Name Community College of Rhode Island Chemistry Department

Name______________________________________

Community College of Rhode Island
Chemistry Department
General Chemistry I
CHEM-1030-150

Hour Exam No. 4
Covering Chang Chapters 9 (partial), 10 and 11 (partial)

Thursday, December 4, 2014
Ten Questions, 50 Minutes, 100 Points
Closed book examination, No notes allowed
A periodic table is attached to the back of this exam

Answer all questions in the spaces provided.

1. For each pair of elements, state whether the binary compound they form is likely to be ionic or

covalent. Write the formula and name of each compound. (12 points)

O and Cl

Zn and I

S and F

2. Compare the observed characteristics (properties) of substances containing each type of
chemical bond: the ionic bond, the pure covalent bond and the polar covalent bond. (9 points)

2

3. Sketch and describe the dynamic equilibrium that exists in a closed system at constant

temperature consisting of a liquid and its vapor. (8 points)

4. The two common allotropic forms of carbon are graphite and diamond. Both allotropes have

extremely high melting points. Graphite soft and flaky and is used as a dry lubricant. Diamond

is the hardest substance known. Explain these facts based on their molecular structure and

bonding. (10 points)

3

5. Consider the three types of intermolecular forces, hydrogen bonding, dipole-dipole and

dispersion. Tell what type of boding is present in each of the eight substances listed below.

More than one type of bonding may be present in each substance. (One point will be

deducted for each wrong answer.) (15 points)

HCl CH2Cl2 CO

NH3 H2 CH4

O2 H2O2

6. Draw the Lewis structure of the PCl3 molecule. What is the hybridization state of P in

PCl3? What is the shape of the PCl3 molecule? Is the PCl3 molecule polar or nonpolar?

Explain how you reach your conclusion about the molecule’s polarity. (10 points)

4

7. Draw the Lewis structure of the SO3 molecule. What is the hybridization state of S in

SO3? What is the shape of the SO3 molecule? (8 points)

8. Draw the Lewis structure of the carbonate ion, CO32-. For one of its resonance structures,

calculate the formal charge on each atom and then calculate the average charge on each

oxygen atom. (8 points)

5

9. Starting with two hydrogen atoms, draw the molecular orbital diagram for the H2 molecule,

showing the bonding and nonbonding molecular orbitals. Show how you calculate the bond

order of the H2 molecule. (8 points)

10. Give a complete description of dispersion forces. Use words and a sketch to describe what

causes dispersion forces between molecules. (12 points)

6