1.
(2012) Answer the following questions in terms of principles of chemical bonding and intermolecular forces. In each explanation where a comparison is to be made, a complete answer must include a discussion of both substances. The following complete Lewis electrondot diagrams may be useful in answering parts of this question. d. a. b. c. e.
At 1 atm and 298 K, pentane is a liquid whereas propane is a gas. Explain.
At 1 atm and 298 K, methanol is a liquid whereas propane is a gas. Explain.
Indicate the hybridization of the carbon atom in each of the following: i. ii.
Methanol
Methanoic (formic) acid
Draw the complete Lewis electron-dot diagram for a molecule of propanoic acid,
HC
3
H
5
O
2
.
Explain the following observations about the two carbon-oxygen bonds in the methanoate (formate) anion, HCO
2
. You may draw a Lewis electron-dot diagram (or diagrams) of the methanoate ion as part of your explanations. i. The two carbon-oxygen bonds in the methanoate (formate) anion, HCO
2
, have the same length. ii. The length of the carbon-oxygen bonds in the methanoate (formate) anion,
HCO
2
, is intermediate between the length of the carbon-oxygen bond in methanol and the length of the carbon-oxygen bond in methanal.

2. (2006) Answer each of the following in terms of principles of molecular behavior and chemical concepts.
(a) The structures for glucose, C
6
H
12
O
6
, and cyclohexane, C
6
H
14
, are shown below.
Identify the type(s) of intermolecular attractive forces in
(i) pure glucose
(ii) pure cyclohexane
(b) Glucose is soluble in water but cyclohexane is not soluble in water. Explain.

3. (2003) Using the information in the table, answer the following questions about organic compounds.
Compound Name Compound Formula ΔH vap o (kJ mol -1 )
Propane
Propanone
1-propanol b.
CH
3
CH
2
CH
3
CH
3
COCH
3
CH
3
CH
2
CH
2
OH
19.0
32.0
47.3
For each pair of compounds below, explain why they do not have the same value for their standard heat of vaporization, ΔH vap o . (You must include specific information about both compounds in each pair.) i. ii. propane and propanone propanone and 1-propanol
d. Given the structural formula for propyne below, i. ii. indicate the hybridization of the carbon atom indicated by the arrow in the structure above; indicate the total number of sigma (σ) bonds and the total number of pi (π) bonds in the molecule.

a) d)
4 (2004) Use appropriate chemical principles to account for each of the following observations. In each part, your response must include specific information about both substances.
At 25 o C and 1 atm, F
Ammonia, NH
3
2
is a gas, whereas I
2
is a solid.
, is very soluble in water, whereas phosphine, PH
3
, is only moderately soluble in water.
In the diagram above, which of the labeled arrows identifies hyrogen bonding in water?
A.
A
B.
B
C.
C
D.
D

The diagram above shows molecules of Bromine and iodine drawn to the same scale. Which of the following is the best explanation for the difference in the boiling points of liquid bromine and iodine, which are 59⁰C and 184⁰C, respectively. a.
Solid iodine is a network covalent solid, whereas solid bromine is a molecular solid b.
The covalent bonds in iodine molecules are weaker than those in bromine molecules c.
Iodine molecules have electron clouds that are more polarizable than those of bromine molecules, thus London dispersion forces are stronger in liquid iodine d.
Bromine has a greater electronegativity than iodine, thus there are stronger dipole-dipole forces in liquid bromine than in liquid iodine.

Consider the molecules represented above and the data in the table below
Nonane and 2,3,4-triflouropentane have almost identical molar masses, but nonane has a significantly higher boiling point, which of the following statements best helps explain this observation. a.
The C-F bond is easier to break than the C-H bond b.
The C-F bond is more polar than the C-H bond c.
The carbon chains are longer in nonane are in 2,3,4-trifoluropentane d.
The carbon chains are farther apart in a sample of nonane than they are in 2,3,4-trifluropentane
The figure above shows that in solid hydrogen fluoride there are two different distances between H atoms and F atoms. Which of the following best accounts for the two different distances? a.
Accommodation of the necessary bond angles in the formation of the solid b.
Difference in strength between covalent bonds and intermolecular attractions c.
Different isotopes of fluorine present in the sample d.
Uneven repulsions among nonbonding electron pairs