CHM 134 General Chemistry I
Exam 3, Fall 2009 – Dr. Steel
1.
Name
(4 points) How many valence electrons does an atom of each of these elements have?
a) aluminum
b) sulfur
c) tin
d) titanium
2. (4 points) Label the bond that forms between the atoms in each of these pairs as either
ionic, polar covalent, pure covalent, or no bond.
a) carbon and oxygen
b) iodine and iodine
c) magnesium and chlorine
d) nitrogen and bromine
3. (6 points) From the list below, circle which molecules are linear.
BeI2
XeCl4
CO2
SO2
SCl2
XeF2
4. (6 points) From the list below, circle which molecules are polar.
H2O
PF5
NH3
SO2
PCl3
CS2
5. (2 points) Using periodic trends, place the following bonds in order of increasing ionic
character.
As-O
N-O
P-O
6. (6 points) From the list below, circle which atoms can expand their valence shell to
accommodate more than eight electrons.
S
Mg
N
F
Cl
Ne
7. (6 points) Based on the sketch provided, identify the VSEPR family to which each
structure belongs.
A
A
109.5 o
120o
X
A
90o
A
X
A
120o
A
X
A
A
A
A
A
A
8. (4 points) Circle all of the atoms in this structure that are sp2 hybridized.
O
H
H
H
C
C
C
N
O
H
H
H
9. (10 points) 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 NPO.
N
N
P
O
P
O
N
P
O
N
P
O
10. (6 points) Draw three distinct resonance structures of the perchlorate ion, ClO41-.
11. (6 points) Draw an appropriate Lewis dot structure for each molecule:
N2H2
SO3
12. (8 points) Consider the molecules below. Determine the total number of sigma and pi
bonds on each structure, respectively.
H
H
H
C1
C
H
C
H
sigma bonds
C
C2
C
NH2
pi bonds
O
H
H
O
H
C3
H
H
C
C4
N
sigma bonds
pi bonds
13. (6 points) Determine the enthalpy change for the following reaction based on the bond
energies included in the table.
H
H
H
C
C
H
H
H
+
Cl
Cl
H
H
H
C
C
H
H
Cl +
H
Cl
Bond
Bond Energy (kJ/mol)
H-H
436
C-H
414
H-Cl
431
C=C
611
C-Cl
339
Cl-Cl
243
14. (18 points) Complete the table below by drawing a Lewis Dot structure for each species,
providing a 3D sketch of the species that includes estimated bond angles, naming the
molecular geometry of the species, and identifying the type of orbital hybridization
present on the central atom of the species.
Molecule
BrF3
H3O1+
IF41-
Lewis Structure
Sketch
(with angles)
Geometry
Hybridization
on central atom
Use the molecular orbital diagrams shown to answer the questions below.
N21-
O2
15. (2 points) What is the bond order of the O2 molecule?
16. (2 points) What is the bond order of the N21- ion?
17. (4 points) Circle any species in the group below that will be paramagnetic.
O22+
O21+
O2
O22-
N22+
N21+
N2
N22-