Page 151 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:37 9in x 6in b985-appA Elementary Physical Chemistry

136 Elementary Physical Chemistry

3. Arrange in accordance with increasing or decreasing bond length:

+
+
−
(a) F , F 2, F ;(b) N , N 2,N .
−
2 2 2 2
Give reason(s) for your choice.
4. In the FEMO (free electron molecular orbital) theory of conjugation,
free electrons are treated as particles in a box. In butadiene there are
4 free electrons occupying the 2 lowest energy levels of the box. Taking
thesize of thebox to be560 × 10 −12 m, calculate the excitation energy
from the highest occupied level to the lowest unoccupied level.
35
5. The vibration–rotation spectrum of 1 H Cl has peaks at 2821.58,
2843.63, 2865.10, 2906.25, 2925.91, 2944.92cm −1 .Calculate
(a) the rotation constant B ,
∗
(b) the vibration frequency v .
∗
o
1
2
6. If the H in Problem 5 were replaced by H (deuterium), which molecule,
1 2
HCl or HCl, will have the greater
(a) vibration frequency,
(b) moment of inertia,
(c) rotational constant?
Explain.
7. The spacing between successive rotational lines in the far infrared of
35
1 H Cl is 20.5 cm −1 .Calculate
(a) the moment of inertia,
(b) the bond length.
8. What kind of intermolecular forces are present in the

(a) C H 6, (b) CHCl , (c) CH 3 COH?
2 3
9. The boiling points of several hydrogen-containing compounds increase
as follows:
H 2 S < H 2Se < H 2Te < H 2 O

Note that the heavier the molecule is, the higher the boiling temperature,
except for H 2O, which is the lightest of these substances. Explain.