1. 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

2. 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[
] -
= – = 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

3. 6.97
Determine the standard enthalpy of formation of ethanol (C2H5OH) from its standard enthalpy of combustion ( kJ/mol)
C2H5OH + 3O2 -> 2CO2 + 3H2O =
ΔH0
rxn
nΔH0 (products) f
Σ [
mΔH0 (reactants)] Σ[
] -
= [2(-393.5) + 3(-285.8)] – [3(0) + ΔHfoC2H5OH]
= – ΔHfoC2H5OH
ΔHfoC2H5OH = = kJ/mol
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4. 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
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5. Trends in First Ionization Energies
Generally, across a row, it gets harder to remove an electron because Zeff increases from left to right.
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6. Trends in First Ionization Energies
However, there are two apparent discontinuities in this trend.
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7. 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
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8. 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.
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9. General trend in first ionization energies
Increasing First Ionization Energy
Increasing First Ionization Energy
IE trends opposite of
size trends
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10. 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.
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11. Trends in Electron Affinity
In general, electron affinity becomes more exothermic as you go from left to right across a row.
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12. Trends in Electron Affinity
There are again, however, two discontinuities in this trend.
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13. 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.
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14. 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.
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15. 12/31/2018

16. 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.
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17. 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
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18. Comparisons are most valid when dealing with elements of the same type.
metals
nonmetals
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19. nonmetals, metalloids, metals
Greater variation in chemical properties even though similar electronic configurations
nonmetals, metalloids, metals
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20. Properties of Metals, Nonmetals, and Metalloids
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21. Metals versus Nonmetals
Differences between metals and nonmetals tend to revolve around these properties.
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22. Metals versus Nonmetals
Metals tend to form cations.
Nonmetals tend to form anions.
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23. Metals
Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.
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24. 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
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25. 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.
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26. 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.
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27. Metalloids Have some characteristics of metals, some of nonmetals.
For instance, silicon looks shiny, but is brittle and fairly poor thermal and electrical conductor.
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28. 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)
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29. Alkali Metals Soft, metallic solids.
Name comes from Arabic word for ashes.
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30. Alkali Metals Found only as compounds in nature.
Have low densities and melting points.
Also have low ionization energies.
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31. 2M(s) + 2H2O(l) 2MOH(aq) + H2(g)
Alkali Metals
Their reactions with water are famously exothermic. Li Na K
2M(s) + 2H2O(l) MOH(aq) + H2(g)
2H2(g) + O2(g) -> 2H2O(l)
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32. Group 1A elements (ns1, n  2)
M M+1 + 1e-
2M(s) + 2H2O(l) MOH(aq) + H2(g)
metal hydroxides
4M(s) + O2(g) M2O(s)
metal oxides
Increasing reactivity
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