DOCSLIB.ORG

Periodic Table

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Periodic Table Periodic Table - e • Columns: Similar Valence Structure - - - e e e - e inert gases inert give give up 1 accept 2 accept 1 H give up 2 He Li Be O F Ne Adapted from Na Mg give up 3 S Cl Ar Fig. 2.6, Callister & K Ca Sc Se Br Kr Rethwisch 3e. Rb Sr Y Te I Xe Cs Ba Po At Rn Fr Ra Electropositive (more metallic) elements: Electronegative elements: Readily give up valence electrons Readily acquire valence electrons to become (+)ve ions. to become (-)ve ions. 1 Electronegativity Electronegativity (EN) •Tendency of an atom to attract/acquire an electron, i.e., accept valence electrons to become (-)ve ions (ionic bonding) or sometimes they share electrons with other atoms (metallic bonding). •Thus, it’s opposite of electropositivity (metallicity) and its trends. •Atoms are more likely to accept electrons if their outer shells are almost full, and if they are less shielded from (closer to) the nucleus. •Numerous EN scales have been proposed, but the most commonly used is the one originally devised by Pauling. EN is on a 0 to 4.0 scale, with F having the highest EN of 4.0 and Cs and Fr having the lowest with 0.7. Larger electronegativity (smaller electropositivity or metallicity) Smaller electronegativity (larger electropositivity or metallicity) 2 2 Size and Mass Size and Mass •Trends are the same as in electropositivity (metallicity). •Atomic radius increases in size going down groups because new shell is added. •Atomic radius decreases from left to right because nucleus contains more protons (↑ Z)– addition of one proton to an atom gives a stronger nuclear (greater positive) charge to the nucleus and thus the electrons are attracted more tightly to the nucleus, thus atomic radii decreases. •Ionic radius: Cations (+) : smaller than atoms Anions (-) : larger than atoms •Ions always shrink with increasing positive charge and expand with increasing negative charge. •Mass increases with atomic number (increasing # of protons in the nucleus) 3 Summary of Periodic Trends A third class of elements, the metalloids, which straddle the metal–nonmetal boundary, Zintl line (e.g.: B, Si, Ge, As, Te, and Se). 4 Bonding Generalizations Based on Periodic Trends in EN •We begin by classifying all elements as either metals or nonmetals: the ‘bold’ stepped Zintl line across the right hand side of the previous slide (table). •With elements divided up in this fashion, we establish the following rules. •First, metallic elements and metal–metal combinations form metal bonded solids. •Second, nonmetallic elements (e.g. Cl-Cl), and nonmetal–nonmetal (e.g., O-N) combinations are generally covalently bonded. •Third, bonds between metals and nonmetals are either ionic or covalent, depending on the electronegativity difference which requires calculation: •This EN difference from Pauling’s expression for the ionicity fraction of a bond (f ) is 2 -1/4(xnm-xm) f=1-e exs.: binary ZnO & BaF2… where xnm is the EN of the nonmetallic element and xm is the EN of the metallic element. •We will assume that when f > 0.5, the bonds are ionic and that when f ≤ 0.5, the bonds are covalent. In generic terms, the greater the difference between two atoms, the more ionic the bond, while the smaller the difference the more covalent the bond. •In ternary or more complex compounds, the fractional ionicity can be determined by using stoichiometrically weighted averages for the values of xm and/or xnm, ex.: In4Sn3O12… •It must be emphasized that the change from metallic to nonmetallic character is continuous and complex, so much that many authors would refute the apparently arbitrary binary categorization defined above…. 5 Bonding – Property Interrelationships •However, with such criticism noted, a binary classification is nevertheless implemented because it has the practical advantage of leading to a simple set of rules to determine bond types. •Once the bond type is defined, the type of atomic structure and properties that the solid might have can also be inferred. This relationship is illustrated schematically: •When crossing metal-nonmetal boundary, properties change dramatically with variation in bonding: 6 Origin of Bonding in Solids (Bonding Forces and Energies) •Many physical properties can be predicted based on interatomic forces that bind the atoms together. •Net force FN between atoms = FA + FR which is also function of interatomic separation. •Equilibrium exists when FA + FR become equal, there is no net force (=0), or else the atom moves. •The center of atoms will remain separated by equilibrium spacing (ro) or bond length. ~0.3 nm •Potential energies between atoms E=-∫Fdr or EN EA ER Adapted from Fig. 2.8(b), •The net E curve has a potential energy trough or Callister & Rethwisch 3e. well around its minimum. Here ro corresponds to separation distance at minimum of E curve. •The bonding energy (E0) for two atoms corresponds to energy at this minimum point. •E0 represents the energy required to separate these two atoms to an infinite separationbond strength •The magnitude of E0 and shape of the curve vary 7 from material to material & depend on type of 7 atomic bonding. ….. Review: Covalent Bonding Model •Covalent - there is valence electron sharing between two adjacent atoms such that each atom assumes a stable electron configuration. Example is methane: C: has 4 valence e-, needs 4 more •Each atom contributes at least one electron to the bond and the H: has 1 valence e-, needs 1 more shared electrons may be considered to belong to both atoms. •For methane each H atom can acquire a He electron configuration, when one of four carbon sp3 valence electrons is shared for total of 8 valence electrons (Ne electron configuration), octet rule. •The number of covalent bonds possible for a particular atom is determined by the number of valence electrons. For N' valence Adapted electrons, an atom can covalently bond with at most 8-N' other atoms. from Fig. •Examples: Cl atom has valence electron structure of 3s23p5 2.10, Callister & Rethwisch •C and Si have 2s22p2 and 3s23p2 structures, respectively. 3e. •f ≤ 0.5 (small DEN) metallic-nonmetallic elements and in crystals with nonmetallic elements. •Bonds are directional in nature: they exist only in the direction between one atom and another that participate in electron sharing. •Thus covalently bonded materials are generally less dense than ionically or metallically bonded ones (non-directional); when bonds are directional, the atoms cannot pack together in as dense a manner, thus yielding a lower mass density. 8 Examples of Covalent Bonding H2O H 2 F2 C(diamond) H He - 2.1 SiC column IVA Cl2 Li Be C O F Ne 1.0 1.5 2.5 2.0 4.0 - Na Mg Si Cl Ar 0.9 1.2 1.8 3.0 - K Ca Ti Cr Fe Ni Zn Ga Ge As Br Kr 0.8 1.0 1.5 1.6 1.8 1.8 1.8 1.6 1.8 2.0 2.8 - Rb Sr Sn I Xe 0.8 1.0 1.8 2.5 - Cs Ba Pb At Rn 0.7 0.9 1.8 2.2 - Fr Ra Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is 0.7 0.9 GaAs adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. • Molecules with nonmetals, e.g. Cl2, F2, O2 • Elemental solids (RHS of Periodic Table), e.g. C, P, S, I • Compound solids with metals and nonmetals, e.g. ZnO, GaAs,GaP • Compound solids (about column IVA), e.g. SiC 9 Simple Bonding Models – Covalent (continued) The molecular solid has covalent bonds (dark lines) only within individual There is a covalently bonded molecules. Thus, there is no path between any two atoms, covalently bonded path e.g. 1 and 2. between the atom labeled 1 and the atom labeled 2; the molecules are bonded to one another only by weak Covalently bonded 3-D network such as Si, secondary forces. SiC, BN, etc. Molecular solids or polymeric solids such as •All atoms are linked by covalent bonds, i.e., crystalline materials C60, H2O, and there is a covalently bonded path between any macromolecular solids polyethylene. 2 atoms in the solid. •Atoms within each molecule are linked by covalent bonds, but the molecules that make up the crystal are held together only by the weak interactions known collectively as intermolecular forces or secondary bonds (including van der Waals, dipolar, and hydrogen bond). •In such solids, not all atoms are connected by a path of strong covalent bonds. •“Rule of Thumb”: if more than two thirds of the components in a covalently bonded compound are H, C, O, N, or a halogen, then it is likely to be a molecular solid. •However, diamond is a noteworthy example illustrating that this guideline should be applied 10 with caution. Covalent Bonding Model (continued) •Simple model assumes that electrons are shared between atoms and that electron charge density accumulates between the relatively positive atomic cores. •Defining characteristic of a covalent bond is the existence of a local maximum in the valence electron density in the regions between the atomic cores. For example, experimentally measured charged density in Si is shown: •The peak in electron density (.69) at the midpoint connecting the two Si nuclei is signature of the covalent bond. Fig. Valence electron density map in the •Concentrating the valence electrons in the spaces between {110} plane of Si. Contours are at 0.1 e/Å3. The shape of the peaks are the atomic cores is clearly distinct from the ionic bonding theoretically predicted and also found in model, where the valence electrons are centered on the anion many III-V semiconductors, e.g.
Load more

Recommended publications
  • The Dependence of the Sio Bond Length on Structural Parameters in Coesite, the Silica Polymorphs, and the Clathrasils
    American Mineralogist, Volume 75, pages 748-754, 1990 The dependence of the SiO bond length on structural parameters in coesite, the silica polymorphs, and the clathrasils M. B. BOISEN, JR. Department of Mathematics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, U.S.A. G. V. GIBBS, R. T. DOWNS Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, U.S.A. PHILIPPE D' ARCO Laboratoire de Geologie, Ecole Normale Superieure, 75230 Paris Cedex OS, France ABSTRACT Stepwise multiple regression analyses of the apparent R(SiO) bond lengths were com- pleted for coesite and for the silica polymorphs together with the clathrasils as a function of the variables};(O), P (pressure), f,(Si), B(O), and B(Si). The analysis of 94 bond-length data recorded for coesite at a variety of pressures and temperatures indicates that all five of these variables make a significant contribution to the regression sum of squares with an R2 value of 0.84. A similar analysis of 245 R(SiO) data recorded for silica polymorphs and clathrasils indicate that only three of the variables (B(O), };(O), and P) make a signif- icant contribution to the regression with an R2 value of 0.90. The distribution of B(O) shows a wide range of values from 0.25 to 10.0 A2 with nearly 80% of the observations clustered between 0.25 and 3.0 A2 and the remaining values spread uniformly between 4.5 and 10.0 A2. A regression analysis carried out for these two populations separately indicates, for the data set with B(O) values less than three, that };(O) B(O), P, and };(Si) are all significant with an R2 value of 0.62.
    [Show full text]
  • The Periodic Electronegativity Table
    The Periodic Electronegativity Table Jan C. A. Boeyens Unit for Advanced Study, University of Pretoria, South Africa Reprint requests to J. C. A. Boeyens. E-mail: [email protected] Z. Naturforsch. 2008, 63b, 199 – 209; received October 16, 2007 The origins and development of the electronegativity concept as an empirical construct are briefly examined, emphasizing the confusion that exists over the appropriate units in which to express this quantity. It is shown how to relate the most reliable of the empirical scales to the theoretical definition of electronegativity in terms of the quantum potential and ionization radius of the atomic valence state. The theory reflects not only the periodicity of the empirical scales, but also accounts for the related thermochemical data and serves as a basis for the calculation of interatomic interaction within molecules. The intuitive theory that relates electronegativity to the average of ionization energy and electron affinity is elucidated for the first time and used to estimate the electron affinities of those elements for which no experimental measurement is possible. Key words: Valence State, Quantum Potential, Ionization Radius Introduction electronegative elements used to be distinguished tra- ditionally [1]. Electronegativity, apart from being the most useful This theoretical notion, in one form or the other, has theoretical concept that guides the practising chemist, survived into the present, where, as will be shown, it is also the most bothersome to quantify from first prin- provides a precise definition of electronegativity. Elec- ciples. In historical context the concept developed in a tronegativity scales that fail to reflect the periodicity of natural way from the early distinction between antag- the L-M curve will be considered inappropriate.
    [Show full text]
  • An Alternate Graphical Representation of Periodic Table of Chemical Elements Mohd Abubakr1, Microsoft India (R&D) Pvt
    An Alternate Graphical Representation of Periodic table of Chemical Elements Mohd Abubakr1, Microsoft India (R&D) Pvt. Ltd, Hyderabad, India. [email protected] Abstract Periodic table of chemical elements symbolizes an elegant graphical representation of symmetry at atomic level and provides an overview on arrangement of electrons. It started merely as tabular representation of chemical elements, later got strengthened with quantum mechanical description of atomic structure and recent studies have revealed that periodic table can be formulated using SO(4,2) SU(2) group. IUPAC, the governing body in Chemistry, doesn‟t approve any periodic table as a standard periodic table. The only specific recommendation provided by IUPAC is that the periodic table should follow the 1 to 18 group numbering. In this technical paper, we describe a new graphical representation of periodic table, referred as „Circular form of Periodic table‟. The advantages of circular form of periodic table over other representations are discussed along with a brief discussion on history of periodic tables. 1. Introduction The profoundness of inherent symmetry in nature can be seen at different depths of atomic scales. Periodic table symbolizes one such elegant symmetry existing within the atomic structure of chemical elements. This so called „symmetry‟ within the atomic structures has been widely studied from different prospects and over the last hundreds years more than 700 different graphical representations of Periodic tables have emerged [1]. Each graphical representation of chemical elements attempted to portray certain symmetries in form of columns, rows, spirals, dimensions etc. Out of all the graphical representations, the rectangular form of periodic table (also referred as Long form of periodic table or Modern periodic table) has gained wide acceptance.
    [Show full text]
  • Unit 3 Notes: Periodic Table Notes  John Newlands Proposed an Organization System Based on Increasing Atomic Mass in 1864
    Unit 3 Notes: Periodic Table Notes John Newlands proposed an organization system based on increasing atomic mass in 1864. He noticed that both the chemical and physical properties repeated every 8 elements and called this the ____Law of Octaves ___________. In 1869 both Lothar Meyer and Dmitri Mendeleev showed a connection between atomic mass and an element’s properties. Mendeleev published first, and is given credit for this. He also noticed a periodic pattern when elements were ordered by increasing ___Atomic Mass _______________________________. By arranging elements in order of increasing atomic mass into columns, Mendeleev created the first Periodic Table. This table also predicted the existence and properties of undiscovered elements. After many new elements were discovered, it appeared that a number of elements were out of order based on their _____Properties_________. In 1913 Henry Mosley discovered that each element contains a unique number of ___Protons________________. By rearranging the elements based on _________Atomic Number___, the problems with the Periodic Table were corrected. This new arrangement creates a periodic repetition of both physical and chemical properties known as the ____Periodic Law___. Periods are the ____Rows_____ Groups/Families are the Columns Valence electrons across a period are There are equal numbers of valence in the same energy level electrons in a group. 1 When elements are arranged in order of increasing _Atomic Number_, there is a periodic repetition of their physical and chemical
    [Show full text]
  • The Periodic Table
    THE PERIODIC TABLE Dr Marius K Mutorwa [email protected] COURSE CONTENT 1. History of the atom 2. Sub-atomic Particles protons, electrons and neutrons 3. Atomic number and Mass number 4. Isotopes and Ions 5. Periodic Table Groups and Periods 6. Properties of metals and non-metals 7. Metalloids and Alloys OBJECTIVES • Describe an atom in terms of the sub-atomic particles • Identify the location of the sub-atomic particles in an atom • Identify and write symbols of elements (atomic and mass number) • Explain ions and isotopes • Describe the periodic table – Major groups and regions – Identify elements and describe their properties • Distinguish between metals, non-metals, metalloids and alloys Atom Overview • The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) – He believed that atoms were indivisible and indestructible – His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy John Dalton(1766-1844) In 1803, he proposed : 1. All matter is composed of atoms. 2. Atoms cannot be created or destroyed. 3. All the atoms of an element are identical. 4. The atoms of different elements are different. 5. When chemical reactions take place, atoms of different elements join together to form compounds. J.J.Thomson (1856-1940) 1. Proposed the first model of the atom. 2. 1897- Thomson discovered the electron (negatively- charged) – cathode rays 3. Thomson suggested that an atom is a positively- charged sphere with electrons embedded in it.
    [Show full text]
  • The Development of the Periodic Table and Its Consequences Citation: J
    Firenze University Press www.fupress.com/substantia The Development of the Periodic Table and its Consequences Citation: J. Emsley (2019) The Devel- opment of the Periodic Table and its Consequences. Substantia 3(2) Suppl. 5: 15-27. doi: 10.13128/Substantia-297 John Emsley Copyright: © 2019 J. Emsley. This is Alameda Lodge, 23a Alameda Road, Ampthill, MK45 2LA, UK an open access, peer-reviewed article E-mail: [email protected] published by Firenze University Press (http://www.fupress.com/substantia) and distributed under the terms of the Abstract. Chemistry is fortunate among the sciences in having an icon that is instant- Creative Commons Attribution License, ly recognisable around the world: the periodic table. The United Nations has deemed which permits unrestricted use, distri- 2019 to be the International Year of the Periodic Table, in commemoration of the 150th bution, and reproduction in any medi- anniversary of the first paper in which it appeared. That had been written by a Russian um, provided the original author and chemist, Dmitri Mendeleev, and was published in May 1869. Since then, there have source are credited. been many versions of the table, but one format has come to be the most widely used Data Availability Statement: All rel- and is to be seen everywhere. The route to this preferred form of the table makes an evant data are within the paper and its interesting story. Supporting Information files. Keywords. Periodic table, Mendeleev, Newlands, Deming, Seaborg. Competing Interests: The Author(s) declare(s) no conflict of interest. INTRODUCTION There are hundreds of periodic tables but the one that is widely repro- duced has the approval of the International Union of Pure and Applied Chemistry (IUPAC) and is shown in Fig.1.
    [Show full text]
  • Removal of Heavy Metals from Aqueous Solution by Zeolite in Competitive Sorption System
    International Journal of Environmental Science and Development, Vol. 3, No. 4, August 2012 Removal of Heavy Metals from Aqueous Solution by Zeolite in Competitive Sorption System Sabry M. Shaheen, Aly S. Derbalah, and Farahat S. Moghanm rich volcanic rocks (tuff) with fresh water in playa lakes or Abstract—In this study, the sorption behaviour of natural by seawater [5]. (clinoptilolite) zeolites with respect to cadmium (Cd), copper The structures of zeolites consist of three-dimensional (Cu), nickel (Ni), lead (Pb) and zinc (Zn) has been studied in frameworks of SiO and AlO tetrahedra. The aluminum ion order to consider its application to purity metal finishing 4 4 wastewaters. The batch method has been employed, using is small enough to occupy the position in the center of the competitive sorption system with metal concentrations in tetrahedron of four oxygen atoms, and the isomorphous 4+ 3+ solution ranging from 50 to 300 mg/l. The percentage sorption replacement of Si by Al produces a negative charge in and distribution coefficients (Kd) were determined for the the lattice. The net negative charge is balanced by the sorption system as a function of metal concentration. In exchangeable cation (sodium, potassium, or calcium). These addition lability of the sorbed metals was estimated by DTPA cations are exchangeable with certain cations in solutions extraction following their sorption. The results showed that Freundlich model described satisfactorily sorption of all such as lead, cadmium, zinc, and manganese [6]. The fact metals. Zeolite sorbed around 32, 75, 28, 99, and 59 % of the that zeolite exchangeable ions are relatively innocuous added Cd, Cu, Ni, Pb and Zn metal concentrations (sodium, calcium, and potassium ions) makes them respectively.
    [Show full text]
  • The Nafure of Silicon-Oxygen Bonds
    AmericanMineralogist, Volume 65, pages 321-323, 1980 The nafure of silicon-oxygenbonds LtNus PeurrNc Linus Pauling Institute of Scienceand Medicine 2700 Sand Hill Road, Menlo Park, California 94025 Abstract Donnay and Donnay (1978)have statedthat an electron-densitydetermination carried out on low-quartz by R. F. Stewart(personal communication), which assignscharges -0.5 to the oxygen atoms and +1.0 to the silicon atoms, showsthe silicon-oxygenbond to be only 25 percentionic, and hencethat "the 50/50 descriptionofthe past fifty years,which was based on the electronegativity difference between Si and O, is incorrect." This conclusion, however, ignoresthe evidencethat each silicon-oxygenbond has about 55 percentdouble-bond char- acter,the covalenceof silicon being 6.2,with transferof 2.2 valenc,eelectrons from oxygen to silicon. Stewart'svalue of charge*1.0 on silicon then leads to 52 percentionic characterof the bonds, in excellentagreement with the value 5l percent given by the electronegativity scale. Donnay and Donnay (1978)have recently referred each of the four surrounding oxygen atoms,this ob- to an "absolute" electron-densitydetermination car- servationleads to the conclusionthat the amount of ried out on low-quartz by R. F. Stewart, and have ionic character in the silicon-oxygsa 5ingle bond is statedthat "[t showsthe Si-O bond to be 75 percent 25 percent. It is, however,not justified to make this covalent and only 25 percent ionic; the 50/50 de- assumption. scription of the past fifty years,which was basedon In the first edition of my book (1939)I pointed out the electronegativitydifference between Si and O, is that the observedSi-O bond length in silicates,given incorrect." as 1.604, is about 0.20A less than the sum of the I formulated the electronegativityscale in 1932, single-bond radii of the two atoms (p.
    [Show full text]
  • Chapter 7 Electron Configuration and the Periodic Table
    Chapter 7 Electron Configuration and the Periodic Table Copyright McGraw-Hill 2009 1 7.1 Development of the Periodic Table • 1864 - John Newlands - Law of Octaves- every 8th element had similar properties when arranged by atomic masses (not true past Ca) • 1869 - Dmitri Mendeleev & Lothar Meyer - independently proposed idea of periodicity (recurrence of properties) Copyright McGraw-Hill 2009 2 • Mendeleev – Grouped elements (66) according to properties – Predicted properties for elements not yet discovered – Though a good model, Mendeleev could not explain inconsistencies, for instance, all elements were not in order according to atomic mass Copyright McGraw-Hill 2009 3 • 1913 - Henry Moseley explained the discrepancy – Discovered correlation between number of protons (atomic number) and frequency of X rays generated – Today, elements are arranged in order of increasing atomic number Copyright McGraw-Hill 2009 4 Periodic Table by Dates of Discovery Copyright McGraw-Hill 2009 5 Essential Elements in the Human Body Copyright McGraw-Hill 2009 6 The Modern Periodic Table Copyright McGraw-Hill 2009 7 7.2 The Modern Periodic Table • Classification of Elements – Main group elements - “representative elements” Group 1A- 7A – Noble gases - Group 8A all have ns2np6 configuration(exception-He) – Transition elements - 1B, 3B - 8B “d- block” – Lanthanides/actinides - “f-block” Copyright McGraw-Hill 2009 8 Periodic Table Colored Coded By Main Classifications Copyright McGraw-Hill 2009 9 Copyright McGraw-Hill 2009 10 • Predicting properties – Valence
    [Show full text]
  • Constraint Closure Drove Major Transitions in the Origins of Life
    entropy Article Constraint Closure Drove Major Transitions in the Origins of Life Niles E. Lehman 1 and Stuart. A. Kauffman 2,* 1 Edac Research, 1879 Camino Cruz Blanca, Santa Fe, NM 87505, USA; [email protected] 2 Institute for Systems Biology, Seattle, WA 98109, USA * Correspondence: [email protected] Abstract: Life is an epiphenomenon for which origins are of tremendous interest to explain. We provide a framework for doing so based on the thermodynamic concept of work cycles. These cycles can create their own closure events, and thereby provide a mechanism for engendering novelty. We note that three significant such events led to life as we know it on Earth: (1) the advent of collective autocatalytic sets (CASs) of small molecules; (2) the advent of CASs of reproducing informational polymers; and (3) the advent of CASs of polymerase replicases. Each step could occur only when the boundary conditions of the system fostered constraints that fundamentally changed the phase space. With the realization that these successive events are required for innovative forms of life, we may now be able to focus more clearly on the question of life’s abundance in the universe. Keywords: origins of life; constraint closure; RNA world; novelty; autocatalytic sets 1. Introduction The plausibility of life in the universe is a hotly debated topic. As of today, life is only known to exist on Earth. Thus, it may have been a singular event, an infrequent event, or a common event, albeit one that has thus far evaded our detection outside our own planet. Herein, we will not attempt to argue for any particular frequency of life.
    [Show full text]
  • Basic Concepts of Chemical Bonding
    Basic Concepts of Chemical Bonding Cover 8.1 to 8.7 EXCEPT 1. Omit Energetics of Ionic Bond Formation Omit Born-Haber Cycle 2. Omit Dipole Moments ELEMENTS & COMPOUNDS • Why do elements react to form compounds ? • What are the forces that hold atoms together in molecules ? and ions in ionic compounds ? Electron configuration predict reactivity Element Electron configurations Mg (12e) 1S 2 2S 2 2P 6 3S 2 Reactive Mg 2+ (10e) [Ne] Stable Cl(17e) 1S 2 2S 2 2P 6 3S 2 3P 5 Reactive Cl - (18e) [Ar] Stable CHEMICAL BONDSBONDS attractive force holding atoms together Single Bond : involves an electron pair e.g. H 2 Double Bond : involves two electron pairs e.g. O 2 Triple Bond : involves three electron pairs e.g. N 2 TYPES OF CHEMICAL BONDSBONDS Ionic Polar Covalent Two Extremes Covalent The Two Extremes IONIC BOND results from the transfer of electrons from a metal to a nonmetal. COVALENT BOND results from the sharing of electrons between the atoms. Usually found between nonmetals. The POLAR COVALENT bond is In-between • the IONIC BOND [ transfer of electrons ] and • the COVALENT BOND [ shared electrons] The pair of electrons in a polar covalent bond are not shared equally . DISCRIPTION OF ELECTRONS 1. How Many Electrons ? 2. Electron Configuration 3. Orbital Diagram 4. Quantum Numbers 5. LEWISLEWIS SYMBOLSSYMBOLS LEWISLEWIS SYMBOLSSYMBOLS 1. Electrons are represented as DOTS 2. Only VALENCE electrons are used Atomic Hydrogen is H • Atomic Lithium is Li • Atomic Sodium is Na • All of Group 1 has only one dot The Octet Rule Atoms gain, lose, or share electrons until they are surrounded by 8 valence electrons (s2 p6 ) All noble gases [EXCEPT HE] have s2 p6 configuration.
    [Show full text]
  • Atomic Structures of the M Olecular Components in DNA and RNA Based on Bond Lengths As Sums of Atomic Radii
    1 Atomic St ructures of the M olecular Components in DNA and RNA based on Bond L engths as Sums of Atomic Radii Raji Heyrovská (Institute of Biophysics, Academy of Sciences of the Czech Republic) E-mail: [email protected] Abstract The author’s interpretation in recent years of bond lengths as sums of the relevant atomic/ionic radii has been extended here to the bonds in the skeletal structures of adenine, guanine, thymine, cytosine, uracil, ribose, deoxyribose and phosphoric acid. On examining the bond length data in the literature, it has been found that the averages of the bond lengths are close to the sums of the corresponding atomic covalent radii of carbon (tetravalent), nitrogen (trivalent), oxygen (divalent), hydrogen (monovalent) and phosphorus (pentavalent). Thus, the conventional molecular structures have been resolved here (for the first time) into probable atomic structures. 1. Introduction The interpretation of the bond lengths in the molecules constituting DNA and RNA have been of interest ever since the discovery [1] of the molecular structure of nucleic acids. This work was motivated by the earlier findings [2a,b] that the inter-atomic distance between any two atoms or ions is, in general, the sum of the radii of the atoms (and or ions) constituting the chemical bond, whether the bond is partially or fully ionic or covalent. It 2 was shown in [3] that the lengths of the hydrogen bonds in the Watson- Crick [1] base pairs (A, T and C, G) of nucleic acids as well as in many other inorganic and biochemical compounds are sums of the ionic or covalent radii of the hydrogen donor and acceptor atoms or ions and of the transient proton involved in the hydrogen bonding.
    [Show full text]