Spring Chemistry Homework #5 Answer Key

Introduction to Quantum Chemistry

Oxtoby, Nachtrieb and Gillis: Chapter 15:
 

46. Electron configurations of neutral atoms:

a) P: [Ne] 3s² 3p³

b) Tc: [Kr] 4d⁵ 5s²

c) Ho: [Xe] 4f¹¹ 6s²

48. Electron configurations of ions:

a) Li^-: [He] 2s²

b) B⁺: [He] 2s²

c) F^-: [He] 2s² 2p⁶ = [Ne]

d) Al³⁺: [Ne]

e) S^-: [Ne] 3s² 3p⁴

f) Ar⁺: [Ne] 3s² 3p⁵

g) Br⁺: [Ar] 3d¹⁰ 4s² 4p⁴

h) Te^-: [Kr] 4d¹⁰ 5s² 5p⁵

The following ions will have unpaired electrons: S^-, Ar⁺, Br⁺, and Te^-.

50.

a) the neutral atom with this electron configuration is osmium (Os).

b) F^-

c) Ag⁵⁺ (ouch! this is a very high oxidation state for silver)
 

54. If the allowed values of ms were -½, 0 and ½, the Pauli Exclusion Principle would then allow three electrons in a given orbital. Therefore, the first three noble gases (that is, the first three atoms with filled valence shells) would have the following electron configurations:

First Noble Gas: 1s³ (Z = 3)

Second Noble Gas: 1s³ 2s³ 2p⁹ (Z = 15)

Third Noble Gas: 1s³ 2s³ 2p⁹ 3s³ 3p⁹ (Z = 27)

60. Higher Ionization Energies:

a) Bi vs. Xe: xenon should have the higher ionization energy its outermost electrons are not as well shielded from the nuclear charge (it is to the right of bismuth) and are closer to the nucleus (the highest occupied atomic orbitals have a smaller principle quantum number (it is above bismuth).

b) Se vs. Te: selenium will have the higher ionization since its valence electrons are in orbitals with a lower principle quantum number (it is directly below tellurium on the Periodic Table).

c) Rb vs. Y: yttrium will have the higher ionization energy since its outermost electrons are exposed to a greater nuclear charge and are not well shielded (i.e., it is directly to the right of rubidium).

d) K vs. Ne: neon would have the higher ionization by far since its outermost electrons are very poorly shielded (it is to the right) and occupy an orbital with a smaller n quantum number.

a) Rb or Sr: rubidium will have the higher electron affinity since the added electron in strontium will occupy a higher energy orbital (the 4d orbital) than the highest energy orbital in the neutral atom (the 5s orbital). In rubidium, the added electron will occupy an orbital that has the same energy as the highest energy orbital (5s) in the neutral atom.

b) I or Rn: iodine will have the larger electron affinity since the added electron in radon will occupy a higher energy orbital (the 7s orbital) than the highest energy orbital in the neutral atom (the 6p orbital). In iodine, the added electron will occupy an orbital that has the same energy as the highest energy orbital (5p) in the neutral atom.

c) Ba or Te: tellurium will have the higher electron affinity since the added electron will occupy an orbital that has the same energy as the highest energy orbital (5p) in the neutral atom. In the case of barium, the added electron must go in a higher energy orbital.

d) Bi or Cl: chlorine will have the highest electron affinity (it has the highest of any element) since the added electron will be poorly shielded from the nuclear charge. In the case of bismuth, the added electron will be destabilized by the pairing energy required to have two electrons in the same orbital. It will also be lower since the orbital energy involved is higher than that involved with chlorine.

83. Cr⁴⁺ will have the electron configuration: [Ar] 3d². It will have two unpaired electrons. Note that in transition metal ions, the 4s orbital is higher than the 3d (the reverse of the order seen for the neutral elements), so the 4s electrons that are present in the neutral atom are removed first.
 

DeKock & Gray: Chapter 2:

3. To explain why silicon and sulfur have higher electron affinities than phosphorus, it is helpful to look at the electron configurations of these atoms.
 
 
 

 
The added electron in silicon will occupy a vacant 3p orbital. The added electron in phosphorus will occupy an already half-filled 3p orbital so it will be destabilized by the pairing energy. This is be partially offset by the increased nuclear charge however. The added electron in sulfur will also occupy an already half-filled orbital, like phosphorus, but relative to phosphorus, sulfur has a higher nuclear charge.