1
Name______________________________________
Inorganic Chemistry 411/511
Midterm Exam # 1
60 minutes
Partial credit is given, please show all your work. A periodic table is on the last page if needed.
1.
For the following: [8 pts each]
(i) give a Lewis structure, (ii) draw the species and write the correct geometry and (iii)
indicate expected deviations (if any) from ideal VSEPR coordination angles, or write “no
deviations” if you expect ideal bond angles.
a.
SeO32-
trigonal pyramidal with <O-Se-O less than 109.5°
b.
IF6+
regular octahedron
2a.
Construct an MO diagram for nitric oxide (NO). Show atomic and molecular orbital
levels with appropriate energies and symmetry labels, and indicate the electron filling.
[10 pts]
See Fig 2.22 in the text for a very similar MO. For NO, there are 11 valence electrons,
so the configuration is 1σ22σ21π43σ22π1
2b.
Draw a picture of the πg molecular orbital in NO. [6 pts]
See Fig. 2.23 in text (the 2π figure). Since this is an antibonding orbital, the larger lobes
are on the less electronegative atom (N).
2
2c.
Does NO or NO+ have a stronger bond? Which bond is longer? Explain. [8 pts]
The electron is being removed from an antibonding orbital, so NO+ has a shorter,
stronger bond than NO. The bond order increases from 2.5 to 3 when the electron is
removed.
3a.
Give a Born-Haber analysis of ΔHf of aluminum nitride, AlN(s). You do not need to use
numeric values, just write the discrete steps, and label each with an energy term such as
ionization energy (I), or electron affinity (Ea) , or bond enthalpy (D0) , etc. Be sure to
clearly indicate the sign (+ or -) of each term. Equations and energy terms should
correctly show the reaction stoichiometry. [16 pts]
Al(s) → Al(g)
Al(g) → Al(g)3+ + 3e½ N2(g) → N(g)
N(g) + 3e- → N3-(g)
Al(g)3+ + N3-(g) → AlN(s)
Al(s) + ½ N2(g) → AlN(s)
3b.
ΔHat (Al)
I1(Al) + I2(Al) + I3(Al)
½ D0(N2)
- Ea1(N) - Ea2(N) - Ea3(N)
-ΔHL(AlN)
ΔHf(AlN)
Does the Gibbs free energy in reaction 3a become more favorable at higher temperature?
Explain using the relationship between free energy, enthalpy, and entropy. [8 pts]
Less favorable. ΔS is negative for the reaction because gas is consumed to form only
solid. Hence, -TΔS is positive, and ΔG will increase as the temperature rises.
4a.
Sketch and describe in writing a unit cell for the fluorite structure. [12 pts]
CaF2 is a close packed anion array with Ca2+ ions in all Td sites. See Fig 3.37 or the
lecture notes.
5.
Answer every question; there is no deduction for incorrect answers. [4 pts each]
i.
If the energy of an electron in a ground-state H = –E, what is the ionization energy of
ground-state He+(g)?
(a) 4E
(b) E/4
(c) 3E/16
(d) 0
(e) E/16
(f) E/8
3
ii.
What is the stacking sequence of hexagonal 2D layers in the sphalerite structure? Capital
letters are anion layers, lowercase are cation layers.
(a) (AaBbCc)n
(d) (AcBaCb)n
(b) (ABCabc)n
(e) (AcB)n
(c) (AbABaB)n
(f) (AaBb)n
iii.
How many unpaired electrons in the ground state of V2+(g)?
(a) 0
(b) 1
(c) 2
(d) 3
(e) 4
iv.
v.
Which of the following has the smallest lattice enthalpy?
(a) LiF
(b) CaO
(c) NaCl
(d) AlN
(e) NiO
What is the cation and anion coordination in the ReO3 structure?
(a) (1, 3)
(b) (3, 1)
(c) (4, 4)
(d) (1, 1)
(e) (6, 2)
(f) (12, 6)
(f) 5
(f) CsI
4
5
vi.
Which is not linear?
(a) CO2
(b) ICl2-
(c) XeF2
(d) SO2
(e) BeH2
(f) CO