No class on Monday, March 20 Midterm is Friday, March 24 Important notes! No class on Monday, March 20 Midterm is Friday, March 24 12/31/2018

7.107 Ozone (O3) in the stratosphere absorbs the harmful radiation from the sun by undergoing decomposition: O3 -> O + O2. (a) Referring to Table 6.4, calculate the ΔHo for this process. (b) Calculate the maximum wavelength of photons (in nm) that possess this energy to cause the decomposition of ozone photochemically. = ΔH0 rxn nΔH0 (products) f Σ [ mΔH0 (reactants)] Σ[ ] - = 249.4 – 142.2 = 107.2 kJ/mol 1.072x105 J/mol x (1 mol/6.022x1023 photons) = 1.781x10-19 J/photon E=hc/λ so λ=hc/E = [(6.63x10-34 Js)*(3.00x1017 nm s-1)]/1.781x10-19 J = 1117 nm 12/31/2018

6.97 Determine the standard enthalpy of formation of ethanol (C2H5OH) from its standard enthalpy of combustion (-1367.4 kJ/mol) C2H5OH + 3O2 -> 2CO2 + 3H2O = ΔH0 rxn nΔH0 (products) f Σ [ mΔH0 (reactants)] Σ[ ] - -1367.4 = [2(-393.5) + 3(-285.8)] – [3(0) + ΔHfoC2H5OH] -1367.4 = -1644.4 – ΔHfoC2H5OH ΔHfoC2H5OH = -1644.4 + 1367.4 = -277.0 kJ/mol 12/31/2018

Isoelectronic comparisons In an isoelectronic series, ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge 8 9 11 12 13 12/31/2018

Trends in First Ionization Energies Generally, across a row, it gets harder to remove an electron because Zeff increases from left to right. 12/31/2018

Trends in First Ionization Energies However, there are two apparent discontinuities in this trend. 12/31/2018

Trends in First Ionization Energies The first occurs between Groups IIA and IIIA Electron removed from p-orbital rather than s-orbital Electron farther from nucleus Small amount of repulsion by s electrons 12/31/2018

Trends in First Ionization Energies The second occurs between Groups VA and VIA. Electron removed comes from doubly occupied orbital. Repulsion from other electron in orbital helps in its removal. 12/31/2018

General trend in first ionization energies Increasing First Ionization Energy Increasing First Ionization Energy IE trends opposite of size trends 12/31/2018

Electron affinity is the potential energy change associated with the addition of an electron to an atom in the gaseous state to form an anion. X (g) + e- X-(g) F (g) + e- F-(g) ΔH = -328 kJ/mol EA = +328 kJ/mol O (g) + e- O-(g) ΔH = -141 kJ/mol EA = +141 kJ/mol For nearly all atoms (except group 2A and 8A), the addition of 1 electron is exothermic. Some textbooks (yours) report EA values as –ΔH (i.e., positive values). Others report them as ΔH. Removal of electrons (ionization energies) are endothermic. 12/31/2018

Trends in Electron Affinity In general, electron affinity becomes more exothermic as you go from left to right across a row. 12/31/2018

Trends in Electron Affinity There are again, however, two discontinuities in this trend. 12/31/2018

Trends in Electron Affinity The first occurs between Groups IA and IIA. Added electron must go in p-orbital, not s-orbital. Electron is farther from nucleus and feels repulsion from s-electrons. 12/31/2018

Trends in Electron Affinity The second occurs between Groups IVA and VA. Group VA has no empty orbitals. Extra electron must go into occupied orbital, creating repulsion. 12/31/2018

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Variation in chemical properties of representative elements IE & EA help chemists understand the types of rxns that elements undergo and the nature of the elements’ compounds. IE indexes the attraction of an atom for its own electrons. EA indexes the attraction of an atom for additional electrons (from some other source). Metallic character increases going left and down. 12/31/2018

closeness of charge density (charge/volume) of their cations First member of a group will differ slight from the rest of the members and resemble its diagonal element. closeness of charge density (charge/volume) of their cations 12/31/2018

Comparisons are most valid when dealing with elements of the same type. metals nonmetals 12/31/2018

nonmetals, metalloids, metals Greater variation in chemical properties even though similar electronic configurations nonmetals, metalloids, metals 12/31/2018

Properties of Metals, Nonmetals, and Metalloids 12/31/2018

Metals versus Nonmetals Differences between metals and nonmetals tend to revolve around these properties. 12/31/2018

Metals versus Nonmetals Metals tend to form cations. Nonmetals tend to form anions. 12/31/2018

Metals Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity. 12/31/2018

Metals Compounds formed between metals and nonmetals tend to be ionic. Metal oxides tend to be basic (react with acids, or produce bases when dissolved in H2O). NiO is insoluble in H2O, but reacts with HNO3 to give a green solution of the salt Ni(NO3)2 12/31/2018

Nonmetals Dull, brittle substances that are poor conductors of heat and electricity. Tend to gain electrons in reactions with metals to acquire noble gas configuration. white phosphorus sulfur C (graphite) iodine Nonmetals vary greatly in appearance. 12/31/2018

Nonmetals Substances containing only nonmetals are molecular compounds. Most nonmetal oxides are acidic (react with bases, produce acids when dissolved in H2O). CO2 (nonmetal oxide) dissolves in H2O to produce H2CO3 (an acid). Indicator is blue in basic solution and yellow in acidic solution. 12/31/2018

Metalloids Have some characteristics of metals, some of nonmetals. For instance, silicon looks shiny, but is brittle and fairly poor thermal and electrical conductor. 12/31/2018

No good place for hydrogen (1s1) Even though in Group 1A, is not a metal Nonmetal, occurs as colorless diatomic gas Forms molecular compounds with other nonmetals Forms both H+ (proton, hydronium ion) in aqueous solution Forms H- (hydride) with active metals Metal hydrides react with H2O to form H2 gas and the corresponding metal hydroxides 2NaH(s) + 2H2O(l) -> 2NaOH(aq) + H2(g) CaH2(s) + 2H2O(l) -> Ca(OH)2(s) + 2H2(g) 2H2(g) + O2(g) -> 2H2O(l) 12/31/2018

Alkali Metals Soft, metallic solids. Name comes from Arabic word for ashes. 12/31/2018

Alkali Metals Found only as compounds in nature. Have low densities and melting points. Also have low ionization energies. 12/31/2018

2M(s) + 2H2O(l) 2MOH(aq) + H2(g) Alkali Metals Their reactions with water are famously exothermic. Li Na K 2M(s) + 2H2O(l) 2MOH(aq) + H2(g) 2H2(g) + O2(g) -> 2H2O(l) 12/31/2018

Group 1A elements (ns1, n  2) M M+1 + 1e- 2M(s) + 2H2O(l) 2MOH(aq) + H2(g) metal hydroxides 4M(s) + O2(g) 2M2O(s) metal oxides Increasing reactivity 12/31/2018