Brief History Leading to Atomic View of Matter

AT Chemistry 2013Chapter 2 Notes Atoms, Molecules and IonsBrief History Leading to Atomic View of Matter: Aristotle:Democritus:Alchemy:Robert Boyle: quantitative physical experiments ("The Skeptical Chemist")Joseph Priestly: HgO(s)  Hg(l) + O2(g) (discovered oxygen – air cannot be an “element”.Henry Cavendish: Zn + HCl(aq)  ZnCl2(aq) + H2(g) (discovered hydrogen)FUNDAMENTAL CHEMICAL LAWS* Law of Conservation of Mass (Laviosier)MASS reactants = MASS productsIn a combustion reaction, 46.0 g of ethanol reacts with 96.0 g of oxygen to produce water and carbon dioxide. If 54.0 g of water is produced, how much carbon dioxide is produced? * Law of Definite Proportions (Proust)A given compound always contains exactly the same proportion of elements by weight. e.g. water = 11% H and 89% O by mass. Another way of saying this is that the ratios of the masses of the elements in a compound are constant.A sample of choloroform is found to contain 12.0 g of carbon, 106.4 g of chlorine, and 1.01 g of hydrogen. If a second sample of chloroform is found to contain 30.0 g of carbon, how many grams of chlorine and grams of hydrogen does it contain?* Law of Multiple proportions (Dalton)When two elements form a series of compounds, the ratio of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.Mass of oxygen that combines with 1 gram of tin compound I 0.13 g SnO compound II 0.26 g SnO2Water, H2O, contains 2.02 g of hydrogen and 16.0 g of oxygen. Hydrogen peroxide, H2O2, contains 2.02 g of hydrogen and 32.0 g oxygen. Show how these data illustrate the law of multiple proportions.Text problem 352 Dalton's Atomic Theory (1808)1. Each element is made up of tiny indivisible particles called atoms.2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.3. Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms. 4. Chemical reactions involve reorganization of atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.Law of Combining Volumes (Guy-Lusaac):Under the same conditions of temperature and pressure, gases are found to react in simple proportions by volume, and the volume of any gaseous products bears a whole- number ratio to that of any gaseous reactant. Thus,2 volumes hydrogen + 1 volume oxygen  2 volumes water (at constant temperature and pressure)Avogadro's Hypothesis:3 At the same temperature and pressure, equal volumes of different gases contain the same number of particles.2 volumes hydrogen + 1 volume oxygen  2 volumes water2 molecules hydrogen + 1 molecule oxygen  2 molecules waterSome Observations Experiments That Led to the Nuclear Model of the AtomDuring the century that Dalton’s atomic model, evidence accumulated which indicated that atoms had structure (i.e. an atom consisted of subatomic particles). What was this evidence?J.J. Thompson - classic experiment in which he subjected a cathode ray (a beam of electrons exhibiting both wave and particle properties) to perpendicular electric and magnetic fields inside an (almost) evacuated vessel.Thompson realized that the amount of deflection is directly proportional to charge and inversely proportional to mass; by adjusting the direction and strength of the magnetic field, he caused the deflected beam to return to its original position. When this occurred the force of electric field = force of magnetic field. He set the variables describing both forces into an equation which had two unknowns: the charge and mass of the electron. He solved for the charge to mass ratio:8 Felectric = Fmagnetic from this, e/m = 1.759 X 10 C/g e = charge of electron m = mass of electron Robert Millikan - famous "oil-drop" experiment in determining the charge on the electron. Millikan obtained a mist of very fine oil drops by spraying oil from an atomizer4 in a chamber containing two electrically charged plates. Those oil drops that fell through the hole of the positive plate were zapped with high energy waves (X-rays) which carry enough energy to knock off the outermost electrons from the oil drops (i.e. to ionize them). This leaves positively charged oil drops (which immediately descend to the negative plate) and free electrons flying around. Now some of these electrons are absorbed by other oil drops (in whole numbers of electrons) and these oil drops become negatively charged. The negatively charged oil drops have two opposing forces acting on them: the force of gravity pulling them down and the electric force on the negative plate repelling them back up. If the electric charge on the plate is adjusted just so that the charge remains suspended between the plates (as viewed through the eyepiece) then we can say the two forces equal each other. Now using the variables representing these forces and setting them equal to each other in an equation, Millikan was able to determine the charge on the oil drops. He found this number to be 1.60 X 10-19 C (or some multiple of 1.60 - representing two or more electrons on an oil drop).Fweight = Felectric m = mass of oil drop M x g = E x e g = gravitational constant m g e = g E E = charge on plates e = 1.60 X 10-19C e = charge on oil dropThen from Thompson’s e/m ratio we can calculate the mass of an electron: m = 1.60 X 10-19C/1.759 X 108C/g = 9.11 X 10-28 g5 Thomson recognized that if atoms contained negatively charged electrons then they must contain an equal amount of positive charge. Since the electrons made such a small mass contribution, he speculated that the positive portion contributed not only most of the mass, but also most of the volume of an atom. His model of the atom was a sphere of positively charged matter in which tiny electrons were embedded (the “plum-pudding” model). At the time, this was consistent with experimental evidence.Ernst Rutherford – conducted an experiment that was expected to support Thomson’s model. Alpha particles (or helium nuclei) are emitted by some radioactive substances. When these alpha particles were allowed to strike a thin gold foil (only a few atoms thick), most of the alpha particles passed through and a small percentage was deflected. The degree of deflections was measured. The Thomson model, with its diffuse distribution of positive charge, predicted that only small deflections of the positive, but quite massive, alpha particle would occur. This is what was mostly observed, but once in a while an alpha particle was deflected by a large angle (even 180o!). THIS was incredible! Rutherford likened this behavior to a “15 inch shell fired at a piece of tissue paper and bouncing back”. He concluded that something incredibly dense and positively charged was present in the atom. Rutherford proposed that all of the positive charge and most of the mass of an atom is concentrated within an extremely small central region which he called the nucleus. This experiment became known as the classic "Gold-Foil" experiment in which Rutherford proposed a nuclear model of the atom. (See schematic next page). A valid size analogy would be comparing the size of a baseball (the nucleus) ion the middle of Yankee stadium (the atom). Rutherford was able to discover that the positive charge in a nucleus was due to a particle that we call a proton. The proton has a charge equal in magnitude, but opposite in sign, to the charge of an electron. The proton is approximately 2000 times more massive than the electron, as one would expect from the properties of hydrogen. However, the helium atom was known to possess only two electrons and two protons and the ratio of the nuclear mass to electron mass (about 4000:1) was too high! This ratio was observed to also be too high in atoms of other elements. The resolution of this difficulty was to propose that there must be another massive, but uncharged, particle in the nucleus. This particle, called the neutron, was not experimentally verified until the 1930’s due to the difficulty of detecting an uncharged particle.6 Conclusions:1. atoms are mostly empty space - most alpha particles were not deflected 2. alpha particles deflected came close to a concentration of positive charge - the nucleus7 note: 1 atomic mass unit (amu) = 1.66 X 10-24 gModern Atomic StructureAX Z X = the element symbol Z = atomic number = number of protons A = mass number = number of protons plus neutronsFill in the following table:Symbol Protons Neutrons Electrons Charge MassS2- ______32.0______56 81 54 ______Cl- ______20 ______Text problems 53, 55, 59NAMING COMPOUNDS 8 YOU MUST MEMORIZE the names and charges of the following ions:1 + 2 + 3 + + 2+ 3+ ammonium NH4 barium Ba aluminum Al cesium Cs+ beryllium Be2+ chromium(III) Cr3+ copper(I) Cu+ cadmium Cd2+ cobalt(III) Co3+ potassium K+ calcium Ca2+ iron(III) Fe3+ silver Ag+ cobalt(II) Co2+ nickel(III) Ni3+ sodium Na+ copper(II) Cu2+ iron(II) Fe2+ lead(II) Pb2+ magnesium Mg2+ 2+ mercury(I) Hg2 mercury(II) Hg2+ nickel Ni2+ strontium Sr2+ zinc Zn2+1 - 2 - 3 - - 2- 3- acetate C2H3O2 carbonate CO3 phosphate PO4 - 2- 3- bromate BrO3 chromate CrO4 nitride N - 2- bromide Br dichromate Cr2O7 - 2- chlorate ClO3 oxalate C2O4 - 2- chlorite ClO2 oxide O - 2- chloride Cl peroxide O2 - 2- cyanide CN sulfate SO4 fluoride F- sulfide S2- - 2- hydrogen carbonate HCO3 sulfite SO3 2- (bicarbonate) tartrate C4H4O6 - 2- hydrogen sulfate HSO4 thiosulfate S2O3 hydroxide OH- iodide I- - iodate IO3 - nitrate NO3 - nitrite NO2 - permanganate MnO4 hydride H-Symbol Name Symbol Traditional Stock9 Co cobalt Co2+ cobaltous cobalt(II) Co3+ cobaltic cobalt(III)Cu copper Cu+ cuprous copper(I) Cu2+ cupric copper(II)Fe iron Fe2+ ferrous iron(II) Fe3+ ferric iron(III)2+ Hg mercury Hg2 mercurous mercury(I) Hg2+ mercuric mercury(II)Pb lead Pb2+ plumbous lead(II) Pb4+ plumbic lead(IV)Sn tin Sn2+ stannous tin(II) Sn4+ stannic tin(IV) ------1. Binary SaltsA binary salt contains only one kind of cation (positive ion) and one kind of anion (negative ion).Cations fall into two general classes: elements that ionize to only one oxidation state and those that can ionize to form several oxidation states (designated with roman numerals in parentheses). The cation name is the name of the element plus the word "ion". In the case of cations with multiple oxidation states the number of the oxidation state is included.The oxidation numbers for elements within the following groups is summarized:Group 1 = +1 2 = +2 13 = +3 15 = -3 for N and -3 for P 16 = -2 17 = -1Anions that are made up of a single element are named by replacing the suffix with "ide."The process of naming binary salts involves combining names which you separately assign to the cation and anion halves. The only complication can be with determining whether the cation requires a roman numeral. For those catoions that can have more than10 one oxidation number we need to use Roman numerals top designate the charge on the cation. Keep in mind: a) The cation always comes first in a name b) the total charge on a compound must equal zero. example: calcium fluoride: ______PbS2: ____________ iron (III) chloride: ______Hg2I2: ____________Text problems 63, 652. Ternary Salts (salts with polyatomic ions)The same rules are followed when naming compounds involving polyatomic ions as when naming binary salts. The only thing to keep in mind is that you don't change the name of the polyatomic ion. In writing formulas, if you need to take the polyatomic ions more than once to balance charge, you then write it in parentheses with the subscript outside the parentheses.Certain polyatomic anions contain different numbers of oxygen atoms combined with an atom of a different element. These are called oxyanions. An oxyanion series normally contains either 2 or 4 members. In a two member series, the anion with more oxygens gets the suffix "ate," and the one with fewer oxygens gets the suffix "ite." When there are 4 atoms in the series, the sequence is:IO- = hypoiodite - IO2 = iodite - IO3 = iodate - IO4 = periodateExamples: NaBrO4 = ______KIO3= ______KMnO4 = ______3. Binary Covalent CompoundsSuch compounds are formed between two nonmetals. These compounds can be named using prefixes. Remember not to put mono in front of a single cation. The binary11 covalent compound IF5, for example, could be named iodine pentafluoride. Using the stock system we name it iodine(V) fluoride. Recall. 1 = mono, 2 = di, 3 = tri, 4 = tetra, 5 = penta, 6 = hexa, 7 = hepta, 8 = octa, 9 = nona, 10 = deca traditional stockSO3CON2O5PCl3Text problems 67, 71, 73, 75, 764. AcidsFor now, we can define an acid as any substance containing hydrogen as the only cation. To name an acid, determine if the anion contains oxygen (in which case it is called an oxyanion). If the anion does not contain oxygen, a. change the "ide" suffix to "ic acid," b. add the prefix "hydro" to the beginning of the name- For example, H2S is named hydrosulfuric acid. The one exception to the rule is CN (HCN is named hydrocyanic acid).If the anion contain oxygen, a. If the anion suffix is "ite," change it to "ous acid." b. If the anion suffic is "ate,", change it to "ic acid." Examples: a) HF ______b) HC2H3O2 ______c) HBrO3 ______d) HBrO ______e) HI ______12 f) HNO2 ______Additional Problems:1. AlI3 ______2. Cd(HCO3)2 ______3. NaH ______4. V2O5 ______5. P4O6 ______6. N2F4 ______7. SCl2 ______8. NaMnO4 ______9. Sn(IO3)4 ______10. (NH4)2C2O4 ______11. Sr(BrO3)2 ______12. Hg2I2 ______13. HgI2 ______14. HIO3 ______15. H2SO3 ______16. barium hydroxide ______17. sodium hypochlorite ______18. lithium peroxide ______19. calcium hydride ______13 20. plumbic acetate ______21. ferrous chromate ______22. nickel(III)oxide ______23. zinc sulfite ______24. periodic acid ______25. lead(IV)chloride ______26. potassium hydrogen sulfate ______27. gallium arsenide ______28. hydrofluoric acid ______29. silicon dioxide ______30. magnesium selenide ______Text problems 74, 77, 78, 80, 83, 85, 8614

Brief History Leading to Atomic View of Matter

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