Matter & Motion

Chemistry Homework #8

Classical Bonding and Intermolecular Forces

Oxtoby, Nachtrieb & Gillis - Chapter 3
 

42.
 
compound
lone pairs 
on central atom
steric 
number
electron pair 
geometry
molecular 
geometry
PF3
1
4
tetrahedral
pyramidal
SO2Cl2
0
4
tetrahedral
tetrahedral
PF6-
0
6
octahedral
octahedral
ClO2-
2
4
tetrahedral
angular
GeH4
0
4
tetrahedral
tetrahedral

 

44.
 
compound
lone pairs 
on central atom
steric 
number
electron pair 
geometry
molecular 
geometry
polarity
TeH2
2
4
tetrahedral
tetrahedral*
polar
AsF3
1
4
tetrahedral
pyramidal**
polar
PCl4+
0
4
tetrahedral
tetrahedral
non-polar
XeF5+
1
6
octahedral
square pyramidal†
polar

* The bond angle of TeH2 is expected to be less than the ideal 109.5º due to repulsion from the non-bonding pairs.

** The bond angles of AsF3 are expected to be less than the ideal 109.5º.

† The four fluorine atoms that form the "base" of the pyramid are expected to be pushed toward the apex fluorine due to repulsion from the lone pair.
 

Oxtoby, Nachtrieb & Gillis - Chapter 5
 

16: The most important attractive forces acting between the following species are:

a) Ne: London dispersion forces (induced dipole/ induced dipole attractions)
b) ClF: dipole-dipole attractions
c) F2: London dispersion forces
d) BaCl2: ionic attractions
18. An atom of argon will be more attracted to an atom of krypton since krypton's electron cloud is more polarizable, and therefore susceptible to an induced dipole, than either argon or neon.

22. In this series, IF5 is expected to be the solid, BrF5 is expected to be the liquid and ClF5 is expected to be the gas. Not only would the polarizability be greater for IF5 (resulting in larger London dispersion forces), but the dipole moment will be the largest for this molecule since the difference in electronegativity is greatest for the I-F bond. This will result in stronger dipole-dipole attractions.

24. Order of boiling points:
 
order of boiling point compound dominant intermolecular force
(1) lowest He London dispersion
(2) Ar London dispersion (Ar is more polarizable than He)
(3) SO2 dipole-dipole attractions
(4) HF hydrogen bonding
(5) highest CaF2 ionic attractions

28. H2O2 is capable of hydrogen bonding since there is hydrogen bonded to oxygen, and the oxygen has lone pairs available to "bond" to hydrogen atoms on other molecules. It should therefore have a higher boiling point than either F2, which has only London dispersion forces, or H2S, which will have relatively weak dipole-dipole attractions.
 

DeKock and Gray - Chapter 2

38.
 
desired geometry
steric number
required
lone pairs on tellurium required
example
a) angular
4
2
TeF2
b) T-shaped
5
2
TeF3-
c) pyramidal
4
1
TeF3+
d) seesaw
5
1
TeF4
e) square planar
6
2
TeF42-
f) square pyramidal
6
1
TeF5-
g) trigonal bipyramidal
5
0
TeF5+
h) octahedral
6
0
TeF6

40. XeF5+ is a perfectly reasonable species. The central xenon would have an oxidation state of +6, meaning it would have one lone pair. As such it would have steric number of six and would have perfect square pyramidal geometry.
 

43. The difference in electronegativity between oxygen and hydrogen (Dc = 1.24) is greater than that for oxygen and fluorine (Dc = 0.54), resulting in greater dipole moments for the individual bonds. Moreover, the electron pairs on the oxygen atom in OF2 will partially offset the dipole in the direction of the fluorine atoms. In the case of water, the lone pairs on oxygen are directed in the same direction as the bond dipoles, enhancing the overall dipole moment of the molecule.