CHM134 General Chemistry I
Examination 4, Fall 2008 – Dr. Steel
Name
1. Calculate the heat transferred in the following reaction (ΔHrxn). Indicate which
direction (exothermic or endothermic) the heat is transferred. (5 points)
H
H Cl
Cl
+
C C
Cl
F
F
F C C H
H
Cl F
2. Assign formal charges to the elements in each of the structures below and enter the
results in the boxes below each structure. Based on your assigned formal charges,
circle the structure that makes the greatest contribution to the correct structure of
CNO-. (10 points)
A
B
C
Formal Charge
C
N
O
3. Draw a Lewis structure for CH3CN that obeys the octet rule for all atoms. Include
resonance forms if necessary. (5 points)
4. Draw two non-equivalent Lewis structures for BrO3-. Based on your structures,
which makes the greatest contribution to the correct structure of BrO3-? (5 points)
5. In the first column, draw a Lewis Dot structure for each species. In the second
column, provide a 3D sketch of the species that includes estimated bond angles and
the name of the shape. (24 points)
LEWIS DOT STRUCTURE
CH4 (example)
VSEPR Sketch
H
H
109.5 o
H
C
H
C
H
H
H
H
shape name:
NH3
shape name:
CO2
shape name:
SF4
shape name:
BF3
shape name:
tetrahedral
6. From the list below, circle which molecules are linear. (6 points)
H2O
XeCl2
CS2
SO2
BeCl2
CH4
7. From the list below, circle which molecules are polar (having a non-zero dipole
moment). (6 points)
CH4
H2O
SF4
PCl5
SF6
NCl3
8. Using periodic trends, place the following bonds in order of increasing ionic
character. (2 points)
S-F
Se-F O-F
9. From the list below, circle which molecules contain pure covalent bonds. (6 points)
NaCl
PF3
Cl2
H2O
H2
LiH
10. From the list below, circle which atoms can form compounds with expanded octets.
(6 points)
N
Be
S
Br
O
He
11. Consider the molecule below. Determine the hybridization at each of the numbered
carbons. Also, indicate the total number of sigma and pi bonds on the structure,
respectively. (8 points)
C2
C1
sigma bonds
pi bonds
12. A molecule whose center has sp3d2 hybridization falls into which electron pair
geometry family? (2 points)
Use the molecular orbital diagram shown to answer the questions below.
13. What is the bond order of the O22+ ion? (3 points)
14. Circle any species that will be diamagnetic. (5 points)
O22+
O21+
O2
O21-
O22-
15. What is the bond order of the F2 molecule? (3 points)
16. For the series of species below, which has the shortest bond length and which has the
longest bond length? (4 points)
F22+
F21+
F2
F21-