CHM134 General Chemistry I
Exam 3, Fall 2010
Name
1. Draw a reasonable Lewis Dot Structure for each of these species. Show all valence
electrons. None of these require you to violate the octet rule. (12 points)
SBr2
NO21-
PCl3
N2H4
2. Draw a reasonable Lewis Dot Structure for each of these species. Show all valence
electrons. Each of these requires you to violate the octet rule. (9 points)
ClF5
PCl5
BF3
3. Draw three non-equivalent resonance structures for the bromite ion, BrO21-. Each structure
has the bromine atom in the center. (6 points)
4. Based on the Lewis Structures provided, complete the table below by providing a sketch of
the species (in 3-D, if appropriate), supplying the idealized bond angles, naming the
molecular geometry of the species, identifying the type of orbital hybridization present on the
central atom of the species, and indicating whether the species is polar or nonpolar.
(20 points)
Molecule
SO2
SeBr4
NH3
SiF4
Lewis
Structure
Sketch
(with angles)
Geometry
Hybridization
on central
atom
Polarity
5. Determine whether a bond between each of the following pairs of atoms would be nonpolar
covalent, polar covalent, or ionic. (4 points)
Li and O
C and O
N and S
Cl and Cl
6. Assign formal charges to the elements in each of the structures below. Based on your
assigned formal charges, circle the structure that makes the greatest contribution to the
correct structure of the species. (7 points)
H
H
C
H
S
H
S
C
H
C
S
7. Use bond energies from the table provided to determine the enthalpy change for the
following reaction. (8 points)
O
O
N
O
+ 4 H2
N
O
N2 + 4 H2O
8. Consider the structures of caffeine (left) and vitamin C (right) below in order to answer the
questions that follow. (3 points each, 15 points total)
a. How many sigma (σ) bonds are present in the vitamin C structure?
b. How many pi (π) bonds are present in the caffeine structure?
c. How many sp2 hybridized carbon atoms are present in the caffeine structure?
d. How many sp3 hybridized oxygen atoms are present in the vitamin C structure?
e.
How many sp2 hybridized nitrogen atoms are present in the caffeine structure?
9. For each of the pairs of orbitals shown below, considering their types and orientation, what
type of bond is the most likely to form? (4 points)
Use the following molecular orbital diagram to help answer the remaining questions.
(10 – 12 are worth 3 points each; 13 – 15 are worth 2 points each)
10. According to molecular orbital theory, what is the bond order in the oxygen molecule?
11. According to molecular orbital theory, is the oxygen molecule diamagnetic or paramagnetic?
12. According to molecular orbital theory, what is the bond order in the F21- ion?
13. According to molecular orbital theory, which species below is least likely to exist?
F22+
F2
F22-
14. According to molecular orbital theory, which of these species has the longest bond length?
O22+
O2
O22-
15. According to molecular orbital theory, which of these species will be attracted to a magnetic
field?
F22+
F2
F22-