux 20°C. Relative density was formerly called condenser, the liquid can be maintained at specific gravity. its boiling point for long periods of time, without loss. The technique is a standard relative molecular mass Symbol: Mr method of carrying out reactions in or- The ratio of the average mass per molecule ganic chemistry. of the naturally occurring form of an element or compound to 1/12 of the mass of reforming The cyclization of straight- an atom of nuclide 12C. This was formerly chain hydrocarbons from crude oil by called molecular weight. It does not have to heating under pressure with a catalyst, usu- be used only for compounds that have dis- ally platinum on alumina. For example, the crete molecules; for ionic compounds (e.g.

235 relaxation

NaCl) and giant-molecular structures (e.g. single and double bonds. The bonding elec- BN) the formula unit is used. trons of the compound have a different distribution in the molecules. The actual relaxation The process by which an ex- bonding in the molecule can be regarded as cited species loses energy and falls to a a hybrid of two or more conventional lower energy level (such as the ground forms of the molecule, called resonance state). forms or canonical forms. The result is a resonance hybrid. For example, the car- rem /rem/ (radiation equivalent man) A bonyl group in a ketone has negative unit for measuring the effects of radiation charge on the oxygen atom. It can be de- dose on the human body. One rem is equiv- scribed as a resonance hybrid, somewhere alent to an average adult male absorbing between =C=O, in which a pair of electrons one rad of radiation. The biological effects is shared between the C and the O, and depend on the type of radiation as well as =C+–O–, in which the electrons are local- the energy deposited per kilogram. ized on the O atom. Note that the two canonical forms do not contribute equally resin /rez-in/ A yellowish insoluble or- in the hybrid. The bonding of benzene can ganic compound exuded by trees as a vis- be represented by a resonance hybrid of cous liquid that gradually hardens on two Kekulé structures and, to a lesser ex- exposure to air to form a brittle amor- tent, three Dewar structures. phous solid. Synthetic resins are artificial polymers used in making adhesives, insula- resonance ionization spectroscopy tors and paints. See also rosin. (RIS) A type of spectroscopy that detects specific types of atoms using lasers. The resolution (of racemates) The separation frequency of the laser is chosen so that only of a racemate into the two optical isomers. the atoms of interest in a sample are ex- This cannot be done by normal methods, cited by the laser. such as crystallization or distillation, because the isomers have identical physical /rez-or-să-nol, -nohl/ See ben- properties. The main methods are: resorcinol 1. Mechanical separation. Certain opti- zene-1,3-diol. cally active compounds form crystals with distinct left- and right-handed retort A piece of laboratory apparatus shapes. The crystals can be sorted by consisting of a glass bulb with a long nar- hand. row neck. In industrial chemistry, various 2. Chemical separation. The mixture is re- metallic vessels in which distillations or reacted with an optical isomer. The prod- actions take place are called retorts. ucts are then not optical isomers of each other, and can be separated by physical retrosynthetic analysis /ret-roh-sin-th’ĕ- means. tik/ A technique for planning the synthesis For instance, a mixture of D- and L- of an organic molecule. The structure of forms of an acid, acting with a pure L-base, the molecule is considered and it is divided produces two salts that can be separated by into imaginary parts, which could combine fractional crystallization and then recon- by known reactions. These disconnections verted into the acids. of the molecule suggest charged fragments, 3. Biochemical separation. Certain organic known as synthons, which give a guide to compounds can be separated by using bac- possible reagents for the synthesis. teria that feed on one form only, leaving the other. reverberatory furnace /ri-ver-bĕ-ră-tor- ee, -toh-ree/ A furnace for smelting metals. resonance (mesomerism) The behavior of It has a curved roof so that heat is reflected many compounds cannot be adequately downwards, the fuel being in one part of explained by a single structure using simple the furnace and the ore in the other.

236 RNA reverse osmosis A process by which sition metal that usually occurs naturally water containing a salt is separated via a with molybdenum (it is extracted from flue semipermeable membrane into pure water dust in molybdenum smelters). The metal and salt water streams by subjecting the in- is chemically similar to manganese and is coming water to pressures significantly used in alloys and catalysts. greater than its OSMOTIC PRESSURE. This Symbol: Re; m.p. 3180°C; b.p. 5630°C; causes pure water to be forced through the r.d. 21.02 (20°C); p.n. 75; r.a.m. 186.207. membrane, leaving the salt behind. Reverse osmosis is used in the purification of sea rheology /ree-ol-ŏ-jee/ The study of the water. See osmosis. ways in which matter can flow. This topic is of particular interest in the study of poly- reversible change A change in the pres- mers. sure, volume, or other properties of a system, in which the system remains at rhodium /roh-dee-ŭm/ A rare silvery hard equilibrium throughout the change. Such transition metal. It is difficult to work and processes could be reversed; i.e. returned to highly resistant to corrosion. Rhodium oc- the original starting position through the curs native but most is obtained from cop- same series of stages. They are never real- per and nickel ores. It is used in protective ized in practice. An isothermal reversible finishes, alloys, and as a catalyst. compression of a gas, for example, would Symbol: Rh; m.p. 1966°C; b.p. 3730°C; have to be carried out infinitely slowly and r.d. 12.41 (20°C); p.n. 45; r.a.m. involve no friction, etc. Ideal energy trans- 102.90550. fer would have to take place between the gas and the surroundings to maintain a rhombic crystal /rom-bik/ See crystal sys- constant temperature. tem. In practice, all real processes are irreversible changes in which there is not an ribonucleic acid /rÿ-boh-new-klee-ik/ See equilibrium throughout the change. In an RNA. irreversible change, the system can still be returned to its original state, but not ribose /rÿ-bohs/ (C5H10O5) A monosac- through the same series of stages. For a charide; a component of RNA. closed system, there is always an entropy increase involved in an irreversible change. ring A closed loop of atoms in a molecule, as in benzene or cyclohexane. A fused ring reversible reaction A chemical reaction is one joined to another ring in such a way that can proceed in either direction. For ex- that they share two atoms. Naphthalene is ample, the reaction: an example of a fused-ring compound. ˆ N2 + 3H2 2NH3 is reversible. In general, there will be an ring closure A reaction in which one part equilibrium mixture of reactants and prod- of an open chain in a molecule reacts with ucts. another part, so that a ring of atoms is formed. RF value A measure of the relative distance traveled by a sample in a chromatography RIS See resonance ionization spec- experiment. It is obtained by dividing the troscopy. distance traveled by the solvent front into the distance traveled by the sample. Under RNA (ribonucleic acid) A nucleic acid standard conditions, the RF value is char- found mainly in the cytoplasm and in- acteristic of a particular substance. See volved in protein synthesis. It is a single paper chromatography; thin-layer chro- polynucleotide chain similar in composi- matography. tion to a single strand of DNA except that the sugar ribose replaces deoxyribose and rhenium /ree-nee-ŭm/ A rare silvery tran- the pyrimidine base uracil replaces

237 rock thymine. RNA is synthesized on DNA in rubber A natural or synthetic polymeric the nucleus and exists in three forms. In elastic material. Natural rubber is a poly- certain viruses, RNA is the genetic mater- mer of methylbuta-1,3-diene (isoprene). ial. Various synthetic rubbers are made by polymerization; for example chloroprene rock A definable part of the Earth’s crust rubber (from 2-chlorobuta-1,3-diene) and made up of a mixture of MINERALS. It may silicone rubbers. See also vulcanization. be hard (for example, granite), soft (chalk), consolidated (clay), or loose (sand). rubidium /roo-bid-ee-ŭm/ A soft silvery highly reactive element of the alkali-metal rock salt (halite) A transparent naturally group. Naturally occurring rubidium com- occurring mineral form of sodium chlo- prises two isotopes, one of which, 87Rb, is ride. radioactive (half-life 5 × 1010 years). It is found in small amounts in several complex roentgen /rent-gĕn/ Symbol: R A unit of silicate minerals, including lepidolite. Ru- radiation, used for x-rays and gamma rays, bidium is used in vacuum tubes, photo- defined in terms of the ionizing effect on cells, and in making special glass. × –4 air. One roentgen induces 2.58 10 Symbol: Rb; m.p. 39.05°C; b.p. 688°C; coulomb of charge in one kilogram of dry r.d. 1.532 (20°C); p.n. 37; r.a.m. 85.4678. air. The unit is named for the German physicist Wilhelm Konrad Roentgen rubidium–strontium dating A tech- (1845–1923). nique for dating rocks. It depends on the radioactive decay of the radioisotope 87Rb roentgenium /rent-gĕn-ee-ŭm/ A radioac- to 87Sr (half-life 4.7 × 1010 years). If the tive element produced synthetically. It is ratio 87Sr/87Rb is measured it is possible to named for Wilhelm Roentgen estimate the age of the rock. See also ra- Symbol: Rg; p.n. 111. dioactive dating. Rose’s metal A fusible alloy containing ruby A gemstone variety of the mineral 50% bismuth, 25–28% lead, and tin. Its corundum (aluminum oxide, Al O ) col- low melting point (about 100°C) leads to 2 3 its use in fire-protection devices. ored red by chromium impurities. Rubies can also be made synthetically. They are rosin A brittle yellow or brown resin that used in jewelry, as bearings in watches, and remains after the distillation of turpentine. in some lasers. It is used as a flux in soldering and in making paints and varnishes. Powdered rosin rusting The corrosion of iron in air to gives a ‘grip’ to violin bows and boxers’ form an oxide. Both oxygen and moisture shoes. See also resin. must be present for rusting to occur. The process is electrolytic, involving electro- rotary dryers Devices commonly used in chemical reactions on the wet iron: 2+ – the chemical industry for the drying, mix- Fe(s) → Fe (aq) + 2e – → – ing, and sintering of solids. They consist es- 2H2O + O2(aq) + 4e 4OH (aq) sentially of a rotating inclined cylinder, Iron(II) hydroxide precipitates and is which is longer in length than in diameter. oxidized to the red hydrated iron(III) oxide Gases flow through the cylinder in either a Fe2O3.H2O. countercurrent or cocurrent direction to regulate the flow of solids, which are fed ruthenium /roo-th’ee-nee-ŭm/ A transi- into the end of the cylinder. Rotary dryers tion metal that occurs naturally with plat- can be applied to both batch and continu- inum. It forms alloys with platinum that ous processes. are used in electrical contacts. Ruthenium is also used in jewelry alloyed with palla- R-S convention See optical activity. dium.

238 Rydberg constant

Symbol: Ru; m.p. 2310°C; b.p. eties of rutile are used as a semiprecious 3900°C; r.d. 12.37 (20°C); p.n. 44; r.a.m. gemstone. 101.07. Rydberg constant /rid-berg/ A constant rutherfordium /ruth-er-for-dee-ŭm/ A ra- that occurs in formula for the frequencies dioactive metal not found naturally on of spectral lines in atomic spectra. For the × earth. It is the first transactinide metal. hydrogen atom it has the value 1.0968 7 –1 Atoms of rutherfordium are produced by 10 m . The value of the Rydberg constant can be calculated from the BOHR THEORY of bombarding 249Cf with 12C or by bom- the hydrogen atom and from quantum me- barding 248Cm with 18O. ° chanics. These calculations showed that: Symbol: Rf; m.p. 2100 C (est.); b.p. R = Μ 2me4c3/8h3 ° 0 5200 C (est.); r.d. 23 (est.); most stable where Μ is the magnetic constant, m and 261 0 isotope Rf (half-life 65s). e are the mass and charge respectively of an electron, h is the Planck constant and c is rutile /roo-teel, -tÿl/ A naturally occurring the speed of light in a vacuum. The con- reddish-brown form of titanium(IV) oxide, stant is named for the Swedish physicist Jo- TiO4. It is an ore of titanium and is also hannes Robert Rydberg (1854–1919). See used in making ceramics. Some clear vari- also hydrogen atom spectrum.

239 S

Sabatier–Senderens process A method preference. In other words, the zinc rod of hydrogenating unsaturated vegetable sacrifices itself for the steel pipeline. The oils to make margarine, using hydrogen same effect occurs with galvanized iron. If and a nickel catalyst. It is named for the the zinc coating is scratched, the iron ex- French chemists Paul Sabatier (1854– posed does not rust until all the zinc has 1941) and Jean-Baptiste Senderens (1856– dissolved away. (Note that tin, being less 1937). See also hardening. electropositive than iron, has the opposite effect.) saccharide /sak-ă-rÿd, -rid/ See sugar. safety lamp (Davy lamp) A type of oil saccharin /sak-ă-rin/ (C7H5NO3S) A lamp for use in coal mines designed so that white crystalline organic compound used it will not ignite any methane (firedamp) as an artificial sweetener; it is about 550 present and cause an explosion. The flame times as sweet as sugar (sucrose). It is is surrounded by a fine metal gauze which nearly insoluble in water and so generally dissipates the heat from the flame but never used in the form of its sodium salt. Possible reaches the ignition temperature of links with cancer in animals has restricted methane. If methane is present it burns in- its use in some countries. side the gauze; the lamp can be used as a test for pockets of methane. The lamp is Sachse reaction /sak-sĕ/ A process for the also named for the British chemist Sir manufacture of ethyne from natural gas Humphry Davy (1778–1829). (methane). Part of the methane is burned in two stages to raise the furnace temperature sal ammoniac /sal ă-moh-nee-ak/ See am- to about 1500°C. Under these conditions, monium chloride. the rest of the methane is converted to ethyne and hydrogen: salicylate /sal-ă-sil-ayt, sal-ă-sil-ayt, să- → 2CH4 C2H2 + 3H2 liss-ă-layt/ (hydroxybenzoate) A salt or The process is important since it provides a ester of salicylic acid. source of ethyne from readily available natural gas, thus avoiding the expensive salicylic acid /sal-ă-sil-ik/ (2-hydroxyben- carbide process. zoic acid; C6H4(OH)COOH) A crystalline aromatic carboxylic acid. It is used in med- sacrificial protection A method of pro- icines, as an antiseptic, and in the manu- tection against electrolytic corrosion (espe- facture of azo dyes. Its ethanoyl (acetyl) cially rusting). In protecting steel pipelines, ester is aspirin. See aspirin; methyl salicy- for instance, zinc or magnesium rods are late. buried in the ground at points along the line and connected to the pipeline. Rusting saline /say-lÿn/ Containing a salt, espe- of iron is an electrochemical process in cially an alkali-metal halide such as sodium which Fe2+ ions dissolve in the water in chloride. contact with the surface. A more electropositive element, such as zinc, protects salt A compound with an acidic and a against this because Zn2+ ions dissolve in basic radical, or a compound formed by

240 sandwich compound total or partial replacement of the hydro- sand A mineral form of silica (silicon(IV) gen in an acid by a metal. In general terms oxide, SiO2) consisting of separate grains a salt is a material that has identifiable of quartz. It results from erosion of quartz- cationic and anionic components. containing rocks; the grains may be rounded by the tumbling action of water or salt bridge An electrical contact between wind. Sand is used in concrete and mortar two half cells, used to prevent mixing. A and in making glass and other ceramics. glass U-tube filled with potassium chloride in agar is often used. Sandmeyer reaction /sand-mÿ-er/ A method of producing chloro- and bromo- saltcake /sawlt-kayk/ An impure form of substituted derivatives of aromatic compounds by using the DIAZONIUM SALT with SODIUM SULFATE, formerly produced indus- a copper halide. The reaction starts with an trially as a by-product of the LEBLANC amine, which is diazotized at low tempera- PROCESS. ture by using hydrochloric acid and sodium nitrite (to produce nitrous acid, salt hydrate A metallic salt in which the HNO2). For example: metal ions are surrounded by a fixed num- → + C6H5NH2 + NaNO2 + HCl C6H5N2 ber of water molecules. The water mol- – – + + Cl + OH + Na + H2O ecules are bound to the metal ions by The copper halide (e.g. CuCl) acts as a cation–dipole interactions. In the solid state alyst to give the substituted benzene deriv- the water molecules form part of the crys- ative: + – → tal structure. It is thus a clathrate. C6H5N2 + Cl C6H5Cl + N2 Salt hydrates that contain several mol- This reaction was discovered by the Ger- ecules of water for each metal ion can lose man chemist Traugott Sandmeyer them progressively (effloresce) if the pres- (1854–1922) in 1884. A variation of the sure of water vapor is kept below the dis- reaction, in which the catalyst is freshly sociation pressure of the system; eventually precipitated copper powder, was reported an anhydrous salt is formed. Alternatively, in 1890 by the German chemist Ludwig if the vapor pressure is continuously raised Gatterman (1860–1920). This is known as the system will add molecules of water the Gatterman reaction (or Gat- (deliquesce) until a saturated solution terman–Sandmeyer reaction). forms. sandstone A sedimentary rock consisting salting out The precipitation of a colloid of consolidated sand grains cemented to- (such as gelatin or soap) by adding an ionic gether with calcium carbonate, clay, or oxides of iron. It is used mainly as a building salt to a solution. See gelatin; soap. stone. saltpeter /sawlt-pee-ter/ See potassium ni- sandwich compound A type of trate. organometallic compound formed between transition metal ions and aromatic com- sal voh-lat-ă-lee sal volatile / / See ammo- pounds, in which the metal ion is ‘sand- nium carbonate. wiched’ between two rings. Four, five, six, seven, and eight-membered rings are samarium /să-mair-ee-ŭm/ A silvery ele- known to form complexes with a number ment of the lanthanoid series of metals. It of elements including V, Cr, Mn, Co, Ni, occurs in association with other lan- and FE. The bonding in such compounds is thanoids. Samarium is used in the metal- not between the metal ion and individual lurgical, glass, and nuclear industries. atoms on the ring; rather it involves bond- Symbol: Sm; m.p. 1077°C; b.p. ing of d electrons of the ion with the pi- 1791°C; r.d. 7.52 (20°C); p.n. 62; r.a.m. electron system of the ring as a whole. 150.36. FERROCENE is the original example, having

241 saponification two parallel cyclopentadienyl rings sand- rated vapor is at the maximum pressure wiching the iron ion. There are a number (the saturated vapor pressure) at a given of related types of compound. Thus, half- temperature. If the temperature of a satu- sandwich compounds (sometimes known rated vapor is lowered, the vapor con- as piano-stool compounds) have only one denses. Under certain circumstances, the ring bound to the central ion, with other substance may stay temporarily in the ligands coordinating in the normal way. vapor phase; i.e. the vapor contains more Bent sandwich compounds have two rings than the equilibrium concentration of the that are not parallel, and the ion is attached substance. The vapor is then said to be su- to other ligands. Multidecker sandwich persaturated. compounds have more than two parallel rings (and more than two coordinating s-block elements The elements of the ions. first two groups of the periodic table; i.e. group 1 (H, Li, Na, K, Rb, Cs, Fr) and saponification /să-pon-ă-fă-kay-shŏn/ group 2 (Be, Mg, Ca, Sr, Ba, Ra). They are The process of hydrolyzing an ester with a so called because their outer shells have the hydroxide. The carboxylic acid forms a electronic configurations ns1 or ns2. The s- salt. For instance, with sodium hydroxide: block excludes those with inner (n – 1)d RCOOR′ + NaOH → NaOOCR + levels occupied (i.e. it excludes transition R′OH elements, which also have s2 and occasion- The saponification of fats, which are esters ally s1 configurations). of 1,2,3-trihydroxypropane with long- chain carboxylic acids, forms soaps. scandium /skan-dee-ŭm/ A lightweight silvery element belonging to the first tran- sapphire A gemstone variety of the min- sition series. It is found in minute amounts eral corundum (aluminum oxide, Al2O3) in over 800 minerals, often associated with colored blue (or other colors) by impuri- lanthanoids. Scandium is used in high-in- ties. Sapphires can also be made syntheti- tensity lights and in electronic devices. cally. Symbol: Sc; m.p. 1541°C; b.p. 2831°C; r.d. 2.989 (0°C); p.n. 21; r.a.m. saturated compound An organic com- 44.955910. pound that does not contain any double or triple bonds in its structure. A saturated scanning tunneling microscope (STM) compound will undergo substitution reac- An instrument that makes use of quantum- tions but not addition reactions since each mechanical tunneling to investigate the atom in the structure will already have surface structure of a sample of material. In formed its maximum possible number of this technique a sharp conducting tip is single bonds. Compare unsaturated com- brought near a surface. This causes elec- pound. trons to tunnel from the surface to the tip, with the probability of this occurring de- saturated solution A solution that con- pending on both the distance between the tains the maximum equilibrium amount of surface and the tip and the electron density solute at a given temperature. A solution is at the surface. The tunneling produces an saturated if it is in equilibrium with its electrical current which is kept constant by solute. If a saturated solution of a solid is moving the tip up or down as it is moved cooled slowly, the solid may stay tem- over the surface. Single atoms can be ob- porarily in solution; i.e. the solution may served using STM. See also atomic force contain more than the equilibrium amount microscope. of solute. Such solutions are said to be supersaturated. scavenger A compound or chemical species that removes a trace component saturated vapor A vapor that is in equi- from a system or that removes a reactive librium with the solid or liquid. A satu- intermediate from a reaction.

242 self-assembly

Schiff’s base /shiffs/ A type of compound secondary cell See accumulator. formed by reacting an aldehyde or ketone (e.g. RCOR) with an aryl amine (e.g. secondary structure See protein. ArNH2). The product, an N-arylimide, which is usually crystalline, has the for- second-order reaction A reaction in mula R2C:NAr. The compound is named which the rate of reaction is proportional for the German chemist Hugo Schiff to the product of the concentrations of two (1834–1915). of the reactants or to the square of the concentration of one of the reactants; i.e. Schiff’s reagent An aqueous solution of rate = k[A][B] magenta dye decolorized by reduction with or 2 sulfur(IV) oxide. It is a test for aldehydes rate =k[A] and ketones. Aliphatic aldehydes restore For example, the hydrolysis by dilute the color quickly; aliphatic ketones and alkali of an ester is a second-order reaction: aromatic aldehydes slowly; aromatic ke- rate = k[ester][alkali] tones give no reaction. The rate constant for a second-order reaction has the units mol–1 dm3 s–1. Unlike a Schotten–Baumann reaction /shot-ĕn first-order reaction, the time for a definite bow-mahn/ A method for the preparation fraction of the reactants to be consumed is of N-phenylbenzamide (benzanilide) in dependent on the original concentrations. which a mixture of phenylamine (aniline) The settling of a suspen- and sodium hydroxide is stirred while ben- sedimentation sion, either under gravity or in a centrifuge. zoyl chloride is added slowly. The N- The speed of sedimentation can be used to phenylbenzamide precipitates and can be estimate the average size of the particles. recrystallized from hot ethanol: This technique is used with an ultracen- C H NH + C H COCl → 6 5 2 6 5 trifuge to find the relative molecular C H NH.COC H + HCl 6 5 6 5 masses of macromolecules. shot-kee Schottky defect / / See defect. seed A small crystal added to a gas or liquid to assist solidification or precipitation scrubber The part of a chemical plant from a solution. The seed, usually a crystal that removes impurities from a gas by pass- of the substance to be formed, enables par- ing it through a liquid. ticles to pack into predetermined positions so that a larger crystal can form. seaborgium /see-bor-gee-ŭm/ A radioactive metallic element not occurring natu- selenium /si-lee-nee-ŭm/ A metalloid ele- rally on Earth. It can be made by ment existing in several allotropic forms 249 18 bombarding Cf with O nuclei using a and belonging to group 16 of the periodic cyclotron. Six isotopes are known. table. It occurs in minute quantities in sul- 266 Symbol: Sg; most stable isotope Sg fide ores and industrial sludges. The com- (half-life 27.3s). mon gray metallic allotrope is very light-sensitive and is used in photocells, second Symbol: s The SI base unit of time. solar cells, some glasses, and in xerogra- It is defined as the duration of phy. The red allotrope is unstable and re- 9 192 631 770 cycles of a particular wave- verts to the gray form under normal length of radiation corresponding to a conditions. transition between two hyperfine levels in Symbol: Se; m.p. 217°C (gray); b.p. the ground state of the cesium-133 atom. 684.9°C (gray); r.d. 4.79 (gray); p.n. 34; r.a.m. 78.96. secondary alcohol See alcohol. self-assembly See supramolecular chem- secondary amine See amine. istry.

243 Seliwanoff’s test

Seliwanoff’s test A test for ketose SUGARS Equilibrium is reached at a semiperme- in solution. The reagent used consists of re- able membrane if the chemical potentials sorcinol dissolved in hydrochloric acid. A on both sides become identical; migration few drops are added to the solution and a of solvent molecules towards the solution red precipitate indicates a ketonic sugar. is an attempt by the system to reach equi- The test is named for the Russian chemist librium. The pressure required to halt this F. F. Seliwanoff. migration is the osmotic pressure. semicarbazide /sem-ee-kar-bă-zÿd/ See semipolar bond /sem-ee-poh-ler/ A coor- semicarbazone. dinate bond. semicarbazone /sem-ee-kar-bă-zohn/ A septivalent /sep-tă-vay-lĕnt, sep-tiv-ă-/ type of organic compound containing the (heptavalent) Having a valence of seven. C:N.NH.CO.NH2 grouping, formed by reaction of an aldehyde or ketone with semi- sequence rule See CIP system. carbazide (H2N.NH.CO.NH2). The compounds are crystalline solids with see-kwes-tray-shŏn sharp melting points, which can be used to sequestration / / The characterize the original aldehyde or ke- formation of a complex with an ion in so- tone. lution, so that the ion does not have its normal activity. Sequestering agents are often semiconductor /sem-ee-kŏn-duk-ter/ A chelating agents, such as edta. crystalline material which conducts only under certain conditions. The conductivity, serine /se-reen, -rin/ See amino acids. unlike in metals, increases with temperature because the highest occupied and low- sesqui- Prefix indicating a 2/3 ratio. A est unoccupied energy levels are very close. sesquioxide, for example, would have the A semiconductor can be formed by intro- formula M2O3. A sesquicarbonate is a ducing small amounts of an impurity to an mixed carbonate and hydrogencarbonate ultrapure material. If these impurities can of the type Na2CO3.NaHCO3.2H2O, withdraw electrons from the occupied en- which contains 2 CO3 units and 3 sodium ergy level, leaving ‘holes’ which permit ions. conduction, the resultant semiconduction is known as p-type. Alternatively, these im- sesquiterpene See terpene. purities may donate electrons which enter the unoccupied energy level, thus forming shell A group of electrons that share the an n-type semiconductor. Semiconductors same principal quantum number. Early are used extensively by the electronics in- work on x-ray emission studies used the dustry in such devices as integrated cir- terms K, L, M, and these are still some- cuits. times used for the first three shells: n = 1 K- shell; n = 2 L-shell; n = 3 M-shell. semipermeable membrane /sen-ee-per- mee-ă-băl/ A membrane that, when sepa- /sh’e-răr-dÿ-zing/ A tech- rating a solution from a pure solvent, sherardizing permits the solvent molecules to pass nique used to obtain corrosion-resistant ar- through it but does not allow the transfer ticles of iron or steel by heating with zinc of solute molecules. Synthetic semiperme- dust in a sealed rotating drum for several ° able membranes are generally supported hours at about 375 C. At this temperature on a porous material, such as unglazed the two metals combine, forming internal porcelain or fine wire screens, and are com- layers of zinc–iron and zinc–steel alloys monly formed of cellulose or related mat- and an external layer of pure zinc. Sher- erials. They are used in osmotic studies, gas ardizing is principally used for small parts, separations, and medical applications. such as springs, washers, nuts, and bolts.

244 silicon short period See period. ing and used as a catalyst support and as a drying agent. The silica gel used in desicca- SI See SI units. tors and in packaging to remove moisture is often colored with a cobalt salt to indi- side chain In an organic compound, an cate whether it is still active (blue = dry; aliphatic group or radical attached to a pink = moist). longer straight CHAIN of atoms in an acyclic compound or to one of the atoms in the silicates /sil-ă-kayts, -kits/ A large number ring of a cyclic compound. of compounds containing metal ions and complex silicon–oxygen compounds. The side reaction A chemical reaction that negative ions in silicates are of the form 4– 6– takes place to a limited extent at the same SiO4 , Si2O7 , etc., and many are poly- time as a main reaction. Thus the main meric, containing SiO4 units linked in long product of a reaction may contain small chains, sheets, or three-dimensional arrays. amounts of other compounds. Aluminosilicates and borosilicates are similar materials containing aluminum or siemens /see-mĕnz/ (mho) Symbol: S The boron atoms in the structure. Many sili- SI unit of electrical conductance, equal to a cates occur naturally in rocks and miner- conductance of one ohm–1. The unit is als. named for the German electrical engineer Ernst Werner von Siemens (1816–92). silicic acid /să-liss-ik/ A colloidal or jelly- like hydrated form of silicon(IV) oxide sievert /see-vert/ Symbol: Sv The SI unit of (SiO2), made by adding an acid (such as hy- dose equivalent. It is the dose equivalent drochloric acid) to a soluble SILICATE. when the absorbed dose produced by ionizing radiation multiplied by certain di- silicide /sil-ă-sÿd/ A compound of silicon mensionless factors is 1 joule per kilogram with a more electropositive element. (1 J kg–1). The dimensionless factors are used to modify the absorbed dose to take silicon /sil-ă-kŏn/ A hard brittle gray met- account of the fact that different types of alloid element; the second element in group radiation cause different biological effects. 14 of the periodic table. It has the elec- The unit is named for the Swedish physicist tronic configuration of neon with four ad- Rolf Sievert (1898–1966). ditional outer electrons; i.e., [Ne]3s23p2. Silicon accounts for 27.7% of the mass sigma orbital See orbital. of the Earth’s crust and occurs in a wide variety of silicates with other metals, clays, sigmatropic rearrangement /sig-mă- micas, and sand, which is largely SiO2. The trop-ik/ See pericyclic reaction. element is obtained on a small scale by the reduction of silicon(IV) oxide (SiO2) by silane /sil-ayn/ Any of a small number of carbon or calcium carbide. For semicon- hydrides of silicon: SiH4, Si2H6, Si3H8, etc. ductor applications very pure silicon is Silanes can be made by the action of acids produced by direct reaction of silicon with on magnesium silicide (Mg2Si). They are an HCl/Cl2 mixture to give silicon tetra- unstable compounds and ignite sponta- chloride (SiCl4), which can be purified by neously in air. Only the first few members distillation. This is then decomposed on a of the series are known and there is not the hot wire in an atmosphere of hydrogen. range of ‘hydrosilicon’ compounds to com- For ultra-pure samples zone refining is pare with the hydrocarbons. used. Unlike carbon, silicon does not form allotropes but has only the diamond type silica /sil-ă-kă/ See silicon(IV) oxide. of structure. Silicon does not react with hydrogen silica gel A gel made by coagulating except under extreme conditions in the sodium silicate sol. The gel is dried by heat- presence of chlorine, in which case com-

245 silicon carbide pounds such as trichlorosilane (HSiCl3) are silicon(IV) chloride (silicon tetrachlo- obtained. The hydride SiH4 itself may be ride; SiCl4) A colorless fuming liquid prepared in the laboratory by hydrolysis of which rapidly hydrolyzes in moist air or magnesium silicide (a number of other hy- water. It is used to produce pure silica for drides up to Si6H14 are obtained), or more making special kinds of glass. conveniently by reduction of silicon tetrachloride with lithium tetrahydridoalumi- silicon dioxide /dÿ-oks-ÿd, -id/ See sili- nate: con(IV) oxide. → SiCl4 + LiAlH4 SiH4 + LiCl + AlCl3 The silanes are mildly explosive and the silicones /sil-ă-kohnz/ Polymeric synthetic chloroalkyl silanes extremely so. silicon compounds containing chains of al- Silicon combines with oxygen when ternating silicon and oxygen atoms, with heated in air to form silicon(IV) oxide. The organic groups bound to the silicon atoms. mineral silicates constitute a vast collection Silicones are used as lubricants and water of materials with a wide range of structures repellants and in waxes and varnishes. Sil- including chains, rings, lattices, twisted icone rubbers are superior to natural rub- chains, sheets, and varyingly cross-linked bers in their resistance to both high and structures all based on different assemblies low temperatures and chemicals. See also 2– siloxanes. of [SiO4] tetrahedra. Being a metalloid, silicon is somewhat amphoteric and consequently silica is weakly acidic, dissolving in silicon(IV) oxide (silicon dioxide; silica; fused alkalis to form the appropriate sili- SiO2) A hard crystalline compound occurring naturally in three crystalline forms cate. (quartz, tridymite, and crystobalite). Sand Silicon also forms an immense number is mostly silicon(IV) oxide. Fused silica is a of organic derivatives. In many cases where glassy substance used in laboratory appa- single bonding only is involved these com- ratus. Silica is used in the manufacture of pounds are rather similar to organic glass. analogs with the general distinction that nucleophilic attachment occurs at silicon silicon tetrachloride /tet-ră-klor-ÿd, -id, - (rather than at hydrogen) and bond angles kloh-rÿd, -rid/ See silicon(IV) chloride. at oxygen and nitrogen are often larger than the organic materials. Optical activity siloxanes /să-loks-aynz/ Compounds con- and inversion of activity is observed. The taining Si–O–Si groups with organic major differences are due to the type of groups bound to the silicon atoms. The sil- π π ‘double bond’ available to carbon (p –p ), icones are polymers of siloxanes. and to silicon (p → dπ or back bonding). Thus silicon does not form conventional silver A transition metal that occurs na- double bonds and silicon bonds to oxygen tive and as the sulfide (Ag2S) and chloride are of the ether type (as in siloxanes) rather (AgCl). It is extracted as a by-product in re- than the ketone type. The Si–OH bond is fining copper and lead ores. Silver darkens also very much less stable than the alcohol in air due to the formation of silver sulfide. link, R–OH, ready condensation to the It is used in coinage alloys, tableware, and siloxane occurring in the silicon case: jewelry. Silver compounds are used in pho- → 2R3SiOH R3Si–O–SiR3 + H2O tography. Symbol: Si; m.p. 1410°C; b.p. 2355°C; Symbol: Ag; m.p. 961.93°C; b.p. r.d. 2.329 (20°C); p.n. 14; r.a.m. 28.0855 2212°C; r.d. 10.5 (20°C); p.n. 47; r.a.m. 107.8682. silicon carbide (carborundum; SiC) A black very hard crystalline solid made by silver(I) bromide (AgBr) A pale yellow heating silicon(IV) oxide (sand) with car- precipitate obtained by adding a soluble bon (coke) in an electric furnace. It is used bromide solution to a solution of silver(I) as an abrasive. nitrate. The halide dissolves in concen-

246 SI units trated ammonia solution but not in dilute the photographic industry. In the labora- ammonia solution. It is used extensively in tory, it is used both as an analytical and photography for making the light-sensitive volumetric reagent. Silver(I) nitrate in solu- emulsions for plates and films. Silver(I) tion and in the solid state can oxidize or- bromide crystallizes in a similar manner to ganic compounds, e.g. aldehydes can be sodium(I) chloride. Unlike silver(I) chlo- oxidized to carboxylic acids; the silver ions ride and silver(I) iodide, silver(I) bromide are reduced to silver. does not absorb ammonia gas. silver(I) oxide (argentous oxide; Ag2O) A silver(I) chloride (AgCl) A compound brown amorphous solid formed by the ad- prepared as a curdy white precipitate by dition of sodium or potassium hydroxide the addition of a soluble chloride solution solution to a solution of silver nitrate. Sil- to a solution of silver(I) nitrate. It occurs in ver(I) oxide turns moist red litmus blue and nature as the mineral ‘horn silver’. Silver(I) decomposes (at 160°C) to give silver and chloride is insoluble in water but dissolves oxygen. Silver(I) oxide dissolves in concen- in concentrated hydrochloric acid and con- trated ammonia solution, forming the + centrated ammonia solution. It is rather complex ion [Ag(NH3)2] . In organic unreactive but is affected by sunlight, being chemistry it is used when moist to convert used extensively in photography. Silver(I) alkyl halides to the corresponding alcohol chloride crystallizes in the sodium chloride and when dry to convert alkyl halides into lattice pattern. It absorbs ammonia gas ethers. forming ammines, e.g. AgCl.2NH3 and AgCl.3NH3. silver(II) oxide (argentic oxide; AgO) A black diamagnetic substance prepared by silver(I) iodide (AgI) A pale yellow pre- the oxidation of either silver or silver(I) cipitate prepared by the addition of a solu- oxide using ozone. Alternatively it can be ble iodide solution to a solution of silver(I) prepared as a precipitate by the addition of nitrate. Silver(I) iodide occurs in nature as a solution of potassium persulfate to one of iodoargyrite in the form of hexagonal crys- silver(I) nitrate. tals. It is virtually insoluble in ammonia solution and is used in the photographic single bond A covalent bond between industry. Silver(I) iodide will absorb am- two elements that involves one pair of elec- monia gas. It is trimorphic and is found to trons only. It is represented by a single line, contract when heated and expand on cool- for example H–Br, and is usually a sigma ing. bond, although it can be a pi bond. Com- pare multiple bond. See also orbital. silver-mirror test A test for the aldehyde group. A few drops of the sample are sintering /sin-ter-ing/ A process in which warmed with TOLLEN’S REAGENT. An alde- certain powdered substances (e.g. metals, hyde reduces Ag+ to silver metal, causing a ceramics) coagulate into a single mass brilliant silver mirror to coat the inside when heated to a temperature below the wall of the tube. substance’s melting point. Sintered glass is a porous material used for laboratory fil- silver(I) nitrate (AgNO3) A white crys- tration. talline solid prepared by dissolving silver in dilute nitric acid and crystallizing the solu- SI units (Système International d’Unités) tion. Silver(I) nitrate is dimorphous, crys- The internationally adopted system of tallizing in the orthorhombic and units used for scientific purposes. It has hexagonal systems. It undergoes thermal seven base units and two dimensionless decomposition to yield silver, nitrogen(IV) units, formerly called supplementary units. oxide, and oxygen. Probably the most im- Derived units are formed by multiplication portant silver salt, it is used in the medical and/or division of base units. Standard pre- industry for the treatment of warts and in fixes are used for multiples and submulti-

247 SI units

BASE AND DIMENSIONLESS SI UNITS

Physical quantity Name of SI unit Symbol for SI unit length meter m mass kilogram(me) kg time second s electric current ampere A thermodynamic temperature kelvin K luminous intensity candela cd amount of substance mole mol *plane angle radian rad *solid angle steradian sr *supplementary units

DERIVED SI UNITS WITH SPECIAL NAMES

Physical quantity Name of SI unit Symbol for SI unit frequency hertz Hz energy joule J force newton N power watt W pressure pascal Pa electric charge coulomb C electric potential difference volt V electric resistance ohm Ω electric conductance siemens S electric capacitance farad F magnetic flux weber Wb inductance henry H magnetic flux density tesla T luminous flux lumen lm illuminance (illumination) lux lx absorbed dose gray Gy activity becquerel Bq dose equivalent sievert Sv

DECIMAL MULTIPLES AND SUBMULTIPLES USED WITH SI UNITS

Submultiple Prefix Symbol Multiple Prefix Symbol 10–1 deci- d 101 deca- da 10–2 centi- c 102 hecto- h 10–3 milli- m 103 kilo- k 10–6 micro- µ 106 mega- M 10–9 nano- n 109 giga- G 10–12 pico- p 1012 tera- T 10–15 femto- f 1015 peta- P 10–18 atto- a 1018 exa- E 10–21 zepto- z 1021 zetta- Z 10–24 yocto- y 1024 yotta- Y

248 soda water ples of SI units. The SI system is a coherent SN2 reaction See nucleophilic substitu- rationalized system of units. tion. slag Glasslike compounds of compara- soap One of a number of sodium or potas- tively low melting point formed during the sium compounds of fatty acids that are extraction of metals when the impurities in commonly used to improve the cleansing an ore react with a flux. The fact that the properties of water. Soap was the earliest slag is a liquid of comparatively low den- known DETERGENT. It is made by first re- sity means that it can be separated from the acting vegetable oils and animal fats with a liquid metal on which it floats. In a blast strong solution of sodium or potassium hy- furnace, the flux used is limestone droxide to produce organic acids, such as (CaCO3) and the main impurity is silica octadecanoic acid. The soap is then precip- (SiO2). The slag formed is mainly calcium itated out as the salt, e.g. sodium octade- silicate: canoate, by adding excess sodium chloride. → CaCO3 + SiO2 CaSiO3 In water, soap molecules break up to pro- It is used as railroad ballast and in fertiliz- duce ions, which are responsible for the ers and concrete. cleansing properties. slaked lime See calcium hydroxide. soapstone (steatite) A soft type of talc which has a greasy feel and which is easy to slaking See calcium hydroxide. carve to make ornaments. See talc. slip planes The planes of weakness in a soda See sodium carbonate; sodium hy- crystal, e.g. the boundaries between the oc- droxide. tahedral layers in graphite. soda ash See sodium carbonate. slurry A thin paste of suspended solid particles in a liquid. soda glass See glass. smectic crystal /smek-tik/ See liquid crys- soda lime A gray solid produced by tal. adding sodium hydroxide solution to cal- smelting An industrial process for ex- cium oxide, to give a mixture of Ca(OH)2 tracting metals from their ores at high tem- and NaOH. It is used in the laboratory as peratures. Generally the ore is reduced a drying agent and as an absorbent for with carbon (for zinc and tin) or carbon dioxide. monoxide (for iron). Copper and lead are obtained by reduction of the oxide with the sodamide /soh-dă-mÿd/ (NaNH2) A sulfide; for example: white ionic solid formed by passing dry → ammonia over sodium at 300–400°C. The 2Cu2O + Cu2S 6Cu + SO2 A flux is also used to combine with impu- compound reacts with water to give rities and form a slag on top of the molten sodium hydroxide and ammonia. It reacts metal (see slag). with red-hot carbon to form sodium cyanide and with nitrogen(I) oxide to form smithsonite /smith-sŏ-nÿt/ See calamine. sodium azide. Sodamide is used in the Castner process and in the explosives in- SNG Substitute (or synthetic) natural gas. dustry. A mixture of hydrocarbons manufactured from coal or the naphtha fraction of petro- soda water A solution of carbon dioxide leum for use as a fuel. dissolved in water under pressure, used in fizzy drinks. When the pressure is released, SN1 reaction See nucleophilic substitu- the liquid effervesces with bubbles of car- tion. bon dioxide gas. See also carbonic acid.

249 sodium sodium /soh-dee-ŭm/ A soft reactive to a hot concentrated solution of sodium metal; the second member of the alkali hydroxide. Once the reaction has been ini- metals (group 1 of the periodic table). It tiated, sufficient heat is liberated to keep has the electronic configuration of a neon the reaction going; hydrogen is also pro- structure plus one additional outer 3s elec- duced. In solution the aluminate ions have – tron. Electronic excitation in flames or the the structure Al(OH)4 and NaAl(OH)4 is familiar sodium lamps gives a distinctive known as sodium(I) tetrahydroxoalumi- yellow color arising from intense emission nate(III). Addition of sodium hydroxide to at the so called ‘sodium-D’ line pair. The an aluminum salt solution produces a ionization potential is rather low and the white gelatinous precipitate of aluminum sodium atom readily loses its electron (i.e. hydroxide, which dissolves in excess alkali the metal is strongly reducing). The chem- to give a solution of sodium(I) tetrahy- istry of sodium is largely the chemistry of droxoaluminate(III). the monovalent Na+ ion. Sodium occurs widely as NaCl in sea- sodium azide (NaN3) A white solid pre- water and as deposits of halite in dried up pared by passing nitrogen(I) oxide over lakes etc. (2.6% of the lithosphere). The el- heated sodamide. On heating, sodium ement is obtained commercially by elec- azide decomposes to give sodium and ni- trolysis of NaCl melts in which the melting trogen. It is used as a reagent in organic point is reduced by the addition of calcium chemistry and in the preparation of lead chloride; sodium is produced at the iron azide (for use in detonators). cathode (the Downs cell). The metal is extremely reactive. It reacts vigorously with sodium benzenecarboxylate /ben-zeen- the halogens, and also with water to give kar-boks-ă-layt/ (sodium benzoate; hydrogen and sodium hydroxide. The C6H5COONa) A white crystalline powder chemistry of sodium is very similar to that made by neutralizing benzoic acid with of the other members of group 1. sodium hydroxide solution and then evap- Nearly all sodium compounds are solu- orating the solution. It is used as an urinary ble in water. Sodium hydroxide is pro- antiseptic, in the dyeing industry, and as a duced commercially by the electrolysis of food preservative. brine using diaphragm cells or mercury- cathode cells; chlorine is a coproduct. sodium benzoate /ben-zoh-ayt/ See Solutions of sodium metal in liquid am- sodium benzenecarboxylate. monia are blue and have high electrical conductivities; the main current carrier of sodium bicarbonate See sodium hydro- such solutions is the solvated electron. gencarbonate. Such solutions are used in both organic and inorganic chemistry as efficient reducing sodium bisulfate See sodium hydrogen- agents. Sodium also forms a number of sulfate. alkyl and aryl derivatives by reaction with the appropriate mercury compound, e.g.: sodium bisulfite See sodium hydrogen- → (CH3)2Hg + 2Na 2CH3Na + Na/Hg sulfite. These materials are used as catalysts for polymerization reactions. The metal itself sodium borate /bor-ayt, boh-rayt/ See dis- has a body-centered structure. odium tetraborate decahydrate. Symbol: Na; m.p. 97.81°C; b.p. 883°C; r.d. 0.971 (20°C); p.n. 11; r.a.m. sodium bromide (NaBr) A white solid 22.989768. formed by the action of bromine on hot sodium hydroxide solution. Alternatively, sodium acetate See sodium ethanoate. it can be made by the action of dilute hydrobromic acid on sodium carbonate or sodium aluminate (NaAlO2) A white hydroxide. Sodium bromide is soluble in solid produced by adding excess aluminum water and forms crystals similar in shape to

250 sodium dichromate(VI) sodium chloride. It is used in medicine and photography. Sodium bromide forms a hydrate, NaBr.2H2O. sodium carbonate (soda ash; Na2CO3) A white amorphous powder, which aggre- gates on exposure to air owing to the formation of hydrates. Industrially it is prepared by the ammonia–soda (Solvay) process. On crystallizing from aqueous solution large translucent crystals of the decahydrate (Na2CO3.10H2O) are formed (washing soda). These effloresce forming the monohydrate, Na2CO3.H2O. Large quantities of sodium carbonate are used in the manufacture of sodium hydroxide. Washing soda is used as a domestic chloride ion cleanser. The salt produces an alkaline so- sodium ion lution in water by hydrolysis: → Na2CO3 + 2H2O 2NaOH + H2CO3 Sodium-chloride structure It is used in volumetric analysis to stan- dardize strong acids. with chloride ions situated at the middle of each edge and in the center of the cube. sodium chlorate(V) (NaClO3) A white Electrostatic attraction holds the oppo- solid formed by the action of chlorine on sitely charged ions together. hot concentrated sodium hydroxide solu- The lattice can also be thought of as tion, or by the electrolysis of a concen- two interpenetrating face-centered cubes, trated sodium chloride solution. It is one composed of sodium ions and the soluble in water. Sodium chlorate is a pow- other of chloride ions. Other compounds erful oxidizing agent. If heated it yields (e.g. sodium bromide and potassium chlo- oxygen and sodium chloride. The chlorate ride) having their ions arranged in the same is used in explosives, in matches, as a weed positions, are also described as having the killer, and in the textile industry. sodium-chloride structure. sodium chloride (common salt; salt; sodium cyanide (NaCN) A white solid NaCl) A white solid prepared by the neu- formed either by the action of carbon on tralization of hydrochloric acid with aque- sodamide at high temperature or by pass- ous sodium hydroxide. It occurs in sea ing ammonia over sodium at 300–400°C water and natural brines. Natural solid de- to form sodamide and reacting it with car- posits of rock salt are also found in certain bon. The industrial salt is prepared by the places. The compound dissolves in water Castner process and purified by recrystal- with the absorption of heat, its solubility lization from liquid ammonia. It is exchanging very little with temperature. It is tremely poisonous and used as a source of used to season and preserve food. Industri- cyanide and hydrocyanic acid. In the ally, it is used as a raw material in the man- cyanide process it is used in the extraction ufacture of sodium carbonate (Solvay of silver and gold. Its aqueous solutions are process), sodium hydroxide (electrolysis), alkaline due to salt hydrolysis. and soap. Sodium chloride is almost insoluble in alcohol. sodium dichromate(VI) (Na2Cr2O7) An orange deliquescent solid that is very solu- sodium-chloride structure A form of ble in water. It is made from finely pow- crystal structure that consists of a face-cen- dered chromite, which is heated with tered cubic arrangement of sodium ions calcium oxide and sodium carbonate in a

251 sodium dihydrogen phosphate(V) furnace. If an alkali is added to a solution roaluminate is used as a flux in the manu- of the dichromate, the chromate is pro- facture of aluminum. It crystallizes in the duced. At high temperatures, sodium monoclinic system but in forms that closely dichromate decomposes to give the chro- resemble cubes and isometric octahedrals. mate, chromic oxide, and oxygen. It is used as an oxidizing agent, particularly in or- sodium hydride (NaH) A white crys- ganic chemistry and in volumetric analysis talline solid prepared by passing a pure to estimate iron(II) ions and iodide ions. stream of dry hydrogen over sodium at 350°C; the sodium is usually suspended in sodium dihydrogen phosphate(V) /dÿ- an inert medium. Electrolysis of fused hÿ-drŏ-jĕn/ (sodium dihydrogen or- sodium hydride yields hydrogen at the – thophosphate; NaH2PO4) A white solid anode, suggesting the presence of the H prepared by titrating phosphoric acid with ion. Sodium hydride reacts with water to sodium hydroxide solution using methyl form sodium hydroxide solution and hy- orange as the indicator. On evaporation drogen. It is used as a powerful reducing white crystals of the monohydrate are agent to convert water to hydrogen, con- formed. It is used in some baking powders. centrated sulfuric acid to hydrogen sulfide, The monohydrate crystallizes in the or- and iron(III) oxide to iron. Sodium hydride thorhombic system. bursts into flames spontaneously on contact with the halogens at room tempera- sodium dioxide /dÿ-oks-ÿd, -id/ See ture. It dissolves in liquid ammonia to give sodium superoxide. sodamide, NaNH2. sodium ethanoate /eth-ă-noh-ayt/ sodium hydrogencarbonate (sodium bi- (sodium acetate; CH3COONa) A white carbonate; baking soda; NaHCO3) A solid prepared by the neutralization of white solid formed either by passing an ex- ethanoic acid with either sodium carbonate cess of carbon dioxide through sodium car- or sodium hydroxide. Sodium ethanoate bonate or hydroxide solution, or by reacts with sulfuric acid to form sodium precipitation when cold concentrated solu- hydrogensulfate and ethanoic acid; with tions of sodium chloride and ammonium sodium hydroxide it gives rise to sodium hydrogencarbonate are mixed. Sodium hy- carbonate and methane. Sodium ethanoate drogencarbonate decomposes on heating is used in the dyeing industry. to give sodium carbonate, carbon dioxide, and water. With dilute acids, it yields car- sodium fluoride (NaF) A white solid bon dioxide. It is used as a constituent of formed by the action of hydrofluoric acid baking powder, in effervescent beverages, on sodium carbonate or sodium hydroxide and in fire extinguishers. Its aqueous solu- (the reaction between metallic sodium and tions are alkaline as a result of salt hydrol- fluorine is too violent). Sodium fluoride is ysis. Sodium hydrogencarbonate forms soluble in water and reacts with concen- monoclinic crystals. trated sulfuric acid to yield hydrogen fluoride. It is used as a constituent of ceramic sodium hydrogensulfate /hÿ-drŏ-jĕn-sul- enamels, as an antiseptic, and as an agent fayt/ (sodium bisulfate; NaHSO4) A white to prevent fermentation. solid formed either by the partial neutralization of sodium hydroxide solution with sodium formate See sodium methanoate. sulfuric acid, by the action of concentrated sulfuric acid on sodium nitrate, or by heat- sodium hexafluoroaluminate /heks-ă- ing equimolar quantities of sodium chlo- floo-ŏ-roh-ă-loo-mă-nayt/ (cryolite; ride and concentrated sulfuric acid. In Na3AlF6) A compound found in large aqueous solution sodium hydrogensulfate quantities in South Greenland. It is white is strongly acidic. It crystallizes as the or colorless, but may be reddish or brown monohydrate (NaHSO4.H2O), which de- because of impurities. Sodium hexafluo- hydrates on warming. If heated strongly

252 sodium peroxide the pyrosulfate (Na2S2O7) is formed, solid produced by reacting carbon monox- which decomposes to give the sulfate and ide with solid sodium hydroxide at 200°C sulfur(VI) oxide. Sodium hydrogensulfate and 10 atmospheres pressure. Alternatively is used as a cheap source of sulfuric acid it can be prepared by the neutralization of and in the dyeing industry. methanoic acid with sodium hydroxide solution. sodium hydrogensulfite /hÿ-drŏ-jĕn-sul- fÿt/ (sodium bisulfite; NaHSO3) A white sodium monoxide /mon-oks-ÿd, -id/ powder prepared by saturating a solution (Na2O) A white solid formed by burning of sodium carbonate with sulfur(IV) oxide. sodium in a deficiency of oxygen or alter- It is isolated from the aqueous solution by natively by reducing sodium peroxide or precipitation with alcohol. If heated it un- sodium hydroxide with the requisite dergoes thermal decomposition to give amount of sodium. It reacts violently with sodium sulfate, sulfur(VI) oxide, and sul- water to form sodium hydroxide and with fur. Sodium hydrogensulfite is used to ster- acids to form solutions of their salts. ilize wine casks and in medicine as an Sodium monoxide forms cubic crystals. It antiseptic. dissolves in liquid ammonia to give a mixture of sodamide and sodium hydroxide. sodium hydroxide (caustic soda; NaOH) A white deliquescent slightly translucent sodium nitrate (Chile saltpeter; NaNO3) solid. In solution it is a strong alkali and A white solid formed by the neutralization electrolyte. In the laboratory it can be pre- of nitric acid with either sodium carbonate pared by reacting sodium, sodium monox- or sodium hydroxide. It occurs naturally in ide, or sodium peroxide with water. large quantities in South America. Impure Industrially it can be prepared by the elec- industrial sodium nitrate is called caliche. trolysis of sodium chloride using a mercury Sodium nitrate is very soluble in water and cathode (Castner–Kellner) or diaphragm on crystallization forms colorless deliques- cell. It can also be manufactured by the cent crystals. On heating it decomposes to Gossage process. Sodium hydroxide dis- give sodium nitrite and oxygen. When solves readily in water with the evolution heated with concentrated sulfuric acid, ni- of heat. Its solutions have a soapy feel and tric acid is produced. Sodium nitrate is are very corrosive. It is used to absorb used as a fertilizer and as a source of ni- acidic gases, such as carbon dioxide and trates and nitric acid. The salt crystallizes sulfur(IV) oxide. Industrially it is used in in the rhombohedral system and is isomor- soap and paper manufacture and in the pu- phous with the iodate. rification of bauxite. sodium nitrite (NaNO2) A yellowish- sodium iodide (NaI) A white solid white solid formed by the thermal decom- formed by reacting sodium carbonate or position of sodium nitrate. It is readily sodium hydroxide with hydroiodic acid; soluble in water. The anhydrous salt forms the solution is then evaporated. Sodium io- orthorhombic crystals. When treated with dide forms colorless crystals having a cubic cold dilute hydrochloric acid, sodium ni- shape. It is used as a source of iodine and trite forms nitrous acid. It is used in or- in medicine and photography. Acidified so- ganic chemistry in the process of lutions of sodium iodide exhibit reducing diazotization and industrially as a corro- properties owing to the formation of hy- sion inhibitor. droiodic acid. sodium orthophosphate /or-thoh-fos- sodium metasilicate /met-ă-sil-ă-kayt/ fayt/ See trisodium phosphate(V). See sodium silicate. sodium peroxide (Na2O2) A yellowish- sodium methanoate /meth-ă-noh-ayt/ white ionic solid formed by the direct com- (sodium formate; HCOONa) A white bination of burning sodium with excess

253 sodium silicate oxygen. It reacts with water to form bonate or sodium hydroxide. It is readily sodium hydroxide and hydrogen peroxide; soluble in water and crystallizes as color- the latter decomposes rapidly in the alka- less crystals of the heptahydrate line solution to give oxygen. Sodium per- (Na2SO3.7H2O). When treated with dilute oxide is used as a bleaching agent and an mineral acids, sulfur(IV) oxide is evolved. oxidizing agent for such materials as wool At high temperatures, sodium sulfite un- and wood pulp. Sodium peroxide can con- dergoes thermal decomposition to give vert nitrogen(II) oxide to sodium nitrate sodium sulfate and sodium sulfide. and iodine to sodium iodate. sodium superoxide (sodium dioxide; sodium silicate (sodium metasilicate; NaO2) A pale yellow solid obtained by Na2SiO3.5H2O) A colorless crystalline heating sodium peroxide in oxygen at solid used in detergents and other cleaning 490°C. It reacts with water to give hydro- compounds, in refractories, and in cements gen peroxide, sodium hydroxide solution, for ceramics. A concentrated aqueous solu- and oxygen. Commercial sodium peroxide tion is known as water glass and is used as contains 10% sodium superoxide. a sizing agent and for making precipated silica and silica gel. sodium thiosulfate(IV) (Na2S2O3) A white solid prepared either by boiling sodium sulfate (Na2SO4) A white soluble sodium sulfite with flowers of sulfur or by solid formed by heating a mixture of passing sulfur(IV) oxide into a suspension sodium chloride and concentrated sulfuric of sulfur in boiling sodium hydroxide. acid. Industrially it is prepared by the first Sodium thiosulfate is readily soluble in stage of the Leblanc process. Sodium sul- water and crystallizes as large colorless fate forms two hydrates, the decahydrate crystals of the pentahydrate (Na2SO4.10H2O) and the heptahydrate (Na2S2O3.5H2O). It reacts with dilute (Na2SO4.7H2O). Sodium decahydrate, acids to give sulfur and sulfur(IV) oxide. It known as Glauber’s salt, is used in the is used in photography as ‘hypo’ and in- manufacture of glass and as a purgative in dustrially as an antichlor. In volumetric medicine. It effloresces on exposure to air analysis, solutions of sodium thiosulfate to form the anhydrous salt, which is used are usually prepared from the pentahy- as a drying agent in organic chemistry. At drate. On heating it disproportionates to room temperature sodium sulfate crystal- give sodium sulfate and sodium sulfide. lizes in the orthorhombic system; around 250°C there is a transition to the hexago- soft iron Iron that has a low carbon con- nal system. The decahydrate crystallizes in tent and is unable to form permanent mag- the monoclinic form. Glauber’s salt is nets. named for the German chemist Johann Rudolf Glauber (1604–68). soft soap A liquid soap made by saponification with potassium hydroxide (rather sodium sulfide (Na2S) A yellow-red solid than sodium hydroxide). formed by the reduction of sodium sulfate using carbon (or carbon monoxide or hy- soft water See hardness (of water). drogen) at a high temperature. It is a corrosive material and deliquesces to release sol A COLLOID consisting of solid particles hydrogen sulfide. Sodium sulfide forms hy- distributed in a liquid medium. A wide va- ½ drates containing 4 , 5, and 9 H2O. In riety of sols are known; the colors often de- aqueous solution it is readily hydrolyzed, pend markedly on the particle size. The the solution being strongly alkaline. term aerosol is used for solid or liquid phases dispersed in a gaseous medium. sodium sulfite (Na2SO3) A white solid formed by reacting the exact amount of solder /sod-er/ An alloy used in joining sulfur(IV) oxide with either sodium car- metals. The molten solder wets the surfaces

254 Solvay process to be joined, without melting them, and so- The concentration of undissolved solid lidifies on cooling to form a hard joint. The [AB] is also constant, so + – surfaces must be clean and free of oxide Ks = [A ][B ] and a flux is often used to achieve this. Soft Ks is the solubility product of the salt (at a solders consist of lead with up to 60% tin given temperature). For a salt A2B3, for in- and melt in the range 183–250°C. Soft-sol- stance: + 2 – 3 dering is used, for example, in plumbing Ks = [A ] [B ] , etc. and making electrical contacts. Brazing Solubility products are meaningful only for solders are copper–zinc alloys that have sparingly soluble salts. If the product of higher melting points and produce stronger ions exceeds the solubility product, precip- joints than soft solders; silver can be added itation occurs. to produce silver solders. solute /sol-yoot, soh-loot/ A material that solid The state of matter in which the paris dissolved in a solvent to form a solution. ticles occupy fixed positions, giving the substance a definite shape. The particles solution A liquid system of two or more are held in these positions by bonds. Three species that are intimately dispersed within kinds of attraction fix the positions of the each other at a molecular level. The system particles: ionic, covalent, and intermolecu- is therefore totally homogeneous. The lar. Since these bonds act over short dis- major component is called the solvent tances the particles in solids are packed (generally liquid in the pure state) and the closely together. The strengths of these minor component is called the solute (gas, liquid, or solid). three types of bonds are different and so, The process occurs because of a direct therefore, are the mechanical properties of intermolecular interaction of the solvent different solids. with the ions or molecules of the solute. This interaction is called solvation. Part of solid solution A solid composed of two the energy of this interaction appears as a or more substances mixed together at the change in temperature on dissolution. See molecular level. Atoms, ions, or molecules also solid solution; solubility. of one component in the crystal are at lattice positions normally occupied by the solvation /sol-vay-shŏn/ The attraction of other component. Certain alloys are solid a solute species (e.g. an ion) for molecules solutions of one metal in another. Isomor- of solvent. In water, for example, a positive phic salts can also sometimes form solid so- ion will be surrounded by water molecules, lutions, as in the case of crystalline alums. which tend to associate around the ion because of attraction between the positive solubility /sol-yŭ-bil-ă-tee/ The amount of charge of the ion, and the negative part of one substance that could dissolve in an- the polar water molecule. The energy of other to form a saturated solution under this solvation (hydration in the case of specified conditions of temperature and water) is the ‘force’ needed to overcome the pressure. Solubilities are stated as moles of attraction between positive and negative solute per 100 grams of solvent, or as mass ions when an ionic solid dissolves. The at- of solute per unit volume of solvent. traction of the dissolved ion for solvent molecules may extend for several layers. In solubility product Symbol: Ks If an ionic the case of transition metal elements, ions solid is in contact with its saturated solu- may also form complexes by coordination tion, there is a dynamic equilibrium be- to the nearest layer of molecules. tween solid and solution: AB(s) ˆ A+(aq) + B–(aq) Solvay process /sol-vay/ (ammonia–soda The equilibrium constant for this is given process) An industrial process for making by sodium carbonate. The raw materials are [A+][B–]/[AB] calcium carbonate and sodium chloride

255 solvent

(with ammonia). The calcium carbonate is solving it in another (better) solvent that is heated: imiscible with the original solvent. → CaCO3 CaO + CO2 Carbon dioxide is bubbled into a solution solvent naphtha See naphtha. of sodium chloride saturated with ammonia, precipitating sodium hydrogencarbon- solvolysis /sol-vol-ă-sis/ A reaction be- ate and leaving ammonium chloride in tween a compound and the solvent in solution. The sodium hydrogencarbonate which it is dissolved. See also hydrolysis. is then heated: → 2NaHCO3 Na2CO3 + H2O + CO2 sorbitol /sor-bă-tol, -tohl/ (HOCH2- The ammonia is regenerated by heating the (CHOH)4CH2OH) A hexahydric alcohol ammonium chloride with the calcium that occurs in rose hips and rowan berries. oxide: It can be synthesized by the reduction of → 2NH4Cl + CaO CaCl2 + 2NH3 + glucose. Sorbitol is used to make vitamin C H2O (ascorbic acid) and surfactants. It is also used in medicines and as a sweetener (par- solvent /sol-vĕnt/ A liquid capable of dis- ticularly in foods for diabetics). It is an iso- solving other materials (solids, liquids, or mer of mannitol. gases) to form a solution. The solvent is generally the major component of the solu- sorption /sorp-shŏn/ Absorption of gases tion. Solvents can be divided into classes, by solids. the most important being: Polar. A solvent in which the molecules specific /spĕ-sif-ik/ Denoting a physical possess a moderate to high dipole moment quantity per unit mass. For example, vol- and in which polar and ionic compounds ume (V) per unit mass (m) is called specific are easily soluble. Polar solvents are usu- volume: ally poor solvents for non-polar com- V = Vm pounds. For example, water is a good In certain physical quantities the term solvent for many ionic species, such as does not have this meaning: for example, sodium chloride or potassium nitrate, and specific gravity is more properly called rel- polar molecules, such as the sugars, but ative density. does not dissolve paraffin wax. Non-polar. A solvent in which the mole- specific gravity See relative density. cules do not possess a permanent dipole moment and consequently will solvate specific heat capacity Symbol: c The non-polar species in preference to polar amount of heat needed to raise a unit mass species. For example, benzene and tetra- of a substance by one degree. It is measured chloromethane are good solvents for io- in joules per kilogram per Kelvin (J dine and paraffin wax, but do not dissolve kg–1K–1) in SI units. sodium chloride. α Amphiprotic. A solvent which undergoes specific rotatory power Symbol: m The self-ionization and can act both as a proton rotation of plane-polarized light in degrees donator and as an acceptor. Water is a produced by a 10 cm length of solution good example and ionizes according to: containing 1 g of a given substance per mil- + – 2H2O = H3O + OH liliter of stated solvent. The specific rota- Aprotic. A solvent which can neither ac- tory power is a measure of the optical cept nor yield protons. An aprotic solvent activity of substances in solution. It is mea- is therefore the opposite to an amphiprotic sured at 20°C using the D-line of sodium. solvent. spectra See spectrum. solvent extraction (liquid–liquid extraction) A method of removing a substance spectral line A particular wavelength of from solution by shaking it with and dis- electromagnetic radiation emitted or ab-

256 spelter sorbed by an atom, ion, or molecule. See lengths present in electromagnetic radia- line spectrum. tion. See also spectrometer. spectral series A group of related lines in spectroscopy /spek-tros-kŏ-pee/ 1. The the absorption or emission spectrum of a production and analysis of spectra. There substance. The lines in a spectral series are many spectroscopic techniques de- occur when the transitions all occur be- signed for investigating the electromag- tween one particular energy level and a set netic radiation emitted or absorbed by of different levels. See also Bohr theory. substances. Spectroscopy, in various forms, is used for analysis of mixtures, for spectrograph /spek-trŏ-graf, -grahf/ An identifying and determining the structures instrument for producing a photographic of chemical compounds, and for investigat- record of a spectrum. ing energy levels in atoms, ions, and molecules. In the visible and longer wavelength spectrographic analysis /spek-trŏ-graf- ultraviolet, transitions correspond to elec- ik/ A method of analysis in which the sam- tronic energy levels in atoms and mol- ple is excited electrically (by an arc or ecules. The shorter wavelength ultraviolet spark) and emits radiation characteristic of corresponds to transitions in ions. In the X- its component atoms. This radiation is ray region, transitions in the inner shells of passed through a slit, dispersed by a prism atoms or ions are involved. The infrared re- or a grating, and recorded as a spectrum, gion corresponds to vibrational changes in either photographically or photoelectri- molecules, with rotational changes at cally. The photographic method was longer wavelengths. 2. Any of various techniques for analysing widely used for qualitative and semiquan- the energy spectra of beams of particles or titative work but photoelectric detection for determining mass spectra. also allows wide quantitative application. spectrum /spek-trŭm/ (pl. spectra) 1. A spectrometer /spek-trom-ĕ-ter/ 1. An in- range of electromagnetic radiation emitted strument for examining the different wave- or absorbed by a substance under particu- lengths present in electromagnetic lar circumstances. In an emission spec- radiation. Typically, spectrometers have a trum, light or other radiation emitted by source of radiation, which is collimated by the body is analyzed to determine the par- a system of lenses and/or slits. The radia- ticular wavelengths produced. The emis- tion is dispersed by a prism or grating, and sion of radiation may be induced by a recorded photographically or by a photo- variety of methods; for example, by high cell. There are many types for producing temperature, bombardment by electrons, and investigating spectra over the whole absorption of higher-frequency radiation, range of the electromagnetic spectrum. etc. In an absorption spectrum a continu- Often spectrometers are called spectro- ous flow of radiation is passed through the scopes. sample. The radiation is then analyzed to 2. Any of various other instruments for an- determine which wavelengths are ab- alyzing the energies, masses, etc., of parti- sorbed. See also band spectrum; continu- cles. See mass spectrometer. ous spectrum; line spectrum. 2. In general, any distribution of a prop- spectrophotometer /spek-troh-foh-tom- erty. For instance, a beam of particles may ĕ-ter/ A form of spectrometer able to mea- have a spectrum of energies. A beam of sure the intensity of radiation at different ions may have a mass spectrum (the distri- wavelengths in a spectrum, usually in the bution of masses of ions). See mass spec- visible, infrared, or ultraviolet regions. trometer. spectroscope /spek-trŏ-skohp/ An instru- spelter Commercial zinc containing about ment for examining the different wave- 3% impurities, mainly lead.

257 spin spin A property of certain elementary par- bonic acid, which is able to react with lime- ticles whereby the particle acts as if it were stone rock (calcium carbonate) to give a so- spinning on an axis; i.e. it has an angular lution of calcium hydrogencarbonate. The momentum. Such particles also have a solution accumulates in drops on the roof magnetic moment. In a magnetic field the of caves and as it evaporates, the reaction spins line up at an angle to the field direc- is reversed causing calcium carbonate to be tion and precess around this direction. Cer- deposited. Over a very long period, the de- tain definite orientations to the field posits build up to give a stalactite hanging π direction occur such that msh/2 is the from the cavern roof. Water that drips component of angular momentum along onto the floor from the tip of the stalactite this direction. ms is the spin quantum num- also evaporates to leave a deposit of cal- ber, and for an electron it has values +1/2 cium carbonate. This gradually grows to and –1/2. h is the Planck constant. form a stalagmite. Stalagmites and stalactites can eventually meet to form a single spontaneous combustion The self-igni- rock pillar. tion of a substance that has a low ignition temperature. It occurs when slow oxida- standard cell A voltaic cell whose e.m.f. tion of the substance (such as a heap of is used as a standard. See Clark cell; We- damp straw or oily rags) builds up suffi- ston cadmium cell. cient heat for ignition to take place. standard electrode A half cell used for square-planar See complex. measuring electrode potentials. The hydrogen electrode is the basic standard but, in stabilization energy The difference in practice, calomel electrodes are usually energy between the delocalized structure used. and the conventional structure for a compound. For example, the stabilization en- standard pressure An internationally ergy of benzene is 150 kJ per mole, which agreed value; a barometric height of 760 represents the difference in energy between mmHg at 0°C; 101 325 Pa (approximately a Kekulé structure and the delocalized 100 kPa). This is sometimes called the at- structure: the delocalized form being of lower energy is therefore more stable. The mosphere (used as a unit of pressure). The stabilization energy can be determined by bar, used mainly when discussing the comparing the experimental value for the weather, is 100 kPa exactly. heat of hydrogenation of benzene with that calculated for Kekulé benzene from bond- standard solution A solution that con- energy data. tains a known weight of the reagent in a definite volume of solution. A standard stabilizer A substance added to prevent flask or volumetric flask is used for this chemical change (i.e. a negative catalyst). purpose. The solutions may be prepared by direct weighing for PRIMARY STANDARDS. If staggered conformation See conforma- the reagent is not available in a pure form tion. or is deliquescent the solution must be standardized by titration against another stainless steel See steel. known standard solution. stalactites and stalagmites /stal-ăk-tÿts standard state The standard conditions stal-ăg-mÿts, stă-lak-tÿts stă-lag-mÿys/ Pil- used as a reference system in thermody- lars of calcium carbonate found hanging namics: pressure is 101 325 Pa; tempera- from the ceiling (stalactites) and standing ture is 25°C (298.15 K); concentration is 1 on the floor (stalagmites) in limestone cav- mol. The substance under investigation erns. They form when water containing must also be pure and in its usual state, dissolved carbon dioxide forms weak car- given the above conditions.

258 steam reforming standard temperature An internation- The major distinctions between the ally agreed value for which many measure- states of matter depend on the kinetic ener- ments are quoted. It is the melting gies of their particles and the distances be- temperature of water, 0°C (273.15 K). See tween them. In solids, the particles have also STP. low kinetic energy and are closely packed; in gases they have high kinetic energy and stannane /stan-ayn/ (tin(IV) hydride; are very loosely packed; kinetic energy and SnH4) A colorless poisonous gas prepared separation of particles in liquids are inter- by the action of lithium tetrahydroalumi- mediate. nate(III) on tin(II) chloride. It is unstable, Solids have fixed shapes and volumes, decomposing immediately at 150°C. Stan- i.e. they do not flow, like liquids and gases, nane acts as a reducing agent. and they are difficult to compress. In solids the atoms or molecules occupy fixed posi- stannate /stan-ayt/ See tin. tions in space. In most cases there is a regular pattern of atoms – the solid is stannic chloride /stan-ik/ See tin(IV) crystalline. chloride. Liquids have fixed volumes (i.e. low compressibility) but flow to take up the stannic compounds Compounds of shape of the container. The atoms or mol- tin(IV). ecules move about at random, but they are quite close to one another and the motion stannite /stan-ÿt/ See tin. is hindered. Gases have no fixed shape or volume. stannous compounds /stan-ŭs/ Com- They expand spontaneously to fill the con- pounds of tin(II). tainer and are easily compressed. The molecules have almost free random motion. starch A polysaccharide that occurs ex- A plasma is sometimes considered to be clusively in plants. Starches are extracted a fourth state of matter. commercially from maize, wheat, barley, rice, potatoes, and sorghum. The starches stationary phase See chromatography. are storage reservoirs for plants; they can be broken down by enzymes to simple sug- statistical mechanics The branch of ars and then metabolized to supply energy physics and chemistry associated with needs. Starch is a dietary component of an- using statistical methods to relate the prop- imals. erties of a large number of microscopic Starch is not a single molecule but a particles, such as atoms and molecules, to mixture of amylose (water-soluble, blue the macroscopic properties of the system. color with iodine) and amylopectin (not water-soluble, violet color with iodine). steam distillation A method of isolating The composition is amylose 10–20%, or purifying substances by exploiting Dal- amylopectin 80–90%. ton’s law of partial pressures to lower the boiling point of the mixture. When two im- Stark effect The splitting of atomic spec- miscible liquids are distilled, the boiling tral lines because of the presence of an ex- point will be lower than that of the more ternal electric field. This phenomenon was volatile component and consequently will discovered by the German physicist Jo- be below 100°C if one component is water. hannes Stark (1874–1957) in 1913. The method is particularly useful for recovering materials from tarry mixtures. states of matter The three physical conditions in which substances occur: solid, steam reforming The conversion of a liquid, and gas. The addition or removal of methane–steam mixture at 900°C with a energy (usually in the form of heat) enables nickel catalyst into a mixture of carbon one state to be converted into another. monoxide and hydrogen. The mixture of

259 stearate

Steam distillation

gases (synthesis gas) provides a starting Step 1 – → material in a number of processes, e.g. the OCl (aq) + H2O(l) HOCl(aq) + manufacture of methanol. OH–(aq) Step 2 stearate /stee-ă-rayt/ A salt or ester of I–(aq) + HOCl(aq) → HOI(aq) + Cl–(aq) stearic acid; an octadecanoate. Step 3 – → – OH (aq) + HOI(aq) H2O(l) + OI (aq) stearic acid /stee-a-rik/ See octadecanoic acid. steradian /sti-ray-dee-ăn/ Symbol: sr The SI unit of solid angle. The surface of a steatite /stee-ă-tÿt/ See soapstone. sphere, for example, subtends a solid angle of 4π at its center. The solid angle of a cone steel An alloy of iron with small amounts is the area intercepted by the cone on the of carbon and, often, other metals. Carbon surface of a sphere of unit radius. steels contain 0.05–1.5% carbon – the more carbon, the harder the steel. Alloy stereochemistry /ste-ree-oh-kem-iss-tree, steels contain carbon but also contain steer-ee-/ The branch of chemistry con- small amounts of certain other elements; cerned with the shapes of molecules and for example chromium, manganese, and the way these affect the chemical proper- vanadium. Their properties depend on the ties. composition. Stainless steels, for instance, are resistant to corrosion. The main non- stereoisomerism /ste-ree-oh-ÿ-som-ĕ-riz- ferrous constituent is chromium (10–25%) ăm, steer-ee-/ See isomerism. with up to 0.7% carbon. stereospecific /ste-ree-oh-spĕ-sif-ik, steer- step An elementary stage in a chemical re- ee-/ Describing a chemical reaction involv- action, in which energy may be transferred ing an asymmetric atom (usually carbon) from one molecule to another, bonds may that results in the formation of only one be broken or formed, or electrons may be geometric isomer. See isomerism; optical transferred. For example, in the reaction activity. between hypochlorite ions and iodide ions in aqueous solution there are three distinct stereospecific polymer See polymeriza- steps: tion.

260 strontium

→ steric effect /ste-rik, steer-ik/ An effect in RCH(CN)OH + NH3 which the shape of a molecule influences its RCH(CN)(NH2) + H2O reactions. A particular example occurs in Acid hydrolysis of the cyanide group then molecules containing large groups, which produces the amino acid → hinder the approach of a reactant (steric RCH(CN)(NH2) hindrance). RCH(COOH)(NH2) The method is a general synthesis for α- steric hindrance See steric effect. amino acids (with the –NH2 and –COOH groups on the same carbon atom). steroid /steer-oid/ Any member of a group of biochemical compounds having a com- strong acid An acid that is almost complex basic ring structure. Examples are cor- pletely dissociated into its component ions ticosteroid hormones (produced by the in solution. Compare weak acid. adrenal gland), sex hormones (proges- terone, androgens, and estrogens), bile strong base A base that is completely or acids, and sterols (such as cholesterol). almost completely dissociated into its component ions in solution. sterol /steer-ol, -ohl/ A steroid with long aliphatic side chains (8–10 carbons) and at strontia /stron-shee-ă/ See strontium least one hydroxyl group. They are lipid- oxide. soluble and often occur in membranes. Ex- amples are cholesterol and ergosterol. strontium /stron-shee-ŭm, -tee-/ A soft low-melting reactive metal; the fourth still An apparatus for distillation. member of group 2 of the periodic table and a typical alkaline-earth element. The /stoi-kee-ŏ- stoichiometric coefficient electronic configuration is that of krypton met-rik/ See chemical equation. with two additional outer 5s electrons. Strontium and barium are both of low stoichiometry /stoi-kee-om-ĕ-tree/ The abundance in the Earth’s crust, strontium proportions in which elements form com- occurring as strontianite (SrCO ) and ce- pounds. A stoichiometric compound is one 3 lestine (SrSO ). in which the atoms have combined in small 4 The element is produced industrially by whole numbers. roasting the carbonate to give the oxide ° See accumulator. (800 C) and then reducing with aluminum, storage battery → 3SrO + 2Al Al2O3 + 2Sr STP (NTP) Standard temperature and Strontium has a low ionization poten- pressure. Conditions used internationally tial, is large, and is therefore very elec- when measuring quantities that vary with tropositive. The chemistry of strontium both pressure and temperature (such as the metal is therefore characterized by high re- density of a gas). The values are 101 325 activity of the metal. The properties of Pa (approximately 100 kPa) and 0°C strontium fall into sequence with other al- (273.15 K). See also standard pressure; kaline earths. Thus it reacts directly with standard temperature. oxygen, nitrogen, sulfur, the halogens, and hydrogen to form respectively the oxide straight chain See chain. SrO, nitride Sr3N2, sulfide SrS, halides SrX2, and hydride SrH2, all of which are Strecker synthesis /strek-er/ A method of largely ionic in character. The oxide SrO synthesizing amino acids. Hydrogen and the metal react readily with water to cyanide forms an addition product form the hydroxide Sr(OH)2, which is (cyanohydrin) with aldehydes: basic and mid-way between Ca(OH)2 and RCHO + HCN → RCH(CN)OH Ba(OH)2 in solubility. The carbonate and With ammonia further substitution occurs: sulfate are both insoluble.

261 strontium bicarbonate

As the metal is very electropositive the position of strontium carbonate, hydrox- salts are never much hydrolyzed in solution ide, or nitrate. Strontium oxide is soluble in and the ions are largely solvated as water, forming an alkaline solution be- 2+ [Sr(H2O)6] . cause of the attraction between the oxide Symbol: Sr; m.p. 769°C; b.p. 1384°C; ions and protons from the water: ° 2– → – r.d. 2.54 (20 C); p.n. 38; r.a.m. 87.62. O + H2O 2OH strontium bicarbonate See strontium strontium sulfate (SrSO4) A white spar- hydrogencarbonate. ingly soluble salt that occurs naturally as the mineral celestine. It can be prepared by strontium carbonate (SrCO3) A white dissolving strontium oxide, hydroxide, or insoluble solid that occurs naturally as the carbonate in sulfuric acid. It is used as a mineral strontianite. It can be prepared by substitute for barium sulfate in paints. passing carbon dioxide over strontium oxide or hydroxide or by passing the gas structural formula The formula of a through a solution of a strontium salt. compound showing the numbers and types Strontium carbonate is then formed as a of atoms present, together with the way in precipitate. It is used as a slagging agent in which these are arranged in the molecule. certain metal furnaces and to produce a red Often this can be done by grouping the flame in fireworks. atoms, as in the structural formula of ethanoic acid CH3.CO.OH. Compare em- strontium chloride (SrCl2) A white solid pirical formula; molecular formula. obtained directly from strontium and chlorine or by passing chlorine over heated structural isomerism See isomerism. strontium oxide. It is used in fireworks to give a red flame. The hexahydrate styrene /stÿ-reen/ See phenylethene. (SrCl2.6H2O) is prepared by the neutralization of hydrochloric acid by strontium sublimate /sub-lă-mayt/ A solid formed hydroxide or carbonate. by sublimation. strontium hydrogencarbonate (stron- sublimation /sub-lă-may-shŏn/ The con- tium bicarbonate; Sr(HCO3)2) A com- version of a solid into a vapor without the pound present in solutions formed by the solid first melting. For instance (at stan- action of carbon dioxide on a suspension in dard pressure) iodine, solid carbon diox- cold water of strontium carbonate, to ide, and ammonium chloride sublime. At which it reverts on heating: certain conditions of external pressure and SrCO3 + CO2 + H2O = Sr(HCO3)2 temperature an equilibrium can be established between the solid phase and vapor strontium hydroxide (Sr(OH)2) A solid phase. that normally occurs as the octahydrate (Sr(OH)2.8H2O), which is prepared by sub-shell A subdivision of an electron crystallizing an aqueous solution of stron- shell. It is a division of the orbitals that tium oxide. Strontium hydroxide is readily make up a shell into sets of orbitals, which soluble in water and aqueous solutions are are degenerate (i.e. have the same energy) strongly basic. It is used in the purification in the free atom. For example, in the third of sugar. shell or M-shell there are the 3s, 3p, and 3d sub-shells of which the latter two are 3- strontium nitrate (Sr(NO3)2) A colorless and 5-degenerate respectively. crystalline compound, often used in pyrotechnics to produce a bright red flame. substituent /sub-stich-û-ĕnt/ An atom or group substituted for another in a com- strontium oxide (strontia; SrO) A gray- pound. Often the term is used for groups ish-white powder prepared by the decom- that have replaced hydrogen in organic

262 sugar compounds; for example, in benzene deriv- sugar cane and sugar beet. Sucrose is a dis- atives. accharide formed from a glucose unit and a fructose unit. It is hydrolyzed to a mix- substitution reaction A reaction in ture of fructose and glucose by the enzyme which an atom or group of atoms in an or- invertase. Since this mixture has a different ganic molecule is replaced by another atom optical rotation (levorotatory) than the or group. The substitution of a hydrogen original sucrose, the mixture is called in- atom in an alkane by a chlorine atom is an vert sugar. example. Substitution reactions fall into three major classes depending upon the na- sugar (saccharide) One of a class of sweet- ture of the attacking substituent. tasting simple CARBOHYDRATES. Sugars Nucleophilic substitution: the attacking have molecules consisting of a chain of car- substituent is a nucleophile. Such reactions bon atoms with –OH groups attached, and are very common with alcohols and halo- either an aldehyde or ketone group. They gen compounds, in which the electron-de- can exist in a chain form or in a ring ficient carbon atom attracts the formed by reaction of the ketone or alde- nucleophile and the leaving group readily hyde group with an OH group. Monosac- exists alone. Examples are the hydrolysis charides are simple sugars that cannot be of a haloalkane and the chlorination of an hydrolyzed to sugars with fewer carbon alcohol: – → – C2H5Cl + OH C2H5OH + Cl → C2H5OH + HCl C2H5Cl + H2O CH2OH Electrophilic substitution: the attacking O substituent is an electrophile. Such reactions are common in aromatic compounds, in which the electron-rich ring attracts the OH electrophile. The nitration of benzene in HO OH + which the electrophile is NO2 is an example: OH + → + C6H6 + NO2 C6H5NO2 + H Free-radical substitution: a free radical is glucose – a pyranose ring the attacking substituent. Such reactions can be used with compounds that are inert to either nucleophiles or electrophiles, for O HOCH CH OH instance the halogenation of an alkane: 2 2 → CH4 + Cl2 CH3Cl + HCl The term ‘substitution’ is very general HO and several reactions that can be consid- OH ered as substitutions are more normally given special names (e.g. esterification, hy- OH drolysis, and nitration). See also elec- fructose – in a furanose ring form trophilic substitution; nucleophilic substitution. O HOCH2 substrate /sub-strayt/ A material that is acted on by a catalyst. succinic acid /suk-sin-ik/ See butanedioic OH acid. OH OH sucrose /soo-krohs/ (cane sugar; ribose – a furanose ring C12H22O11) A sugar that occurs in many plants. It is extracted commercially from Sugars

263 sulfa drugs

H H CH2OH CH2OH O O HO H HO H H OH H H HO OH HO OH OH H H H α–D–glucose β–D–glucose Glucose — a monosaccharide sugar

CH2OH O O H H HOCH2 H H OH H O H HO HO CH2OH

OH OH H

Sucrose — a disaccharide sugar

Sugar: monosaccharides and disaccharides atoms. Two or more monosaccharide units 2. See thioether. can be linked in disaccharides, trisaccha- rides, etc. sulfinate /sul-fă-nayt, -nit/ See dithionite. Monosaccharides are also classified according to the number of carbon atoms: a sulfinic acid /sul-fin-ik/ See dithionous pentose has five carbon atoms and a hex- acid. ose six. Monosaccharides with aldehyde groups are aldoses; those with ketone sulfite /sul-fÿt/ A salt or ester of sulfurous groups are ketoses. Thus, an aldohexose is acid. a hexose with an aldehyde group; a ketopentose is a pentose with a ketone group, sulfonamide /sul-fon-ă-mÿd/ A type of etc. organic compound with the general for- The ring forms of monosaccharides are mula R.SO .NH . Sulfonamides, which are derived by reaction of the aldehyde or ke- 2 2 amides of sulfonic acids, are active against tone group with one of the carbons at the bacteria, and some are used in pharmaceu- other end of the chain. It is possible to have ticals (‘sulfa drugs’). a six-membered (pyranose) ring or a five- membered (furanose) ring. See also polysul-fŏ-nayt saccharide. sulfonate / / A salt or ester of sulfonic acid. See sulfonic acid. sulfa drugs /sul-fă/ See sulfonamide. sulfonation /sul-fŏ-nay-shŏn/ A reaction sulfate /sul-fayt/ A salt or ester of sulfu- introducing the –SO2OH (sulfonic acid) ric(VI) acid. group into an organic compound. Sulfona- tion of aromatic compounds is usually ac- sulfide /sul-fÿd/ 1. A compound of sulfur complished by refluxing with concentrated with a more electropositive element. Sim- sulfuric acid for several hours. The attack- 2– ple sulfides contain the ion S . Polysul- ing species is SO3 (sulfur(VI) oxide) and the fides can also be formed containing ions reaction is an example of electrophilic sub- 2– with chains of sulfur atoms (Sx ). stitution.

264 sulfoxide

Glucose (an aldohexose) 6 6 CH OH CH OH 1 2 2 H C O 5 5 C O C O 2 H C OH H H H OH H H 1 1 3 C C C C HO C O 4 OH H 4 OH H 4 HO OH HO H H C OH C C C C 3 2 3 2 5 H C OH H OH H OH

6 α β CH2OH -glucose -glucose straight-chain form ring forms

Fructose (a ketohexose)

1 H C OH

2 C O 6 1 HOCH2 O CH2OH HO 3 C H 5 2 C H OH C 4 H C OH HO OH C C 5 4 3 H C OH 6 OH H CH2OH

straight-chain form ring form

Sugar: straight-chain and ring forms

sulfonic acid /sul-fon-ik/ A type of or- zene ring; the –SO2.OH group directs sub- ganic compound containing the –SO2.OH stituents into the 3-position. group. The simplest example is benzenesulfonic acid (C6H5SO2OH). Sulfonic acids sulfonium compound /sul-foh-nee-ŭm/ are strong acids. Electrophilic substitution An organic compound of general formula can introduce other groups onto the ben- R3SX, where R is an organic radical and X is an electronegative radical or element; it + O contains the ion R3S . An example is di- ethylmethylsulfonium chloride, (C2H5)2- + – CH3.S Cl , made by reacting diethyl S OH sulfide with chloromethane.

sulfoxide /sul-foks-ÿd, -id/ An organic O compound of general formula RSOR′, Sulfonic acid where R and R′ are organic radicals. An

265 sulfur example is dimethyl sulfoxide, (CH3)2SO, S2F2, SF4, SF6, S2F10; three chlorides, S2Cl2, commonly used as a solvent. SCl2, SCl4; a bromide S2Br2, but no iodide. Apart from SF6, which is surprisingly sta- sulfur /sul-fer/ A low melting non-metallic ble and inert, the halides are generally sus- solid, yellow colored in its common forms; ceptible to hydrolysis to give commonly the second member of group 16 of the pe- SO2, sometimes H2S, and the hydrogen riodic table. It has the electronic configura- halide. The halides SF4, S2Cl2, and SCl2 are tion [Ne]3s23p4. frequently used as selective fluorinating Sulfur occurs in the elemental form in agents and chlorinating agents in organic Sicily and some southern states of the USA, chemistry. The chlorides are also industri- and in large quantities in combined forms ally important for hardening rubbers. Sul- fur hexafluoride may be prepared by direct such as sulfide ores (FeS2) and sulfate rocks reaction of the elements but SF is prepared (CaSO4). It forms about 0.5% of the 4 Earth’s crust. Elemental sulfur is extracted by fluorinating SCl2 with NaF. In a limited commercially by the Frasch process, supply of chlorine, sulfur combines to give named for the German–American chemist sulfur monochloride, S2Cl2; in excess chlo- Herman Frasch (1851–1914), in which su- rine at higher temperatures the dichloride perheated steam is forced down the outer is formed, → of three concentric tubes leading into the 2S + Cl2 S2Cl2 → deposit. This causes the sulfur to melt; then S2Cl2 + Cl2 2SCl2 air is blown down the central tube causing In addition to these binary halides, sul- molten sulfur to be forced out of the well to fur forms two groups of oxyhalides; the be collected and cooled at the well head. sulfur dihalide oxides (thionyl halides), SOX (F, Cl, and Br, but not I), and the sul- The large amount of sulfur obtained from 2 fur dihalide dioxides (sulfuryl halides), smelting of sulfide ores or roasting of sul- SO X (F and Cl, but not Br and I). fates is not obtained as elemental sulfur but 2 2 Most metals react with sulfur to form is used directly as SO /SO for conversion 2 3 sulfides of which there are a large number to sulfuric acid (contact process). of structural types. With electropositive el- Sulfur exhibits allotropy and its struc- ements of groups I and II the sulfides are ture in all phases is quite complex. The largely ionic (S2–) in the solid phase. Hy- common crystalline modification, rhombic drolysis occurs in solution thus: sulfur, is in equilibrium with a triclinic 2– → – – ° S + H2O SH + OH modification above 96 C. Both have struc- Most transition metals form sulfides, tures based on S8-rings but the crystals are which although formally treated as FeS, quite different. If molten sulfur is poured CoS, NiS, etc., are largely covalent and fre- into water a dark red ‘plastic’ form is ob- quently non-stoichiometric. tained in a semielastic form. The structure In addition to the complexities of the appears to be a helical chain of S atoms. Se- binary compounds with metals, sulfur lenium and tellurium both have a gray forms a range of binary compounds with ‘metal-like’ modification but sulfur does elements such as Si, As, and P, which may not have this form. be polymeric and generally of rather com- Sulfur reacts directly with hydrogen but plex structure, e.g. (SiS4)n, (SbS3)n, N4S4, the position of the equilibrium at normal As4S4, P4S3. temperatures precludes its use as a prepar- Sulfur also forms a wide range of or- ative method for hydrogen sulfide. The el- ganic sulfur compounds, most of which ement burns readily in oxygen with a have the typically revolting smell of H2S. characteristic blue flame to form sulfur(IV) Symbol: S; m.p. 112.8°C; b.p. 444.6°C; oxide (SO2) and traces of sulfur(VI) oxide r.d. 2.07; p.n. 16; r.a.m. 32.066. (SO3). Sulfur also forms a large number of oxy-acid species, some containing peroxy- sulfur dichloride dioxide /dÿ-oks-ÿd, -id/ groups and some with two or more S- (sulfuryl chloride; SO2Cl2) A colorless atoms. It forms four distinct fluorides, fuming liquid formed by the reaction of

266 superconductivity chlorine with sulfur(IV) oxide in sunlight. dichromate(VI) ions to green chrom- It is used as a chlorinating agent. ium(III) ions. sulfur dichloride oxide (thionyl chlo- sulfur(IV) oxide (sulfur dioxide; SO2) A ride; SOCl2) A colorless fuming liquid colorless choking gas prepared by burning formed by passing sulfur(IV) oxide over sulfur or heating metal sulfides in air, or by phosphorus(V) chloride and distilling the treating a sulfite with an acid. It is a pow- mixture obtained. Sulfur dichloride oxide erful reducing agent, used as a bleach. It is used in organic chemistry to introduce dissolves in water to form sulfurous acid chlorine atoms (for example, into ethanol (sulfuric(IV) acid) and combines with oxy- to form monochloroethane), the organic gen, in the presence of a catalyst, to form product being easily isolated as the other sulfur(VI) oxide. This latter reaction is im- products are gases. portant in the manufacture of sulfuric(VI) acid. sulfur dioxide /dÿ-oks-ÿd, -id/ See sulfur(IV) oxide. sulfur(VI) oxide (sulfur trioxide; SO3) A fuming volatile white solid prepared by sulfuretted hydrogen /sul-fyŭ-ret-id/ See passing sulfur(IV) oxide and oxygen over hydrogen sulfide. hot vanadium(V) oxide (acting as a catalyst) and cooling the product in ice. Sul- sulfuric(IV) acid /sul-fyoor-ik/ See sulfur(VI) oxide reacts vigorously with water furous acid. to form sulfuric acid. See also contact process. sulfuric(VI) acid (oil of vitriol; H SO ) A 2 4 /trÿ-oks-ÿd/ See sulfur(VI) colorless oily liquid manufactured by the sulfur trioxide oxide. CONTACT PROCESS. The concentrated acid is diluted by adding it slowly to water, with sulfuryl /sul-fŭ-răl, -yŭ-, -reel/ Describing careful stirring. Concentrated sulfuric acid a compound containing the group =SO . acts as an oxidizing agent, giving sulfur(IV) 2 oxide as the main product, and also as a sulfuryl chloride /sul-fŭ-răl, -yŭ-, -reel/ dehydrating agent. The diluted acid acts as See sulfur dichloride dioxide. a strong dibasic acid, neutralizing bases and reacting with active metals and car- superacid /soo-per-ass-id/ An acid with a bonates to form sulfates. high proton-donating ability. Superacids Sulfuric acid is used in the laboratory to are substances such as HF–SbF3 and dry gases (except ammonia), to prepare ni- HSO3–SbF5. Sometimes known as magic tric acid and ethene, and to absorb alkenes. acids, they are able to produce carbenium In industry, it is used to manufacture fertil- ions from some saturated hydrocarbons. izers (e.g. ammonium sulfate), rayon, and detergents, to clean metals, and in vehicle superconduction /soo-per-kŏn-duk-shŏn/ batteries. The property of zero resistance exhibited by certain metals and metallic compounds sulfur monochloride /mon-ŏ-klor-ÿd, at low temperatures. Metals conduct at -id, -kloh-rÿd, -rid/ See disulfur dichloride. temperatures close to absolute zero but a number of compounds are now known sulfurous acid /sul-fyoor-ŭs/ (sulfuric(IV) that conduct at higher (liquid-nitrogen) acid; H2SO3) A weak acid found only in temperatures. Synthetic organic supercon- solution, made by passing sulfur(IV) oxide ductors have also been produced. into water. The solution is unstable and smells of sulfur(IV) oxide. It is a reducing superconductivity /soo-per-kon-duk-tiv- agent, converting iron(III) ions to iron(II) ă-tee/ The property of zero electrical resis- ions, chlorine to chloride ions, and orange tance exhibited by certain metals and

267 supercooling metallic compounds at low temperatures. supplementary units See dimensionless Metals show superconductivity at temper- units. atures close to absolute zero but a number of ceramic metal oxides are now known supramolecular chemistry /soo-pră-mŏ- that are superconducting at higher (94K or lek-yŭ-ler/ A branch of chemistry con- better) temperatures. Synthetic organic su- cerned with the synthesis and study of large perconductors have also been produced. structures consisting of molecules assem- bled together in a definite pattern. In a supercooling /soo-per-koo-ling/ The supramolecule the molecular units (which cooling of a liquid at a given pressure to a are sometimes known as synthons) are temperature below its melting temperature joined by intermolecular bonds – i.e. by hy- at that pressure without solidifying it. The drogen bonds or by ionic attractions. A liquid particles lose energy but do not particular interest in supramolecular re- spontaneously fall into the regular geomet- search is the idea of self-assembly – i.e. that rical pattern of the solid. A supercooled liq- the molecules form well-defined structures uid is in a metastable state and will usually spontaneously as a result of their geometry solidify if a small crystal of the solid is in- and chemical properties. In this way, troduced to act as a ‘seed’ for the forma- supramolecular chemistry is ‘chemistry be- tion of crystals. As soon as this happens, yond molecules’. the temperature returns to the melting tem- There are various different examples of perature until the substance has completely supramolecular structures. For instance, solidified. single layers of carboxylic acid molecules held by hydrogen bonds may form two-di- superfluidity /soo-per-floo-id-ă-tee/ A mensional crystalline structures with novel property of liquid HELIUM at very low tem- electrical properties. Large organic poly- peratures. At 2.186 K liquid helium makes meric structures may be formed in which a a transition to a superfluid state, which has number of individual chains radiate from a a high thermal conductivity and flows central point or region. These polymers are without friction. called dendrimers and they have a number of possible applications. Another type of superheating /soo-per-hee-ting/ The rais- supramolecule is a helicate, which has a ing of a liquid’s temperature above its boil- double helix made of two chains of ing temperature, by increasing the bipyridyl units held by copper ions along pressure. the axis. The structure is analogous to the double helix of DNA. See also host–guest supernatant /soo-per-nay-tănt/ Denoting chemistry. a clear liquid that lies above a sediment or a precipitate. supramolecule /soo-pră-mol-ĕ-kyool/ See supramolecular chemistry. superoxide /soo-per-oks-ÿd/ An inor- – ganic compound containing the O2 ion. surfactant /ser-fak-tănt/ A substance that lowers surface tension and has properties superphosphate /soo-per-fos-fayt/ A of wetting, foaming, detergency, disper- mixture – mainly calcium hydrogen phos- sion, and emulsification. phate and calcium sulfate – used as a fertilizer. It is made from calcium phosphate suspension A system in which small par- and sulfuric acid. ticles of a solid or liquid are dispersed in a liquid or gas. supersaturated solution /soo-per-sach-ŭ- ray-tit/ See saturated solution. symbol, chemical See chemical symbol. supersaturated vapor See saturated syndiotactic polymer See polymeriza- vapor. tion.

268 Système International d’Unités syn-isomer /sin ÿ-sŏ-mer/ See isomerism. Synthesis gas is a useful starting material for the manufacture of a number of or- synthesis /sin-th’ĕ-sis/ The preparation of ganic compounds. chemical compounds from simpler compounds. synthon /sin-thon/ See retrosynthetic analysis. synthesis gas A mixture of carbon monoxide and hydrogen produced by Système International d’Unités /see- steam reforming of natural gas. stem an-tair-nas-yo-nal doo-nee-tay/ See SI → CH4 + H2O CO + 3H2 units.

269 T

tactic polymer See polymerization. tartaric acid /tar-ta-rik/ A crystalline hydroxy carboxylic acid with the formula: talc /tal’k/ (French chalk) An extremely HOOC(CHOH)2COOH soft greenish or white mineral, a hydrous Its systematic name is 2,3-dihydroxy- silicate of magnesium. Purified it is sold as butanedioic acid. See also optical activity. talcum powder, and it is used as a lubricant, a filler (in paint and rubber) and an tartrate /tar-trayt/ A salt or ester of tar- ingredient of some ceramics. taric acid. tannic acid /tan-ik/ See tannin. tautomerism /taw-tom-ĕ-riz-ăm/ Iso- merism in which each isomer can convert tannin /tan-in/ Any of several yellow or- into the other, so that the two isomers are ganic compounds found in vegetable in equilibrium. The isomers are called tau- sources such as bark of trees, oak galls, and tomers. Tautomerism often results from tea. They are used in tanning animal skins the migration of a hydrogen atom. See to make leather and as mordants in dyeing. keto–enol tautomerism. Tannic acid (a type of tannin) is a white solid heterocyclic organic acid extracted TCCD See dioxins. from oak galls and used for making dyes and inks. technetium /tek-nee-shee-ŭm/ A transition metal that does not occur naturally on tantalum /tan-tă-lŭm/ A silvery transition Earth. It is produced artificially by bom- element. It is strong, highly resistant to cor- barding molybdenum with neutrons and rosion, and is easily worked. Tantalum is also during the fission of uranium. It is ra- used in turbine blades and cutting tools dioactive. and in surgical and dental work. Symbol: Tc; m.p. 2172°C; b.p. 4877°C; Symbol: Ta; m.p. 2996°C; b.p. 5425 ± r.d. 11.5 (est.); p.n. 43; r.a.m. 98.9063 100°C; r.d. 16.654 (20°C); p.n. 73; r.a.m. (99Tc); most stable isotope 98Tc (half-life 180.9479. 4.2 × 106 years). tar (bitumen) A dark oily viscous liquid Teflon (Trademark) The synthetic poly- obtained by the destructive distillation of mer polytetrafluoroethane. coal or the fractionation of PETROLEUM. Tars are mixtures consisting mainly of telluride /tel-yŭ-rÿd, -rid/ A compound of high-molecular weight hydrocarbons and TELLURIUM and another element. phenols. tellurium /te-loor-ee-ŭm/ A brittle silvery tartar emetic /tar-ter i-met-ik/ (potassium metalloid element belonging to group 16 of antimonyl tartrate; KSbO(C4H4O6). the periodic table. It is found native and in ¼ H2O) A poisonous compound of anti- combination with metals. Tellurium is mony, which is used as an emetic in medi- used mainly as an additive to improve the cine and as a mordant in dyeing and as an qualities of stainless steel and various insecticide. metals.

270 tetrachloromethane

Symbol: Te; m.p. 449.5°C; b.p. terephthalic acid /te-ref-thal-ik/ See ben- 989.8°C; r.d. 6.24 (20°C); p.n. 52; r.a.m. zene-1,4-dicarboxylic acid. 127.6. ternary compound /ter-nă-ree/ A chemi- temperature scale A practical scale for cal compound formed from three elements; measuring temperature. A temperature e.g. Na2SO4 or LiAlH4. scale is determined by fixed temperatures (fixed points), which are reproducible sys- terpene /ter-peen/ Any of a class of nat- tems assigned an agreed temperature. On ural unsaturated hydrocarbons with for- the Celsius scale the two fixed points are mulae (C5H8)n, found in plants. Terpenes the temperature of pure melting ice (the ice consist of isoprene units, temperature) and the temperature of pure CH2=C(CH3)CH=CH2. boiling water (the steam temperature). The Monoterpenes have two units (C10H16), difference between the fixed points is the diterpenes four units (C20H32), triterpenes fundamental interval of the scale, which is three units (C30H48), etc. Sesquiterpenes subdivided into temperature units. The In- have three isoprene units (C15H24). ternational Temperature Scale has 11 fixed points that cover the range 13.81 kelvin to tertiary alcohol See alcohol. 1337.58 kelvin. tertiary amine See amine. temporary hardness A type of water hardness caused by the presence of dis- tertiary structure See protein. solved calcium, iron, and magnesium hy- /ter-vay-lĕnt/ (trivalent) Having drogencarbonates. This form of hardness tervalent a valence of three. can be removed by boiling the water. Tem- porary hardness arises because rainwater Terylene /te-ră-leen/ (Trademark) A poly- combines with carbon dioxide from the at- mer made by condensing benzene-1,4-di- mosphere to form weak carbonic acid. carboxylic acid (terephthalic acid) and This reacts with carbonate rocks, such as ethane-1,2-diol (ethylene glycol), used for limestone, to produce calcium hydrogen- making fibers for textiles. carbonate, which then goes into solution. When this solution is heated, the complete tesla /tess-lă/ Symbol: T The SI unit of reaction sequence is reversed so that cal- magnetic flux density, equal to a flux den- cium carbonate is precipitated. If this is not sity of one weber of magnetic flux per removed, it will accumulate in boilers and square meter. 1 T = 1 Wb m–2. The unit is hot-water pipes and reduce their efficiency. named for the Croatian–American physi- Compare permanent hardness. See also cist Nikola Tesla (1856–1943). water softening. tetracarbonyl nickel(0) /tet-ră-kar-bŏ- 12 tera- Symbol: T A prefix denoting 10 . năl/ See nickel carbonyl. For example, 1 terawatt (TW) = 1012 watts (W). tetrachloroethene /tet-ră-klor-oh-eth- een, -kloh-roh-/ (ethylene tetrachloride; ter-bee-ŭm terbium / / A soft ductile mal- tetrachloroethylene; CCl2:CCl2) A color- leable silvery rare element of the lan- less poisonous liquid organic compound (a thanoid series of metals. It occurs in haloalkene) used as a solvent in dry clean- association with other lanthanoids. One of ing and as a de-greasing agent. its few uses is as a dopant in solid-state devices. tetrachloroethylene /tet-ră-klor-oh-eth- Symbol: Tb; m.p. 1356°C; b.p. 3123°C; ă-leen, -kloh-roh-/ See tetrachloroethene. r.d. 8.229 (20°C); p.n. 65; r.a.m. 158.92534. tetrachloromethane /tet-ră-klor-oh-

271 tetraethyl lead meth-ayn/ (carbon tetrachloride; CCl4) A atoms or molecules by the action of heat. colorless nonflammable liquid made by the Often it is temporary and reversible. chlorination of methane. Its main use is as a solvent. thermite /ther-mÿt/ (thermit) A mixture of aluminum powder and (usually) iron(III) tetraethyl lead /tet-ră-eth-ăl/ See lead oxide. When ignited the oxide is reduced; tetraethyl. the reaction is strongly exothermic and molten iron is formed: → tetrafluoroethene /tet-ră-floo-ŏ-roh-eth- 2Al + Fe2O3 Al2O3 + 2Fe een/ (CF2:CF2) A gaseous organic com- Thermite is used in incendiary bombs pound (a fluorocarbon and a haloalkene) and for welding steel. See also Gold- used to make the plastic polytetrafluo- schmidt process. roethene (PTFE). See polytetrafluoroethene. thermochemistry /ther-moh-kem-iss-tree/ The branch of chemistry concerned with tetragonal crystal /te-trag-ŏ-năl/ See heats of reaction, solvation, etc. crystal system. thermodynamics /ther-moh-dÿ-nam-iks/ tetrahedral compound /tet-ră-hee-drăl/ The study of heat and other forms of en- A compound such as methane, in which an ergy and the various related changes in atom has four bonds directed towards the physical quantities such as temperature, corners of a regular tetrahedron. The an- pressure, density, etc. gles between the bonds in such a com- The first law of thermodynamics states pound are about 109°. that the total energy in a closed system is conserved (constant). In all processes en- tetrahydrate /tet-ră-hÿ-drayt/ A crys- ergy is simply converted from one form to talline hydrated compound containing four another, or transferred from one system to molecules of water of crystallization per another. molecule of compound. See also complex. A mathematical statement of the first law is: tetrahydrofuran /tet-ră-hÿ-droh-fyoo- δQ = δU + δW δ ran, -fyoo-ran/ (THF, C4H8O) A colorless Here, Q is the heat transferred to the liquid widely used as a solvent and for system, δU the change in internal energy making polymers. (resulting in a rise or fall of temperature), and δW is the external work done by the tetravalent /tet-ră-vay-lĕnt, te-trav-ă-/ system. (quadrivalent) Having a valence of four. The second law of thermodynamics can be stated in a number of ways, all of which thallium /thal-ee-ŭm/ A soft malleable are equivalent. One is that heat cannot pass grayish metallic element belonging to from a cooler to a hotter body without group 13 of the periodic table. It is found some other process occurring. Another is in lead and cadmium ores, and in pyrites the statement that heat cannot be totally (FeS2). Thallium is highly toxic and was converted into mechanical work, i.e. a heat used previously as a rodent and insect poi- engine cannot be 100% efficient. son. Various compounds are now used in The third law of thermodynamics states photocells, infrared detectors, and low- that the entropy of a substance tends to melting glasses. zero as its thermodynamic temperature ap- Symbol: Tl; m.p. 303.5°C; b.p. 1457°C; proaches zero. r.d. 11.85 (20°C); p.n. 81; r.a.m. Often a zeroth law of thermodynamics 204.3833. is given: that if two bodies are each in thermal equilibrium with a third body, then thermal dissociation The decomposition they are in thermal equilibrium with each of a chemical compound into component other. This is considered to be more funda-

272 thixotropy mental than the other laws because they as- The components are identified by compar- sume it. See also Carnot cycle; entropy. ing the distance they have traveled up the plate with standard solutions that have thermodynamic temperature Symbol: T been run simultaneously, or by computing A temperature measured in kelvins. See an RF value. also absolute temperature. thio alcohol /th’ÿ-oh/ See thiol. thermoplastic polymer /ther-moh-plas- tik/ See polymer. thiocarbamide /th’ÿ-oh-kar-bă-mÿd, -mid/ (thiourea; NH CSNH ) A colorless ther-moh-set- 2 2 thermosetting polymer / crystalline organic compound (the sulfur ing/ See polymer. analog of urea). It is converted to the inorganic compound ammonium thiocyanate THF See tetrahydrofuran. on heating. It is used as a sensitizer in photography and in medicine. thiazine /th’ÿ-ă-zeen/ (C4H4NS) Any of a group of heterocyclic organic compounds that have a six-membered ring containing thioether /th’ÿ-oh-ee-ther/ An organic ′ four carbon atoms, one nitrogen atom, and sulfide; a compound of the type RSR . one sulfur atom. thiol /th’ÿ-ol, -ohl/ (thio alcohol; mercaptan) A compound of the type RSH, similar thiazole /th’ÿ-ă-zohl/ (C3H3NS) A colorless volatile liquid, a beterocyclic com- to an alcohol with the oxygen atom re- pound with a five-membered ring placed by sulfur. containing three carbon atoms, one nitrogen atom, and one sulfur atom. It resem- thionyl /th’ÿ-ŏ-năl/ Describing a com- bles PYRIDINE in its reactions. pound containing the group =SO. thin-layer chromatography A tech- thionyl chloride /th’ÿ-ŏ-năl/ See sulfur nique widely used for the analysis of mix- dichloride oxide. tures. Thin-layer chromatography employs a solid stationary phase, such as alumina or thiophene /th’ÿ-ŏ-feen/ (C4H4S) A color- silica gel, spread evenly as a thin layer on a less liquid that smells like benzene, a hete- glass plate. A base line is carefully rocyclic compound with a five-membered scratched near the bottom of the plate ring containing four carbon atoms and one using a needle, and a small sample of the sulfur atom. It occurs as an impurity in mixture is spotted onto the base line using commercial benzene and is used as a sol- a capillary tube. The plate is then stood up- vent and in organic syntheses. right in solvent, which rises up to the base line and beyond by capillary action. The thiosulfate /th’ÿ-oh-sul-fayt/ A salt con- components of the spot of the sample will taining the ion S O 2–. See sodium thiosul- dissolve in the solvent and tend to be car- 2 3 ried up the plate. However, some of the fate(IV). components will cling more readily to the solid phase than others and will not move thiourea /th’ÿ-oh-yû-ree-ă/ See thiocar- up the plate so rapidly. In this way, differ- bamide. ent fractions of the mixture eventually become separated. When the solvent has thixotropy /thiks-ot-rŏ-pee/ The change almost reached the top, the plate is re- of viscosity with movement. Fluids that un- moved and quickly dried. The plate is de- dergo a decrease in viscosity with increas- veloped to locate the positions of colorless ing velocity are said to be thixotropic. fractions by spraying with a suitable chem- Non-drip paint is an example of a ical or by exposure to ultraviolet radiation. thixotropic fluid.

273 thoria thoria /thor-ee-ă, thoh-ree-/ See thorium and considerable concentration must be dioxide. carried out before roasting. The metal itself is obtained by reduction using carbon, → thorium /thor-ee-ŭm, thoh-ree-/ A toxic SnO2 + C Sn + CO2 radioactive element of the actinoid series Tin is an expensive metal and several that is a soft ductile silvery metal. It has processes are used for recovering tin from several long-lived radioisotopes found in a scrap tin-plate. These may involve chlori- variety of minerals including monazite. nation (dry) to the volatile SnCl4, or elec- Thorium is used in magnesium alloys, in- trolytic methods using an alkaline candescent gas mantles, and nuclear fuel electrolyte: elements. – → 2– – Sn + 4OH Sn(OH)4 + 2e (anode) Symbol: Th; m.p. 1780°C; b.p. 4790°C Sn(OH) 2– → Sn2+ + 4OH– (cathode) ° 4 (approx.); r.d. 11.72 (20 C); p.n. 90; Sn2+ + 2e → Sn (cathode) r.a.m. 232.0381. Tin does not react directly with hydrogen but an unstable hydride, SnH4, can be thorium dioxide /dÿ-oks-ÿd, -id/ (thoria; prepared by reduction of SnCl4. The low ThO2) A white insoluble compound, used stability is due to the rather poor overlap of as a refractory, in gas mantles, and as a re- the diffuse orbitals of the tin atom with the placement for silica in some types of opti- small H-orbitals. Tin forms both tin(II) cal glass. oxide and tin(IV) oxide. Both are amphoteric, dissolving in acids to give tin(II) and three-ŏ-neen, -nin threonine / / See amino tin(IV) salts, and in bases to form stannites acids. and stannates, SnO + 4OH– → [SnO ]4– + 2H O thulium /thoo-lee-ŭm/ A soft malleable 3 2 stannite (relatively unstable) ductile silvery element of the lanthanoid se- SnO + 4OH– → [SnO ]4– + 2H O ries of metals. It occurs in association with 2 4 2 stannate other lanthanoids. The halides, SnX , may be prepared by Symbol: Tm; m.p. 1545°C; b.p. 2 dissolving tin metal in the hydrogen halide 1947°C; r.d. 9.321 (20°C); p.n. 69; r.a.m. or by the action of heat on SnO plus the hy- 168.93421. drogen halide. Tin(IV) halides may be prepared by direct reaction of halogen with thymidine /th’ÿ-mă-din, -deen/ The NU- the metal. Although tin(II) halides are ion- CLEOSIDE formed when thymine is linked to ized in solution their melting points are all D-ribose by a β-glycosidic bond. low suggesting considerable covalence in thymine /th’ÿ-min, -meen/ A nitrogenous all but the fluoride. The tin(IV) halides are base found in DNA. It has a PYRIMIDINE volatile and essentially covalent with slight ring structure. polarization of the bonds. Tin(II) compounds are readily oxidized to tin(IV) com- tin A white lustrous metal of low melting pounds and are therefore good reducing point; the fourth member of group 14 of agents for general laboratory use. the periodic table. Tin itself is the first dis- Tin has three crystalline modifications tinctly metallic element of the group even or allotropes, α-tin or ‘gray tin’ (diamond though it retains some amphoteric proper- structure), β-tin or ‘white tin’, and γ-tin; ties. Its electronic structure has outer s2p2 the latter two are metallic with close electrons ([Kr]4d105s25p2). The element is packed structures. Tin also has several iso- of low abundance in the Earth’s crust topes. It is used in a large number of alloys (0.004%) but is widely distributed, largely including Babbit metal, bell metal, Britan- as cassiterite (SnO2). The metal has been nia metal, bronze, gun metal, and pewter known since early bronze age civilizations as well as several special solders. when the ores used were relatively rich but Symbol: Sn; m.p. 232°C; b.p. 2270°C; currently worked ores are as low as 1–2% r.d. 7.31 (20°C); p.n. 50; r.a.m. 118.710.

274 titanium(IV) oxide tincal /tink-ăl/ A naturally occurring form tained by heating a mixture of tin filings, of borax. See disodium tetraborate decahy- sulfur, and ammonium chloride. Tin(IV) drate. sulfide is used as a pigment. tin(II) chloride (stannous chloride; SnCl2) titania /tÿ-tay-nee-ă, ti-/ See titanium(IV) A transparent solid made by dissolving tin oxide. in hydrochloric acid. Tin(II) chloride is a reducing agent, it combines with ammonia, titanic chloride /tÿ-tan-ik/ See and forms hydrates with water. It is used as titanium(IV) chloride. a mordant. titanic oxide See titanium(IV) oxide. tin(IV) chloride (stannic chloride; SnCl4) A colorless fuming liquid. Tin(IV) chloride titanium /tÿ-tay-nee-ŭm, ti-/ A silvery is soluble in organic solvents but is hy- transition metal that occurs in various ores drolyzed by water. It dissolves sulfur, as titanium(IV) oxide and also in combina- phosphorus, bromine, and iodine, and it tion with iron and oxygen. It is extracted dissolves in concentrated hydrochloric acid by conversion of titanium(IV) oxide to the 2– to give the anion SnCl6 . chloride, which is reduced to the metal by heating with sodium. Titanium is reactive tincture A solution in which alcohol at high temperatures. It is used in the aero- (ethanol) is the solvent (e.g., tincture of io- space industry as it is strong, resistant to dine). corrosion, and has a low density. It forms compounds with oxidation states +4, +3, tin(IV) hydride See stannane. and +2, the +4 state being the most stable. Symbol: Ti; m.p. 1660°C; b.p. 3287°C; tin(II) oxide (stannous oxide; SnO) A r.d. 4.54 (20°C); p.n. 22; r.a.m. 47.867. dark green or black solid. It can also be obtained in an unstable red form, which turns titanium(IV) chloride (titanic chloride; black on exposure to air. Tin(II) oxide can titanium tetrachloride; TiCl4) A volatile be made by precipitating the hydrated colorless liquid formed by heating tita- oxide from a solution containing tin(II) nium(IV) oxide with carbon in a stream of ions and dehydrating the product at dry chlorine at 700°C. The product is puri- 100°C. fied by fractional distillation. Titanium(IV) chloride fumes in moist air forming the tin(IV) oxide (stannic oxide; tin dioxide; oxychlorides of titanium. It undergoes hy- SnO2) A colorless crystalline solid, which drolysis in water but this can be prevented is usually discolored owing to the presence by the presence of excess hydrochloric of impurities. It exists as hexagonal or acid. Crystallization of such a solution rhombic crystals or in an amorphous form. gives crystals of the di- and pentahydrates. Tin(IV) oxide is insoluble in water. It is Titanium(IV) chloride is used in the prepa- used for polishing glass and metal. ration of pure titanium and as an intermediate in the production of titanium tin(II) sulfide (stannous sulfide; SnS) A compounds from minerals. gray solid that can be prepared from tin and sulfur. Above 265°C tin(II) sulfide titanium dioxide /dÿ-oks-ÿd/ See tita- slowly turns into tin(IV) sulfide and tin: nium(IV) oxide. → 2SnS(s) SnS2(s) + Sn(s) titanium(IV) oxide (titanic oxide; tita- tin(IV) sulfide (stannic sulfide; SnS2) A nium dioxide; TiO2) A white ionic solid yellowish solid that can be precipitated by that occurs naturally in three crystalline reacting hydrogen sulfide with a solution forms: rutile (tetragonal), brookite (or- of a soluble tin(IV) salt. A crystalline form thorhombic), and anatase (tetragonal). It sometimes known as mosaic gold is ob- reacts slowly with acids and is attacked by

275 titanium tetrachloride the halogens at high temperatures. On topaz A hydrous aluminosilicate mineral heating it decomposes to give titanium(III) containing some fluoride ions, used for oxide and oxygen. Titanium(IV) oxide is making refractories, glasses, and glazes. A amphoteric; it is used as a white pigment. clear pale yellow or brown form is used as With hot concentrated sulfuric acid, it a gemstone. forms titanyl sulfate, TiOSO4. When fused with alkalis, it forms titanates. torr A unit of pressure equal to a pressure of 101 325/760 pascals (133.322 Pa). One titanium tetrachloride /tet-ră-klor-ÿd, torr is equal to one mmHg. The unit is -id, -kloh-rÿd, -rid/ See titanium(IV) chlo- named for the Italian physicist Evangelista ride. Toricelli (1608–47). titrant /tÿ-trănt/ See titration. tracer An ISOTOPE of an element used to investigate chemical reactions or physical titration /tÿ-tray-shŏn/ A procedure in processes (e.g. diffusion). VOLUMETRIC ANALYSIS in which a solution of known concentration (called the titrant) trans- Designating an isomer with groups is added to a solution of unknown concen- that are on opposite sides of a bond or tration from a buret until the equivalence structure. See isomerism. point or end point of the titration is reached. transactinide elements /tran-sak-tă-nÿd, -zak-, -nid/ Those elements following 103 TNT See trinitrotoluene. Lw (i.e. following the actinide series). To date, element 104 (rutherfordium) through to element 112 have been synthe- Tollen’s reagent /tol-ĕn/ A solution of sized; so far, elements 110, 111, and 112 the complex ion Ag(NH ) + produced by 3 2 are unnamed. All are unstable and have precipitation of silver oxide from silver ni- very short half-lives. There is speculation trate with a few drops of sodium hydrox- that islands of stable nuclei with very high ide solution, and subsequent dissolution of mass numbers exist since theoretical calcu- the silver oxide in aqueous ammonia. Tol- lations predict unusual stability for ele- len’s reagent is used in the SILVER-MIRROR ments 114 and 184. TEST for aldehydes, where the Ag+ ion is reduced to silver metal. It is also a test for trans-fat See hardening. alkynes with a triple bond in the 1-position. A yellow precipitate of silver carbide transient species A short-lived interme- is formed in this case. diate in a chemical reaction. RCCH + Ag+ → RCC–Ag+ + H+ The reagent is named for Bernhard Tol- transition elements /tran-zish-ŏn/ A class lens (1841–1918). of elements occurring in the periodic table in four series: from scandium to zinc; from toluene /tol-yoo-een/ See methylbenzene. yttrium to cadmium; from lanthanum to mercury; and from actinium to element toluidine /tŏ-loo-ă-deen, -din/ (methylani- 112. The transition elements are all metals. line; aminotoluene; CH3C6H4NH2) An They owe their properties to the presence aromatic amine used in making dyestuffs of d electrons in the atoms. In the first tran- and drugs. There are three isomers; the 1,2- sition series, calcium has the configuration (ortho-aminotoluene) and 1,3- (meta-) 3s23p64s2. The next element scandium has forms are liquids, the 1,4- (para-) isomer is 3s23p63d14s2, and the series is formed by a solid. filling the d levels up to zinc at 3d104s2. The other transition series occur by filling of tonne /tun/ Symbol: t A unit of mass equal the 4d, 5d, and 6d levels. Often the ele- to 103 kilograms (i.e. one megagram). ments scandium, yttrium, and lanthanum

276 trichloroacetic acid are considered with the lanthanoids rather trolyte, the transport number of an ion is than the transition elements, and zinc, cad- the fraction of the total charge carried by mium, and mercury are also treated as a that type of ion in conduction. separate group. Transition elements have certain characteristic properties resulting transuranic elements /trans-yû-ran-ik, from the existence of d levels: tranz-/ Those elements of the actinoid se- 1. They have variable valences – i.e. they ries that have higher atomic numbers than can form compounds with the metal in uranium. The transuranic elements are different oxidation states (Fe2+ and Fe3+, formed by adding neutrons to the lower etc.). actinoids by high-energy bombardment 2. They form a vast number of inorganic and they generally have such short half- complexes, in which coordinate bonds lives that macroscopic isolation is impossi- are formed to the metal atom or ion. ble. Neptunium and plutonium are formed 3. Compounds of transition elements are in trace quantities by natural neutron bom- often colored. bardment from spontaneous fission of See also d-block elements; lanthanoids; 235U. metals; transactinide elements; zinc group. triaminotriazine /trÿ-am-ă-noh-trÿ-ă- transition state (activated complex) Sym- zeen/ See melamine. bol: ‡ A short-lived high-energy molecule, radical, or ion formed during a reaction be- triammonium phosphate /trÿ-ă-moh- tween molecules possessing the necessary nee-ŭm/ See ammonium phosphate. activation energy. The transition state decomposes at a definite rate to yield either triatomic /trÿ-ă-tom-ik/ Denoting a mol- the reactants again or the final products. ecule, radical, or ion consisting of three The transition state can be considered to be atoms. For example, O and H O are tri- at the top of the energy profile. 3 2 atomic molecules. For the reaction, X + YZ = X…Y…Z‡ → XY+ Z triazine /trÿ-ă-zeen, -zin/ (C H N ) A het- the sequence of events is as follows. X ap- 3 3 3 erocyclic organic compound with a six- proaches YZ and when it is close enough the electrons are rearranged producing a membered ring containing three carbon weakening of the bond between Y and Z. atoms and three nitogen atoms. There are A partial bond is now formed between X three isomers, used as dyestuffs and herbi- and Y producing the transition state. De- cides. See also melamine. pending on the experimental conditions, the transition state either breaks down to triazole /trÿ-ă-zohl/ (C2H3N3) A hetero- form the products or reverts back to the re- cyclic organic compound with a five-mem- actants. bered ring containing two carbon atoms and three nitrogen atoms. There are two transition temperature A temperature at isomers. which some definite physical change occurs in a substance. Examples of such tran- tribasic acid /trÿ-bay-sik/ An ACID with sitions are change of state, change of three replaceable hydrogen atoms (such as crystal structure, and change of magnetic phosphoric(V) acid, H3PO4). behavior. tribromomethane /trÿ-broh-moh-meth- transmutation /trans-myoo-tay-shŏn, ayn/ (bromoform; CHBr3) A colorless liq- tranz-/ A change of one element into an- uid compound. See haloform. other by radioactive decay or by bombardment of the nuclei with particles. trichloroacetic acid /trÿ-klor-oh-ă-see- tik, -set-ik, -kloh-roh-/ See chloroethanoic transport number Symbol: t In an elec- acid.

277 trichloroethanal

– – → trichloroethanal /trÿ-klor-oh-eth-ă-nal, CH3CHO + 3I + 4OH CHI3 + – -kloh-roh-/ (chloral; CCl3CHO) A color- HCOO + 3H2O less liquid aldehyde made by chlorinating The reaction also occurs with all ketones of ethanal. It was used to make the insecticide general formula CH3COR (R is an alkyl DDT. It can be hydrolyzed to give 2,2,2- group) and with secondary alcohols trichloroethanediol (chloral hydrate, CH3CH(OH)R. Iodoform is used as a test CCl3CH(OH)2). Most compounds with for such reactions (the iodoform reaction). two –OH groups on the same carbon atom are unstable. However, in this case the ef- triiron tetroxide /trÿ-ÿ-ern tet-roks-ÿd/ fect of the three chlorine atoms stabilizes (ferrosoferric oxide; magnetic iron oxide; the compound. It is used as a sedative. Fe3O4) A black solid prepared by passing either steam or carbon dioxide over red- 2,2,2-trichloroethanediol /trÿ-klor-oh- hot iron. It may also be prepared by pass- eth-ayn-dÿ-ol, -ohk, -kloh-roh-/ See ing steam over heated iron(II) sulfide. trichloroethanal. Triiron tetroxide occurs in nature as the mineral magnetite. It is insoluble in water trichloroethanoic acid /trÿ-klor-oh-eth- but will dissolve in acids to give a mixture ă-noh-ik, -kloh-roh-/ See chloroethanoic of iron(II) and iron(III) salts in the ratio acid. 1:2. Generally it is chemically unreactive; it is, however, a fairly good conductor of trichloromethane /trÿ-klor-oh-meth-ayn, electricity. -kloh-roh-/ (chloroform; CHCl ) A color- 3 trimer /trÿ-mer/ A molecule (or com- less volatile liquid formerly used as an pound) formed by addition of three identi- anesthetic. Now its main use is as a solvent cal molecules. See ethanal; methanal. and raw material for making other chlorinated compounds. Trichloromethane is trimethylaluminum /trÿ-meth-ăl-ă-loo- made by reacting ethanal, ethanol, or mă-nŭm/ (aluminum trimethyl; (CH3)3Al) propanone with chlorinated lime. A colorless liquid produced by the sodium reduction of dimethyl aluminum chloride. triclinic crystal /trÿ-klin-ik/ See crystal It ignites spontaneously on contact with air system. and reacts violently with water, acids, halogens, alcohols, and amines. Aluminum triglyceride /trÿ-gliss-ĕ-rÿd/ A GLYCERIDE alkyls are used in the Ziegler process for in which esters are formed with all three the manufacture of high-density poly- –OH groups of glycerol. ethene. trigonal bipyramid /trig-ŏ-năl bÿ-pi-ră- trimolecular /trÿ-mŏ-lek-yŭ-ler/ Describ- mid/ See complex. ing a reaction or step that involves three molecules interacting simultaneously with trigonal crystal See crystal system. the formation of a product. For example, the final step in reaction between hydrogen trihydrate /trÿ-hÿ-drayt/ A crystalline hy- peroxide and acidified potassium iodide is drated compound that contains three mol- trimolecular: + – → ecules of water of crystallization per HOI + H + I I2 + H2O molecule of compound. It is uncommon for reactions to take place involving trimolecular steps. The ox- trihydric alcohol /trÿ-hÿ-drik/ See triol. idation of nitrogen(II) oxide to nitrogen(IV) oxide, → triiodomethane /trÿ-ÿ-ŏ-doh-meth-ayn/ 2NO + O2 2NO2 (iodoform; CHI3) A yellow crystalline is often classified as a trimolecular reaction compound made by warming ethanal with but many believe it to involve two bimol- an alkaline solution of an iodide: ecular reactions.

278 tungsten carbide trinitroglycerine /trÿ-nÿ-troh-gliss-ĕ-rin, owing to salt hydrolysis. Trisodium phos- -reen/ See nitroglycerine. phate is used as a water softener. trinitrophenol /trÿ-nÿ-troh-fee-nol, -nohl/ triterpene See terpene. See picric acid. tritiated compound A compound in trinitrotoluene /trÿ-nÿ-troh-tol-yoo-een/ which one or more 1H atoms have been re- 3 (TNT; CH3C6H2(NO2)3) A yellow crys- placed by tritium ( H) atoms. talline solid. It is a highly unstable substance, used as an explosive. The tritium /trit-ee-ŭm, trish-/ Symbol: T, 3H compound is made by nitrating methylben- A radioactive isotope of hydrogen of mass zene and the nitro groups are in the 2, 4, number 3. The nucleus contains 1 proton and 6 positions. and 2 neutrons. Tritium decays with emission of low-energy beta radiation to give triol /trÿ-ol, -ohl/ (trihydric alcohol) An 3He. The half-life is 12.3 years. It is useful alcohol that has three hydroxyl groups as a tracer in studies of chemical reactions. (-OH) per molecule of compound. Compounds in which 3H atoms replace the usual 1H atoms are said to be tritiated. A triose /trÿ-ohs/ A SUGAR that contains positive tritium ion, T+, is a triton. three carbon atoms. triton /trÿ-tŏn/ See tritium. trioxoboric(III) acid /trÿ-oks-ŏ-bô-rik/ See boric acid. trivalent /trÿ-vay-lĕnt, triv-ă-/ (tervalent) Having a valence of three. trioxosulfuric(IV) acid / trÿ-oks-oh- sul- fyoor-ik / See sulfurous acid. tropylium ion /trŏ-pil-ee-ŭm/ The posi- + tive ion C7H7 , having a symmetrical trioxygen /trÿ-oks-ă-jĕn/ See ozone. seven-membered ring of carbon atoms. The tropylium ion ring shows non-ben- triple bond A covalent bond formed be- zenoid aromatic properties. tween two atoms in which three pairs of electrons contribute to the bond. One pair tryptophan /trip-tŏ-fan/ See amino acids. forms a sigma bond (equivalent to a single bond) and two pairs give rise to two pi tungsten /tung-stĕn/ A transition metal bonds. It is conventionally represented as occurring naturally in wolframite ≡ three lines, thus H–C C–H. See multiple ((Fe,Mn)WO4) and scheelite (CaWO4). It bond. was formerly called wolfram. It is used as the filaments in electric lamps and in vari- triple point The only point at which the ous alloys. gas, solid, and liquid phases of a substance Symbol: W; m.p. 3410 ± 20°C; b.p. can coexist in equilibrium. The triple point 5650°C; r.d. 19.3 (20°C); p.n. 74; r.a.m. of water (273.16 K at 101 325 Pa) is used 183.84. to define the kelvin. tungsten carbide Either of two carbides trisodium phosphate(V) /trÿ-soh-dee- (W2C and WC) produced by heating pow- ŭm/ (sodium orthophosphate; Na3PO4) A dered tungsten with carbon. The carbides white solid prepared by adding sodium hy- are extremely hard and are used in industry droxide to disodium hydrogenphosphate. to make cutting tools or as an abrasive. On evaporation white hexagonal crystals WC has a very high melting point ° of the dodecahydrate (Na3PO4.12H2O) (2770 C) and will conduct electricity. W2C may be obtained. These crystals do not ef- also has a very high melting point floresce or deliquesce. They dissolve read- (2780°C) but is a less efficient conductor of ily in water to produce alkaline solutions electricity. It is very resistant to chemical

279 turpentine attack and behaves in a manner very simi- vent in paints, polishes, and varnishes. See lar to that of tungsten. It is strongly at- resin. tacked by chlorine to give tungsten hexachloride, WCl6. turquoise /ter-koiz, -kwoiz/ A naturally occurring hydrated copper aluminum turpentine /ter-pĕn-tÿn/ (pine-cone oil) A yellow viscous resin obtained from conifer- phosphate, used as a green-blue gemstone. ous trees. It can be distilled to produce turpentine oil (also known simply as tyrosine /tÿ-rŏ-seen, -sin, ti-/ See amino turpentine), used in medicine and as a sol- acids.

280 U

→ ultracentrifuge /ul-tră-sen-tră-fyooj/ A CH3CH2Cl C2H4 + HCl high-speed centrifuge used for separating out very small particles. The sedimentation unit A reference value of a quantity used rate depends on the particle size, and the to express other values of the same quan- ultracentrifuge can be used to measure the tity. See also SI units. mass of colloidal particles and large molecules (e.g. proteins). unit cell The smallest group of atoms, ions, or molecules that, when repeated at ultrahigh vacuum See vacuum. regular intervals in three dimensions, will produce the lattice of a crystal system. ultramarine /ul-tră-mă-reen/ See lazurite. There are seven basic types of unit cells, which result in the seven crystal systems. ultraviolet /ul-tră-vÿ-ŏ-lĕt/ (UV) A form of ELECTROMAGNETIC RADIATION, shorter in unit processes (chemical conversions) wavelength than visible light. Ultraviolet The recognized steps used in chemical wavelengths range between about 1 nm processes, e.g. alkylation, distillation, hy- and 400 nm. Ordinary glasses are not drogenation, pyrolysis, nitration, etc. In- transparent to these waves; quartz is a dustrial processing and the economics, much more effective material for making design, and use of the equipment are based lenses and prisms for use with ultraviolet. on these unit processes rather than consid- Like light, ultraviolet radiation is produced eration of each reaction separately. by electronic transitions between the outer energy levels of atoms. However, having a univalent /yoo-nă-vay-lĕnt, yoo-niv-ă-/ higher frequency, ultraviolet photons carry (monovalent) Having a valence of one. more energy than those of light and can in- duce photolysis of compounds. universal indicator (multiple-range indicator) A mixture of indicator dyestuffs unimolecular /yoo-nă-mŏ-lek-yŭ-ler/ De- that shows a gradual change in color over scribing a reaction (or step) in which only a wide pH range. A typical formulation one molecule is involved. For example, ra- contains methyl orange, methyl red, bro- dioactive decay is a unimolecular reaction: mothymol blue, and phenolphthalein and Ra → Rn + α changes through a red, orange, yellow, Only one atom is involved in each disinte- green, blue, and violet sequence between gration. pH 3 and pH 10. Several commercial In a unimolecular chemical reaction, preparations are available as both solu- the molecule acquires the necessary energy tions and test papers. to become activated and then decomposes. The majority of reactions involve only uni- unnil- A prefix used in the names of new or bimolecular steps. The following reac- chemical elements. Synthetic elements with tions are all unimolecular: high proton numbers were given tempo- → N2O4 2NO2 rary names based on the proton number, → PCl5 PCl3 + Cl2 pending official agreement on the actual 281 unsaturated compound name to be used. These names were formed unsaturated solution See saturated solu- from the word elements in the next table. tion.

unsaturated vapor See saturated vapor. Element Number Symbol nil 0 n UPVC Unplasticized PVC; a hard-wear- un 1 u ing form of PVC used in building work bi 2 b (e.g. for window frames). tri 3 t quad 4 q uracil /yoor-ă-săl/ A nitrogenous base that pent 5 p is found in RNA, replacing the thymine of hex 6 h DNA. It has a pyrimidine ring structure. sept 7 s oct 8 0 uraninite /yoor-ă-nÿt/ See pitchblende.

uranium /yû-ray-nee-ŭm/ A toxic ra- The suffix -ium was also used (because the dioactive silvery element of the actinoid se- elements were metals). So element 104, for ries of metals. Its three naturally occurring example, had the temporary systematic radioisotopes, 238U (99.283% in abun- name unnilquadium (un + nil + quad + dance), 235U (0.711%), and 234U ium). The names for elements using this (0.005%), are found in numerous minerals system are shown in the table below. including the uranium oxides pitchblende, uraninite, and carnotite. The readily fis- unsaturated compound An organic sionable 235U is a major nuclear fuel and compound that contains at least one dou- nuclear explosive, while 238U is a source of ble or triple bond between two of its car- fissionable 239Pu. bon atoms. The multiple bond is relatively Symbol: U; m.p. 1132.5°C; b.p. weak; consequently unsaturated com- 3745°C; r.d. 18.95 (20°C); p.n. 92; r.a.m. pounds readily undergo addition reactions 238.0289. to form single bonds. Compare saturated compound. uranium hexafluoride /heks-ă-floo-ŏ-

P.N. Temporary name Symbol Name Symbol

101 unnilunium Unu mendelevium Md 102 unnilbium Unb nobelium No 103 unniltrium Unt lawrencium Lr 104 unnilquadium Unq rutherfordium Rf 105 unnilpentium Unq dubnium Db 106 unnilhexium Unh seaborgium Sg 107 unnilseptium Uns bohrium Bh 108 unniloctium Uno hassium Hs 109 unnilennium Une meitnerium Mt 110 ununnilium Uun darmstadtium Ds 111 unununium Uuu roentgenium Rg 112 ununbium Uub unnamed 113 ununtrium Uut unnamed 114 ununquadium Uuq unnamed 115 ununpentium Uup unnamed 116 ununhexium Uuh unnamed

282 UV rÿd/ (UF6) A crystalline volatile com- uranyl /yoor-ă-năl/ The inorganic radical 2+ pound, used in separating uranium iso- UO2 , as in uranyl nitrate UO2(NO3)2. topes by differences in the rates of gas diffusion. urea /yû-ree-ă/ (carbamide; CO(NH2)2) A white crystalline compound made from uranium–lead dating A technique for ammonia and carbon dioxide. It is used in dating certain rocks depending on the the manufacture of urea–formaldehyde decay of the radioisotope 238U to 206Pb (methanal) resins. Urea is the end product (half-life 4.5 × 109 years) or of 235U to of metabolism in many animals and is pre- 207Pb (half-life 7.1 × 108 years). The decay sent in urine. of 238U releases alpha particles and an estimate of the age of the rock can be made by urethane /yoor-ĕ-thayn/ (ethyl carbamate; measuring the amount of helium present. CO(NH2)OC2H5) A poisonous flammable Another method is to measure the amount organic compound, used in medicine, as a of radioactive lead present to the amount solvent, and as an intermediate in the man- of nonradioactive lead. See also radioactive ufacture of polyurethane resins. dating. uric acid /yoor-ik/ A nitrogen compound uranium(IV) oxide (uranium dioxide; produced from purines. In certain animals urania; UO2) An extremely poisonous ra- (e.g. birds and reptiles), it is the main ex- dioactive black crystalline solid. It occurs cretory product resulting from breakdown in pitchblende (uraninite) and is used in ce- of amino acids. In humans, uric acid crys- ramics, photographic chemicals, pigments, tals in the joints are the cause of gout. and as a nuclear fuel. uridine /yoor-ă-din, -deen/ The nucleoside uranium(VI) oxide (uranium trioxide; formed when uracil is linked to D-ribose by β UO3) An extremely poisonous radioactive a -glycosidic bond. orange solid, used as a pigment in ceramics and in uranium refining. UV See ultraviolet.

283 V

vacancy See defect. ple, in Al2O3 for the two aluminum atoms (valence 3) the product is 6 and for the vacuum (pl. vacuums or vacua) A space three oxygen atoms (valence 2) the product containing gas below atmospheric pres- is also 6. sure. A perfect vacuum contains no matter The valence of an element is generally at all, but for practical purposes soft (low) equal to either the number of valence elec- vacuum is usually defined as down to trons or eight minus the number of valence about 10–2 pascal, and hard (high) vacuum electrons. Transition metal ions display as below this. Ultrahigh vacuum is lower variable valence. than 10–7 pascal. valence band The highest ENERGY LEVEL vacuum distillation The distillation of in a SEMICONDUCTOR or nonconductor that liquids under a reduced pressure, so that can be occupied by electrons. the boiling point is lowered. Vacuum distillation is a common laboratory technique valence-bond theory A technique for for purifying or separating compounds calculating the electronic structure of mol- that would decompose at their ‘normal’ ecules. In valence-bond theory the starting boiling point. point is to consider the atoms in a molecule and the ways in which valence electrons in vacuum flask See Dewar flask. the atoms can pair up in chemical bonds. Each way of pairing up the electrons is valence /vay-lĕns/ (valency) The combin- called a valence bond structure. The over- ing power of an element or radical, equal all structure for the molecule is determined to the number of hydrogen atoms that will by a linear combination of the wavefunc- combine with or displace one atom of the tions for the valence-bond structures. See element. For simple covalent molecules the resonance. valence is obtained directly, for example C in CH4 is tetravalent; N in NH3 is trivalent. valence electron An outer electron in an For ions the valence is regarded as equiva- atom that can participate in forming chem- lent to the magnitude of the charge; for ex- ical bonds. 2+ 2– ample Ca is divalent, CO3 is a divalent radical. The rare gases are zero-valent be- valency /vay-lĕns/ See valence. cause they do not form compounds under normal conditions. As the valence for valeric acid /vă-le-rik, -leer-ik/ See pen- many elements is constant, the valence of tanoic acid. some elements can be deduced without reference to compounds formed with hydro- valine /val-een, -in/ See amino acids. gen. Thus, as the valence of chlorine in HCl is 1, the valence of aluminum in AlCl3 is 3; vanadium /vă-nay-dee-ŭm/ A silvery tran- as oxygen is divalent (H2O) silicon in SiO2 sition element occurring in complex ores in is tetravalent. The product of the valence small quantities. It is used in alloy steels. and the number of atoms of each element Vanadium forms compounds with oxida- in a compound must be equal. For exam- tion states +5, +4, +3, and +2.

284 vapor pressure

It forms colored ions. the number of entities present. For exam- Symbol: V; m.p. 1890°C; b.p. 3380°C; ple, if n moles of a compound are dissolved r.d. 6.1 (20°C); p.n. 23; r.a.m. 50.94. and dissociation into ions occurs, then the number of particles present will be in. Os- vanadium(V) oxide (vanadium pentox- motic pressure (π), for instance, will be ide; V2O5) An oxide of vanadium exten- given by the equation sively used as a catalyst in oxidation πV = inRT processes, as in the contact process. The factor is named for the Dutch theoretical chemist Jacobus Henricus Van’t van der Waals equation /van-der-wawlz/ Hoff (1852–1911). An equation of state for real gases. For n moles of gas the equation is van’t Hoff isochore The equation: (p + n2a/V2)(V – nb) = nRT ∆ 2 d(logeK)/dT = H/RT where p is the pressure, V the volume, and showing how the equilibrium constant, K, T the thermodynamic temperature. a and b of a reaction varies with thermodynamic are constants for a given substance and R is temperature, T. ∆H is the enthalpy of reac- the gas constant. The equation gives a bet- tion and R is the gas constant. ter description of the behavior of real gases than the perfect gas equation (pV = nRT). vapor A gas formed by the vaporization The equation contains two corrections: of a solid or liquid. Some particles near the b is a correction for the non-negligible size 2 surface of a liquid acquire sufficient energy of the molecules; a/V corrects for the fact in collisions with other particles to escape that there are attractive forces between the from the liquid and enter the vapor; some molecules, thus slightly reducing the pres- particles in the vapor lose energy in colli- sure from that of an ideal gas. The equa- sions and re-enter the liquid. At a given tion is named for the Dutch physicist temperature an equilibrium is established, Johannes Diderik van der Waals which determines the vapor pressure of the (1837–1923). See also gas laws; kinetic liquid at that temperature. theory. The ratio of the mass of a van der Waals force An intermolecular vapor density force of attraction, considerably weaker certain volume of a vapor to the mass of an than chemical bonds and arising from equal volume of hydrogen (measured at the weak electrostatic interactions between same temperature and pressure). Determi- molecules (the energies are often less than nation of vapor densities is one method of 1 J mol–1). finding the relative molecular mass of a The van der Waals interaction contains compound (equal to twice the vapor den- contributions from three effects; perma- sity). Victor Meyer’s method, Dumas’ nent dipole–dipole interactions found for method, or Hofmann’s method can be any polar molecule; dipole–induced dipole used. interactions, where one dipole causes a slight charge separation in bonds that have vaporization The process by which a liq- a high polarizability; and dispersion forces, uid or solid is converted into a gas or vapor which result from temporary polarity aris- by heat. Unlike boiling, which occurs at a ing from an asymmetrical distribution of fixed temperature, vaporization can occur electrons around the nucleus. Even atoms at any temperature. Its rate increases as the of the rare gases exhibit dispersion forces. temperature rises. van’t Hoff factor /vant-hoff/ Symbol: i vapor pressure The pressure exerted by a The ratio of the number of particles present vapor. The saturated vapor pressure is the in a solution to the number of undissoci- pressure of a vapor in equilibrium with its ated molecules added. It is used in studies liquid or solid. It depends on the nature of of colligative properties, which depend on the liquid or solid and the temperature.

285 vat dyes vat dyes A class of insoluble dyes applied Meyer (1848–97). See also Dumas’ by first reducing them to derivatives that method; Hofmann’s method. are soluble in dilute alkali. In this condition they have a great attraction for certain vinegar A dilute solution (about 4% by fibers, such as cotton. The solution is ap- volume) of ETHANOIC ACID (acetic acid), plied to the material and the insoluble dye often with added coloring and flavoring is regenerated in the fibers by atmospheric such as caramel. Natural vinegar is pro- oxidation. Indigo and indanthrene are ex- duced by the bacterial fermentation of amples of vat dyes. cider or wine; it can also be made synthetically. verdigris /ver-di-grees, -gris, -gree/ Any of various greenish basic salts of copper. True vinylation /vÿ-nă-lay-shŏn/ A catalytic re- verdigris is basic copper acetate, a green or action in which a compound adds across blue solid of variable composition used as the triple bond of ethyne (acetylene) to a paint pigment. The term is often applied form an ethenyl (vinyl) compound. For ex- to green patinas formed on metallic cop- ample, an alcohol can add as follows: ≡ → per. Copper cooking vessels can form a ROH + HC CH RHC=CH(OH) coating of basic copper carbonate, vinyl benzene /vÿ-năl/ See phenylethene. CuCO3.Cu(OH)2. The verdigris formed on copper roofs and domes is usually basic vinyl chloride See chloroethene. copper sulfate, CuSO4.3Cu(OH)2.H2O, while basic copper chloride, vinyl group The group CH2:CH–. CuCl2.Cu(OH)2, may form in regions near the sea. viscose rayon /viss-kohs/ See rayon. vermilion See mercury(II) sulfide. viscosity /vis-koss-ă-tee/ Symbol: η The resistance to flow of a fluid. vesicant /ves-ă-kănt/ A substance that causes blistering of the skin. Mustard gas is visible radiation See light. an example. vitreous /vit-ree-ŭs/ Resembling glass, or vis-ă-năl vicinal positions / / Positions in a having the structure of a glass. molecule at adjacent atoms. For example, in 1,2-dichloroethane the chlorine atoms volatile Easily converted into a vapor. are in vicinal positions, and this compound can thus be named vic-dichloroethane. volt Symbol: V The SI unit of electrical potential, potential difference, and e.m.f., Victor Meyer’s method /vik-ter mÿ-erz/ defined as the potential difference between A method for determining vapor densities two points in a circuit between which a in which a given weight of sample is va- constant current of one ampere flows when porized and the volume of air displaced by the power dissipated is one watt. 1 V = 1 J it is measured. In practice, a bulb in a heat- C–1. The unit is named for the Italian physi- ing bath is connected via a fairly long tube cist Count Alessandro Volta (1745–1827). to a water-bath gas-collection arrangement. The system is brought to equilibrium voltaic cell /vol-tay-ik/ See cell. and the sample is then added (without opening the apparatus to the atmosphere). volume strength See hydrogen peroxide. As the air displaced by gas is collected over water a correction for the vapor pressure of volumetric analysis /vol-yŭ-met-rik/ One water is necessary and the method may fail of the classical wet methods of quantitative if the vapor is soluble in water. The method analysis. It involves measuring the volume is named for the German chemist Victor of a solution of accurately known concen-

286 vulcanization tration that is required to react with a so- mined by minimizing the Coulomb repul- lution of the substance being determined. sion between pairs and the repulsion be- The solution of known concentration (the tween pairs due to the Pauli exclusion standard solution) is added in small por- principle. Thus, for three pairs of electrons tions from a buret. The process is called a an equilateral triangle is favored and for titration and the equivalence point is called four pairs of electrons a tetrahedron is fa- the end point. End points are observed vored. The VSEPR theory has had consid- with the aid of indicators or by instrumen- erable success in predicting molecular tal methods, such as conduction or light shapes. See lone pair. absorption. Volumetric analysis can also be applied to gases. The gas is typically vulcanite /vul-kă-nÿt/ (ebonite) A hard held over mercury in a graduated tube, and black insulator made by vulcanizing rub- volume changes are measured on reaction or after absorption of components of a ber with a large amount of sulfur. mixture. vulcanization /vul-kă-ni-zay-shŏn/ A VSEPR (valence-shell electron-pair repul- process of improving the quality of rubber sion) A method of predicting the shape of (hardness and resistance to temperature molecules. In this theory one atom is taken changes) by heating it with sulfur (about to be the central atom and pairs of valence 150°C). Accelerators are used to speed up electrons are drawn round the central the reaction. Certain sulfur compounds atom. The shape of the molecule is deter- can also be used for vulcanization.

287 W

Wacker process /wak-er/ An industrial velop between the hydrogen atom and oxy- process for making ethanal (and other car- gen atoms in adjacent molecules, giving ice bonyl compounds). To produce ethanal, its tetrahedral crystalline structure with a ethene and air are bubbled through an acid density of 916.8 kg m–3 at STP. Different solution of palladium(II) chloride and cop- ice structures develop under higher pres- per(II) chloride (20–60°C and moderate sures. When ice melts to form liquid water, pressure): the tetrahedral structure breaks down, but 2+ → C2H4 + Pd + O2 CH3CHO + Pd + some hydrogen bonds continue to exist; 2H+ liquid water consists of groups of associ- The reaction involves an intermediate ated water molecules, (H2O)n, mixed with complex between palladium(II) ions and some monomers and some dimers. This ethene. The purpose of the copper(II) chlo- mixture of molecular species has a higher ride is to oxidize the palladium back to density than the open-structured crystals. Pd2+ ions: The maximum density of water, 999.97 kg Pd + 2Cu2+ → Pd2+ + 2Cu+ m–3, occurs at 3.98°C. This accounts for The copper(I) ions spontaneously oxidize the ability of ice to float on water and for to copper(II) ions in air. The process pro- the fact that water pipes burst on freezing. vides a cheap source of ethanal (and, by Although water is predominantly a co- oxidation, ethanoic acid) from the readily valent compound, a very small amount of ˆ + available ethene. ionic dissociation occurs (H2O H + OH–). In every liter of water at STP there is Walden inversion /wawl-dĕn/ A reaction approximately 10–7 mole of each ionic in which an optically active compound re- species. It is for this reason that, on the pH acts to give an optically active product in scale, a neutral solution has a value of 7. which the configuration has been inverted. As a polar liquid, water is the most This happens in the SN2 mechanism. The powerful solvent known. This is partly a inversion is named for the Russian–Ger- result of its high dielectric constant and man chemist Paul Walden (1863–1957). partly its ability to hydrate ions. This latter See nucleophilic substitution. property also accounts for the incorporation of water molecules into some ionic washing soda See sodium carbonate. crystals as water of crystallization. Water is decomposed by reactive metals water (H2O) A colorless liquid that (e.g. sodium) when cold and by less active freezes at 0°C and, at atmospheric pres- metals (e.g. iron) when steam is passed sure, boils at 100°C. In the gaseous state over the hot metal. It is also decomposed water consists of single H2O molecules. by electrolysis. Due to the presence of two lone pairs the atoms do not lie in a straight line, the angle water gas A mixture of carbon monoxide between the central oxygen atom and the and hydrogen produced when steam is two hydrogen atoms being 105°; the dis- passed over red-hot coke or made to com- tance between each hydrogen atom and the bine with hydrocarbons, e.g. → oxygen atom is 0.099 nm. When ice forms, C(s) + H2O(g) CO(g) + H2(g) → hydrogen bonds some 0.177 nm long de- CH4(g) + H2O(g) CO(g) + 3H2(g) 288 wet cell

The production of water gas using wavelength Symbol: λ The distance be- methane is an important step in the prepa- tween the ends of one complete cycle of a ration of hydrogen for ammonia synthesis. wave. Wavelength is related to the speed Compare producer gas. (c) and frequency (v) thus: c = vλ water glass See sodium silicate. wave mechanics See quantum theory. water of crystallization Water present in definite proportions in crystalline com- wave number Symbol: σ The reciprocal pounds. Compounds containing water of of the wavelength of a wave. It is the num- crystallization are called hydrates. Exam- ber of wave cycles in unit distance, and is ples are copper(II) sulfate pentahydrate often used in spectroscopy. The unit is the –1 –1 (CuSO4.5H2O) and sodium carbonate dec- meter (m ). The circular wave number ahydrate (Na2CO3.10H2O). The water can (symbol: k) is given by: be removed by heating. k = 2πσ When hydrated crystals are heated the water molecules may be lost in stages. For wax A soft amorphous water-repellant or- example, copper(II) sulfate pentahydrate ganic material. The term is particularly changes to the monohydrate (CuSO4.H2O) used for fatty-acid esters of monohydric al- at 100°C, and to the anhydrous salt cohols. ° (CuSO4) at 250 C. The water molecules in crystalline hydrates may be held by hydro- weak acid (or base) An acid or base that gen bonds (as in CuSO4.H2O) or, alterna- is not fully dissociated in solution. tively, may be coordinated to the metal ion as a complex aquo ion. weak base A base that is only partly or in- completely dissociated into its component water softening The removal from water ions in solution. of dissolved calcium, magnesium, and iron compounds, thus reducing the hardness of weber /vay-ber/ Symbol: Wb The SI unit the water. The compounds are potentially of magnetic flux, equal to the magnetic damaging because they can accumulate in flux that, linking a circuit of one turn, pro- pipes and boilers and they react with, and duces an e.m.f. of one volt when reduced to therefore waste, soap. Temporary hardness zero at uniform rate in one second. 1 Wb = can be removed by boiling the water. Per- 1 V s. The unit is named for the German manent hardness can be removed in a num- physicist Wilhelm Eduard Weber ber of ways: by distillation; by the addition (1804–91). of sodium carbonate, which causes dissolved calcium, for example, to precipitate Weston cadmium cell A standard cell out as calcium carbonate; and by the use of that produces a constant e.m.f. of 1.0186 ion-exchange products such as Permutit volts at 20°C. It consists of an H-shaped and Calgon. See also hardness (of water). glass vessel containing a negative cadmium-mercury amalgam electrode in one watt /wot/ Symbol: W The SI unit of leg and a positive mercury electrode in the power, defined as a power of one joule per other. The electrolyte – saturated cadmium second. 1 W = 1 J s–1. The unit is named for sulfate solution – fills the horizontal bar of the British instrument maker and inventor the vessel to connect the two electrodes. James Watt (1736–1819). The e.m.f. of the cell varies very little with temperature, being given by the equation E wavefunction /wayv-fung-shŏn/ See = 1.0186 – 0.000 037 (T – 293), where T is quantum theory; orbital. the thermodynamic temperature. waveguides /wayv-gÿdz/ See microwaves. wet cell A type of cell, such as a car bat-

289 white arsenic tery, in which the electrolyte is a liquid so- produced by evaporating NH4NCO (am- lution. See also Leclanché cell. monium cyanate). The experiment was important as it demonstrated that ‘organic’ white arsenic See arsenic(III) oxide. chemicals (i.e. ones produced in living organisms) could be made from inorganic white lead See lead(II) carbonate hydrox- starting materials. The synthesis is named ide. for the German chemist Friedrich Wöhler (1800–82). white phosphorus See phosphorus. wolfram /wûlf-răm/ A former alternative white spirit A liquid hydrocarbon resem- name for tungsten. bling kerosene obtained from petroleum, used as a solvent and in the manufacture of wood alcohol See methanol. paints and varnishes. Wood’s metal A fusible alloy containing Williamson’s continuous process A 50% bismuth, 25% lead, and 12.5% tin method of preparing simple ethers by de- and cadmium. Its low melting point (70°C) hydration of alcohols with concentrated leads to its use in fire-protection devices. sulfuric acid. The reaction is carried out at The alloy is named for the English scientist 140°C under reflux with an excess of the William Wood (1671–1730). alcohol: → 2ROH ROR + H2O work function See photoelectric effect. The concentrated sulfuric acid both catalyzes the reaction and displaces the equi- wrought iron A low-carbon steel ob- librium to the right. The product, ether, is tained by refining the iron produced in a termed ‘simple’, because the R groups are blast furnace. Wrought iron is processed identical. by heating and hammering to reduce the slag content and to ensure its even distrib- Williamson’s synthesis A method for ution. the preparation of mixed ethers by nucleophilic substitution. A haloalkane is re- Wurtz reaction /voorts/ A reaction for fluxed with an alcoholic solution of preparing alkanes by refluxing a sodium alkoxide (from sodium dissolved in haloalkane (RX) with sodium metal in dry alcohol): ether: R′Cl + RO–Na+ → R′OR + NaCl 2RX + 2Na → RR + 2NaX The product ether is termed ‘mixed’ if the The reaction involves the coupling of two alkyl groups R and R′ are different. This alkyl radicals. The Fittig reaction is a simi- synthesis can produce both simple and lar process for preparing alkyl-benzene hy- mixed ethers. The synthesis is named for drocarbons by using a mixture of halogen the British chemist Alexander William compounds. For example, to obtain Williamson (1824–1904). methylbenzene: → C6H5Cl + CH3Cl + 2Na C6H5CH3 + will-o’-the-wisp See ignis fatuus. 2NaCl In this mixed reaction phenylbenzene witherite /with-ĕ-rÿt/ A mineral form of (C6H5C6H5) and ethane (CH3CH3) are barium carbonate, BaCO3. also produced by side reactions. The Wurtz reaction is named for the French chemist Wöhler’s synthesis /voh-lerz/ A synthesis Charles Adolphe Wurtz (1817–84) and the of urea from inorganic compounds Fittig reaction is named for the German or- (Friedrich Wöhler, 1828). The urea was ganic chemist Rudolph Fittig (1835–1910).

290 X

xanthate /zan-thayt/ (-SCS(OR)) A salt or use in medicine and industry for investigat- ester of XANTHIC ACID (where R is an or- ing internal structures). It can be detected ganic group). Cellulose xanthate is used to with photographic emulsions and devices make RAYON. like the Geiger–Müller tube. X-ray photons result from electronic xanthene /zan-theen/ (CH2(C6H4)2O) A transitions between the inner energy levels yellow crystalline organic compound, used of atoms. When high-energy electrons are in making dyestuffs and fungicides. absorbed by matter, an x-ray line spectrum results. The structure depends on the sub- xanthic acid /zan-thik/ (HSCS(OR)) Any stance and is thus used in x-ray spec- of several unstable organic acids (where R troscopy. The line spectrum is always is an organic group), whose esters and salts formed in conjunction with a continuous have various industrial applications. See background spectrum. The minimum (cut- λ xanthate. off) wavelength 0 corresponds to the maximum x-ray energy, Wmax. This equals the xanthine /zan-theen, -th’ÿn/ (2,6-dioxy- maximum energy of electrons in the beam purine; C5H4N2O2) A poisonous colorless producing the x-rays. Wavelengths in the λ crystalline organic compound that occurs continuous spectrum above 0 are caused in blood, coffee beans, potatoes, and urine. by more gradual energy loss by the elec- It is used as a chemical intermediate. trons, in the process called bremsstrahlung (braking radiation). xanthone /zan-thohn/ (dibenzo-4-pyrone; CO(C6H4)2O) A colorless crystalline or- x-ray crystallography The study of the ganic compound found as a pigment in internal structure of crystals using the tech- gentians and other flowers. It is used as an nique of x-ray diffraction. insecticide and in making dyestuffs. x-ray diffraction A technique used to de- xenon /zen-on/ A colorless odorless termine crystal structure by directing x- monatomic element of the rare-gas group. rays at the crystals and examining the It occurs in trace amounts in air. Xenon is diffraction patterns produced. At certain used in electron tubes and strobe lighting. angles of incidence a series of spots are pro- Symbol: Xe; m.p. –111.9°C; b.p. duced on a photographic plate; these spots –107.1°C; d. 5.8971 (0°C) kg m–3; p.n. 54; are caused by interaction between the x- r.a.m. 131.29. rays and the planes of the atoms, ions, or molecules in the crystal lattice. The posi- x-radiation An energetic form of electro- tions of the spots are consistent with the magnetic radiation. The wavelength range Bragg equation nλ = 2dsinθ. is 10–11 m to 10–8 m. X-rays are normally produced by absorbing high-energy elec- x-rays See x-radiation. trons in matter. The radiation can pass through matter to some extent (hence its xylene /zÿ-leen/ See dimethylbenzene.

291 YZ

′ → ′ yellow phosphorus See phosphorus. ROR + 2HI H2O + RI + R I Analysis to identify the iodoalkanes yocto- Symbol: y A prefix denoting 10–24. gives information about the composition For example, 1 yoctometer (ym) = 10–24 of the original ether. meter (m). Zeise’s salt /zÿ-sĕz, tsÿ-/ A complex of yotta- Symbol: Y A prefix denoting 1024. platinum and ethane (ethylene) first syn- For example, 1 yottameter (Ym) = 1024 thesized by W. C. Zeise in 1827. It has the meter (m). formula PtCl3(CH2CH2) and was the first complex in which the metal ion coordi- ytterbium /i-ter-bee-ŭm/ A soft malleable nated to a pi-electron system rather than to silvery element having two allotropes and individual atoms. belonging to the lanthanoid series of metals. It occurs in association with other lan- zeolite /zee-ŏ-lÿt/ A member of a group of thanoids. Ytterbium has been used to hydrated aluminosilicate minerals, which improve the mechanical properties of steel. occur in nature and are also manufactured Symbol: Yb; m.p. 824°C; b.p. 1193°C; for their ion-exchange and selective-ab- r.d. 6.965 (20°C); p.n. 70; r.a.m. 173.04. sorption properties. They are used for water softening and for sugar refining. The yttrium /it-ree-ŭm/ A silvery metallic ele- zeolites have an open crystal structure and ment belonging to the second transition se- can be used as MOLECULAR SIEVES. See also ries. It is found in almost every lanthanoid ion exchange. mineral, particularly monazite. Yttrium is used in various alloys, in yttrium–alu- zepto- Symbol: z A prefix denoting 10–21. minum garnets used in the electronics in- For example, 1 zeptometer (zm) = 10–21 dustry and as gemstones, as a catalyst, and meter (m). in superconductors. A mixture of yttrium and europium oxides is widely used as the zero order Describing a chemical reaction red phosphor on television screens. in which the rate of reaction is independent Symbol: Y; m.p. 1522°C; b.p. 3338°C; of the concentration of a reactant; i.e. r.d. 4.469 (20°C); p.n. 39; r.a.m. rate = k[X]0 88.90585. The concentration of the reactant remains constant for a period of time al- Zeeman effect /zay-mahn/ The splitting though other reactants are being of atomic spectral lines by an external ap- consumed. The hydrolysis of 2-bromo-2- plied magnetic field. It was first reported methylpropane using aqueous alkali has a by the Dutch physicist Pieter Zeeman rate expression, (1865–1943) in 1896. rate = k[2-bromo-2-methylpropane] i.e. the reaction is zero order with respect Zeisel reaction /zÿ-sĕl/ The reaction of an to the concentration of the alkali (it does ether with excess concentrated hydroiodic not depend on the alkali concentration). acid. On refluxing, a mixture of iodoalka- The rate constant for a zero reaction has nes is formed: the units mol dm–3 s–1.

292 zinc group zero point energy The energy possessed amond structure is produced. Wurtzite by the atoms and molecules of a substance (another form of zinc sulfide) is similar but at absolute zero (0 K). belongs to the hexagonal crystal system. zetta- Symbol: Z A prefix denoting 1021. zinc-blende structure A form of crystal For example, 1 zettameter (Zm) = 1021 structure that consists of a zinc atom sur- meter (m). rounded by four sulfur atoms arranged tetrahedrally; each sulfur atom is similarly Ziegler process /zee-gler/ A method for surrounded by four atoms of zinc. Zinc sul- the manufacture of high-density poly- fide crystallizes in the cubic system. Cova- ethene using a catalyst of titanium(IV]] lent bonds of equal strength and length chloride and triethyl aluminum result in the formation of a giant molecular (Al(C2H5)3) under slight pressure. The structure. If the zinc and sulfur atoms are mechanism involves formation of titanium replaced by carbon atoms the diamond alkyls structure is produced. Wurtzite (another TiCl3(C2H5) form of zinc sulfide) is similar but belongs which coordinate the σ-orbitals of tita- to the hexagonal crystal system. nium with the π bond of ethene. The chain- length, and hence the density, of the zinc carbonate See calamine. polymer can be controlled. The process is named for the German chemist Karl zinc chloride (ZnCl2) A white crystalline Ziegler (1898–1973). solid prepared by the action of dry hydrogen chloride or chlorine on heated zinc. zinc A bluish-white transition metal oc- The anhydrous product undergoes subli- curring naturally as the sulfide (zinc mation. The hydrated salt may be prepared blende) and carbonate (smithsonite). It is by the addition of excess zinc to dilute hy- extracted by roasting the ore in air and drochloric acid and crystallization of the then reducing the oxide to the metal using solution. Hydrates with 4, 3, 5/2, 3/2, and carbon. Zinc is used to galvanize iron, in 1 molecule of water exist. Zinc chloride is alloys (e.g. brass), and in dry batteries. It extremely deliquescent and dissolves easily reacts with acids and alkalis but only cor- in water. It is used in dentistry, Leclanché rodes on the surface in air. Zinc ions are cells, as a flux, and as a dehydrating agent identified in solution by forming white pre- in organic reactions. cipitates with sodium hydroxide or ammonia solution, both precipitates being zinc group A group of metallic elements soluble in excess reagent. in the periodic table, consisting of zinc Symbol: Zn; m.p. 419.58°C; b.p. (Zn), cadmium (Cd), and mercury (Hg). 907°C; r.d. 7.133 (20°C); p.n. 30; r.a.m. The elements all occur at the ends of the 65.39. three transition series and all have outer d10s2 configurations; Zn [Ar]3d104s2, Cd zincate /zink-ayt/ A salt containing the ion [Kr]4d105s2, Hg[Xn]5d106s2. The elements 2– ZnO2 . all use only outer s-electrons in reaction and in combination with other elements zinc-blende (sphalerite) structure A unlike the coinage metals, which immedi- form of crystal structure that consists of a ately precede them. Thus all form diposi- zinc atom surrounded by four sulfur atoms tive ions, and oxidation states higher than arranged tetrahedrally; each sulfur atom is +2 are not known. In addition mercury similarly surrounded by four atoms of zinc. forms the mercurous ion, sometimes writ- Zinc sulfide crystallizes in the cubic sys- ten as Hg(I]], but actually the ion +Hg-Hg+. tem. Covalent bonds of equal strength and Although the elements fall naturally at the length result in the formation of a giant end of the transition series their properties molecular structure. If the zinc and sulfur are more like those of main-group elements atoms are replaced by carbon atoms the di- than of transition metals:

293 zincite

1. The melting points of the transition ele- bonate. On crystallization the hydrated ments are generally high whereas those salt is formed. The heptahydrate ° ° of the zinc group are low (Zn 419.5 C, (ZnSO4.7H2O) is formed below 30 C, the ° ° ° Cd 329.9 C, Hg –38.87 C). hexahydrate (ZnSO4.6H2O) above 30 C, 2. The zinc-group ions are diamagnetic and the monohydrate (ZnSO4.H2O) at and colorless whereas most transition el- 100°C; at 450°C the salt is anhydrous. ements have colored ions and many Zinc sulfate is extremely soluble in water. paramagnetic species. It is used in the textile industry. 3. The zinc group does not display the variable valence associated with transition zinc sulfide (ZnS) A compound that can metal ions. However the group does be prepared by direct combination of zinc have the transition-like property of and sulfur. Alternatively it can be prepared forming many complexes or coordina- as a white amorphous precipitate by bub- 2+ tion compounds, such as [Zn(NH3)4] bling hydrogen sulfide through an alkaline 2– and [Hg(CN]]4] . solution of a zinc salt or by the addition of Within the group, mercury is anom- ammonium sulfide to a soluble zinc salt so- 2+ alous because of the Hg2 ion mentioned lution. Zinc sulfide occurs naturally as the above and its general resistance to reac- mineral zinc blende. It dissolves in dilute tion. Zinc and cadmium are electropositive acids to yield hydrogen sulfide. Impure and will react with dilute acids to release zinc sulfide is phosphorescent. It is used as hydrogen whereas mercury will not. When a pigment and in the coatings on lumines- zinc and cadmium are heated in air they cent screens. burn to give the oxides, MO, which are stable to further strong heating. In contrast zircon /zer-kon/ See zirconium. mercury does not react readily with oxygen (slow reaction at the boiling point), and zirconium /zer-koh-nee-ŭm/ A hard lus- mercuric oxide, HgO, decomposes to the trous silvery transition element that occurs metal and oxygen on further heating. All in a gemstone, zircon (ZrSiO ). It is used in members of the group form dialkyls and di- 4 some strong alloy steels. aryls, R M. 2 Symbol: Zr; m.p. 1850°C; b.p. 4380°C; ° zincite /zink-ÿt/ (spartalite) A red-orange r.d. 6.506 (20 C); p.n. 40; r.a.m. 91.224. mineral form of ZINC OXIDE, ZnO, often containing also some manganese. It is an zwitterion /tsvit-er-ÿ-on, -ŏn, zwit-/ (am- important ore of zinc. pholyte ion) An ion that has both a positive and negative charge on the same zinc oxide (ZnO) A compound prepared species. Zwitterions occur when a mole- by the thermal decomposition of zinc ni- cule contains both a basic group and an trate or carbonate; it is a white powder acidic group; formation of the ion can be when cold, yellow when hot. Zinc oxide is regarded as an internal acid-base reaction. an amphoteric oxide, almost insoluble in For example, amino-ethanoic acid water, but dissolves readily in both acids (glycine) has the formula and alkalis. If mixed with powdered car- H2+N.CH2.COOH. Under neutral condi- bon and heated to red heat, it is reduced to tions it exists as the zwitterion – the metal. Zinc oxide is used in the paint H3N.CH2.COO , which can be formed by and ceramic industries. Medically it is used transfer of a proton from the carboxyl in zinc ointment. group to the amine group. At low pH (acidic conditions) the ion + zinc sulfate (ZnSO4) A white crystalline H3N.CH2.COOH is formed; at high pH – solid prepared by the action of dilute sulfu- (basic conditions) H2N.CH2.COO is ric acid on either zinc oxide or zinc car- formed. See also amino acid.

294 APPENDIXES

Appendix I Carboxylic Acids

In the examples below, the systematic name is given first, followed by the trivial (common) name.

Simple saturated monocarboxylic acids: methanoic formic HCOOH ethanoic acetic CH3COOH propanoic proprionic C2H5COOH butanoic butyric C3H7COOH pentanoic valeric C4H9COOH hexanoic caproic C5H11COOH heptanoic enathic C6H13COOH octanoic caprylic C7H15COOH nonanoic pelargonic C8H17COOH decanoic capric C9H19COOH

Other simple saturated acids are found in naturally occurring glycerides. They all contain even numbers of carbon atoms: dodecanoic lauric C11H23COOH tetradecanoic myristic C13H27COOH hexadecanoic palmitic C15H31COOH octadecanoic stearic C17H35COOH eicosanoic arachidic C19H39COOH docosanoic behenic C21H43COOH tetracosanoic lignoceric C23H47COOH hexacosanoic cerotic C25H51COOH

Certain important unsaturated monocarboxylic acids occur naturally: octadec-9-enoic oleic C8H17CH=CHC7H14COOH octadeca-9,12- dienoic linoleic C5H11CH=CHCH2CH=CHC7H1 4COOH octadeca-9,12,15- trienoic linolenic C2H5CH=CHCH2CH=CHCH2CH=CH- C 7H14COOH

There are a number of common saturated dicarboxylic acids: ethanedioic oxalic HOOCCOOH propanedioic malonic HOOCCH2COOH butanedioic succinic HOOCC2H4COOH pentanedioic glutaric HOOCC3H6COOH hexanedioic adipic HOOCC4H8COOH

297 Appendix I

Examples of unsaturated dicarboxylic acids are: cis-butenedioic maleic HOOCCH=CHCOOH trans-butenedioic fumaric HOOCCH=CHCOOH

Certain hydroxy acids occur naturally: hydroxyethanoic glycolic CH2(OH)COOH 2-hydroxypropanoic lactic CH3CH(OH)COOH hydroxybutanedioic malic CH(OH)CH2(COOH)2 2-hydroxy-propane-1,2,3-tricarboxylic citric (CH2)2C(OH)(COOH)3

Naturally occurring amino carboxylic acids are shown in Appendix II.

298 Appendix II Amino Acids

NH CH 3 H COOH C 2NH H2 H N C 2 NH H C 2 C H COOH C H2 alanine arginine NH alanine arginine 2

H H2 2 O C H COOH O C H COOH C C

NH OH 2 NH2 NH2

asparagineasparagine aspartineaspartic acid

HOOC H H2 2 C C H COOH C H COOH C C SH H2

NH2 NH2 glutamic acid cysteinecysteine glutamic acid

H COOH NH 2 CH 2 C 2 C H COOH C H2 NH2 NH glutamineglutamine 2 glycineglycine

299 Appendix II Amino Acids

O CH O H2 3 C H COOH N C COOH C 3CH H C H C CH H CH NH 2 N 2 NH H 2

histidine isoleucine histidine isoleucine

H 2NH 2 H C H2 2 C CH C COOH C 3 H H H C H COOH C C 2 C H2 CH NH 3 2 NH2

leucine lysine leucine lysine

H H 2 C C S H 2 CH H COOH 3CH C C C H COOH H C 2 CH CH NH C 2 NH2 H

methionine phenylalanine methionine phenylalanine

H 2 H C H COOH 2 C C H COOH 2CH OH C NH C NH2 H2 proline serine proline serine

300 Appendix II Amino Acids

H H OH C C H2 C H COOH C CH C H H COOH 3CH C C H CH NH2 NH N 2 H threoninethreonine tryptophantryptophan

H CH H 2 3 C C CH H COOH C COOH C H H 3CH C CH NH2 OH C NH2 H

tyrosine valine tyrosine valine

301 Appendix III Sugars

Some simple monosaccharides. The β-D-form is shown in each case

H H O OH HOCH2 O OH H H OH HO HO H CH2OH OH H OH β arabinose fructose

HOCH2 HOCH2 HO O OH O OH

OH OH HO OH OH

galactose glucose

O OH HOCH2 O OH OH HO

OH OH OH

ribose xylose

302 Appendix IV

Nitrogenous Bases and Nucleosides

NH2 NH2 N 6 N N N1 7 3 9 N N N N H HOCH2 O adenine

OH OH

adenosine

O O

6 N N HN175 HN 8 2 4 9 3 N N H2N N H2N N H HOCH2 O guanine

OHOH

guanosine

O O H3C H3C NH NH N O N O HOCH O H 2

thymine

thymidine

303 Appendix IV Nitrogenous Bases and Nucleosides

NH2 NH2 N 3 N 1 N O N O H HOCH2 O cytosine

OH OH

cytidine

O O

HN HN

O N O N H HOCH O uracil 2

OH OH

uridine

304 Appendix V

The Chemical Elements (* indicates the nucleon number of the most stable isotope)

Element Symbol p.n. r.a.m Element Symbol p.n. r.a.m actinium Ac 89 227* europium Eu 63 151.965 aluminum Al 13 26.982 fermium Fm 100 257* americium Am 95 243* fluorine F 9 18.9984 antimony Sb 51 112.76 francium Fr 87 223* argon Ar 18 39.948 gadolinium Gd 64 157.25 arsenic As 33 74.92 gallium Ga 31 69.723 astatine At 85 210 germanium Ge 32 72.61 barium Ba 56 137.327 gold Au 79 196.967 berkelium Bk 97 247* hafnium Hf 72 178.49 beryllium Be 4 9.012 hassium Hs 108 265* bismuth Bi 83 208.98 helium He 2 4.0026 bohrium Bh 107 262* holmium Ho 67 164.93 boron B 5 10.811 hydrogen H 1 1.008 bromine Br 35 79.904 indium In 49 114.82 cadmium Cd 48 112.411 iodine I 53 126.904 calcium Ca 20 40.078 iridium Ir 77 192.217 californium Cf 98 251* iron Fe 26 55.845 carbon C 6 12.011 krypton Kr 36 83.80 cerium Ce 58 140.115 lanthanum La 57 138.91 cesium Cs 55 132.905 lawrencium Lr 103 262* chlorine Cl 17 35.453 lead Pb 82 207.19 chromium Cr 24 51.996 lithium Li 3 6.941 cobalt Co 27 58.933 lutetium Lu 71 174.967 copper Cu 29 63.546 magnesium Mg 12 24.305 curium Cm 96 247* manganese Mn 25 54.938 darmstadtium Ds 110 269* meitnerium Mt 109 266* dubnium Db 105 262* mendelevium Md 101 258* dysprosium Dy 66 162.50 mercury Hg 80 200.59 einsteinium Es 99 252* molybdenum Mo 42 95.94 erbium Er 68 167.26 neodymium Nd 60 144.24

305 Appendix V The Chemical Elements Element Symbol p.n. r.a.m Element Symbol p.n. r.a.m neon Ne 10 20.179 selenium Se 34 78.96 neptunium Np 93 237.048 silicon Si 14 28.086 nickel Ni 28 58.69 silver Ag 47 107.868 niobium Nb 41 92.91 sodium Na 11 22.9898 nitrogen N 7 14.0067 strontium Sr 38 87.62 nobelium No 102 259* sulfur S 16 32.066 osmium Os 76 190.23 tantalum Ta 73 180.948 oxygen O 8 15.9994 technetium Tc 43 99* palladium Pd 46 106.42 tellurium Te 52 127.60 phosphorus P 15 30.9738 terbium Tb 65 158.925 platinum Pt 78 195.08 thallium Tl 81 204.38 plutonium Pu 94 244* thorium Th 90 232.038 polonium Po 84 209* thulium Tm 69 168.934 potassium K 19 39.098 tin Sn 50 118.71 praseodymium Pr 59 140.91 titanium Ti 22 47.867 promethium Pm 61 145* tungsten W 74 183.84 protactinium Pa 91 231.036 ununbium Uub 112 285* radium Ra 88 226.025 ununtrium Uut 113 284* radon Rn 86 222* ununquadium Uuq 114 289* rhenium Re 75 186.21 ununpentium Uup 115 288* rhodium Rh 45 102.91 ununhexium Uuh 116 292* roentgenium Rg 111 272* uranium U 92 238.03 rubidium Rb 37 85.47 vanadium V 23 50.94 ruthenium Ru 44 101.07 xenon Xe 54 131.29 rutherfordium Rf 104 261* ytterbium Yb 70 173.04 samarium Sm 62 150.36 yttrium Y 39 88.906 scandium Sc 21 44.956 zinc Zn 30 65.39 seaborgium Sg 106 263* zirconium Zr 40 91.22

306 Appendix VI 18 Kr Ar Xe He Ne Rn 2 36 18 86 10 54 18 I 0 (or VIIIB) VIIIA (or 0) F Cl At Br 17 35 17 85 9 53 symbol Lr Lu 17 71 103 VIIB VIIA S O Se 16 Po Te Uuh 34 116 16 84 8 52 Yb No 16 VIB VIA 70 102 P N Bi Sb 15 As Uup 33 115 15 83 7 51 Tm Md 15 VB VA 69 101 C Si Sn 14 Pb Ge Uuq 32 114 14 82 6 50 Er Fm 14 IVB IVA 68 100 B In Al Tl 13 Ga Uut 31 113 13 81 5 49 Es Ho 13 IIIB IIIA 67 99 12 Cd Zn Hg Uub 30 112 80 48 Cf Dy 12 IIB IIB 66 98 11 Ag Cu Au Rg 29 111 79 47 Bk Tb IB IB 11 65 97 Pt 10 Ni Pd Ds 28 110 78 46 Gd Cm 10 64 96 9 Ir Rh Co Mt 27 109 77 45 Eu 9 Am 63 95 8 Fe Hs Os Ru 26 108 76 44 VIII (or VIIIB) VIII (or VIIIA) - giving group, atomic number, and chemical Pu 8 Sm 62 94 7 Tc Re Bh Mn 25 107 75 43 7 Np Pm 61 93 VIIB VIIA 6 W Sg Cr Mo 24 106 74 42 U 6 Nd VIB VIA 60 92 5 V Ta Db Nb 23 105 73 41 groups. Older group designations are shown below. Pr Pa 5 VB VA 59 91 4 Ti Rf Zr Hf 22 104 72 40 The above is the modern recommended form of table using 18 Ce Th 4 IVB IVA 58 90 - Lu 3 Y Sc 21 39 Ac - Lr 57-71 La 89-103 La Ac 3 IIIB IIIA 57 89 2 Sr Be Ba Ca Ra Mg 20 88 12 56 4 38 2 IIA IIA 1 K H Li Fr Cs Rb Na Periodic Table of the Elements Actinides 1 19 87 11 55 3 37 Lanthanides

1 IA IA 6 7 3 6 2 5 1 4 7 Period European convention Modern form N. American convention

307 Appendix VII

The Greek Alphabet

A α alpha N ν nu B β beta Ξξxi Γγgamma O ο omikron ∆δdelta Ππ pi E ε epsilon P ρ rho Z ζ zeta Σσsigma H η eta T τ tau Θθ theta Υυupsilon I ι iota Φφ phi K κ kappa X χ chi Λλlambda Ψψpsi M µ mu Ωωomega

308 Appendix VIII

Web Sites

Chemical society web sites:

American Chemical Society www.chemistry.org

Royal Society of Chemistry www.rsc.org

The International Union of Pure and www.iupac.org Applied Chemistry

Information on nomenclature:

Queen Mary College, London www.chem.qmul.ac.uk/iupac

Advanced Chemistry Development, Inc www.acdlabs.com/iupac/nomenclature

An extensive set of organic chemistry links:

WWW Virtual Library, Chemistry Section www.liv.ac.uk/Chemistry/Links

The definitive site for the chemical elements:

WebElements Periodic Table www.webelements.com

Other resources:

Chemical Education Resource Shelf, www.umsl.edu/~chemist/books Journal of Chemical Education, University of Missouri-St. Louis

Molecule of the Month www.chm.bris.ac.uk/motm/motm.htm

The Chemistry Hypermedia Project www.chem.vt.edu/chem-ed/ at Virginia Tech vt-chem-ed.html

Biographies:

Nobel Prizes http://nobelprize.org

WWW Virtual Library www.liv.ac.uk/Chemistry/Links/ refbiog.html

309 Bibliography

Comprehensive texts covering organic chemistry:

Carey, Francis and Richard J. Sundberg. Advanced Organic Chemistry: Structure and Mechanism. 4th ed. New York: Plenum, 2000.

Carey, Francis and Richard J. Sundberg. Advanced Organic Chemistry: Reactions. 4th ed. New York: Plenum, 2000.

Clayden, Jonathon; Nick Greeves; Stuart Warren; and Peter Wothers. Organic Chem- istry. Oxford, U.K.: Oxford University Press, 2000.

McMurray, John. Organic Chemistry. 6th ed. Pacific Grove, Calif.: Brooks/Cole, 2004.

March, Jerry. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. New York: Wiley, 1992.

Volhardt, Peter K. and Neil E. Schore. Organic Chemistry: Structure and Function. 4th ed. New York: W. H. Freeman, 2003.

Comprehensive texts covering inorganic chemistry:

Cotton, F. A.; C. Murillo; G. Wilkinson; M. Bochmann; and R. Grimes. Advanced Inor- ganic Chemistry. 6th ed. New York: Wiley, 1999.

Greenwood, N. N. and A. Earnshaw. Chemistry of the Elements. Oxford, U.K.: Butter- worth-Heinemann, 1997.

Shriver, D. F. and P. W. Atkins. Inorganic Chemistry. 3rd ed. Oxford, U.K.: Oxford Uni- versity Press, 1999.

Additional useful sources:

Emsley, J. Nature's Building Blocks – An A-Z Guide to the Elements. Oxford, U.K.: Oxford University Press, 2001.

King, R.B. (ed.) Encyclopedia of Inorganic Chemistry. New York: Wiley, 1994.

An advanced text on biochemistry:

Nelson, David L. and Michael M. Cox. Lehninger Principles of Biochemistry. 3rd ed. New York: Worth Publishers, 2000.

The definitive book for physical chemistry:

Atkins, Peter and Julio de Paula. Atkins’ Physical Chemistry, 7th ed. Oxford, UK: Oxford University Press, 2004.

310