CHM 134 General Chemistry I
Exam 4, Spring 2010
Name
Table of Electronegativities 1. 4 pts. Describe the bond that would form between each of the following pairs of atoms as
being ionic, polar covalent, or purely covalent:
H O
_______________
Cl
Cl
_______________
Li O
_______________
C
F
_______________
2. 5 pts. Arrange the following bonds in order of increasing polarity: P-S P-N P-Si P-I P-B
>
>
>
>
3. 4 pts. How many valence electrons are present in each of these neutral atoms?
O ___
Sc
P ____
H
4. 8 pts. Assign formal charges to all the atoms in the following and place these next to the atom.
Which structure has the most favorable formal charges (circle one).
F
O
O
O
C
C
C
Cl
F
Cl
F
Cl
5. 6 pts. From the list below, circle which molecules are linear.
BeCl2
XeCl2
SCl2
CO2
H2O
OF2
6. 6 pts. From the list below, circle which molecules are planar (flat, all atoms in a plane).
BrF5
XeF4
CH4
BCl3
NH3
SF6
PCl3
BCl3
7. 6 pts. From the list below, circle which molecules are polar.
H2O
BrF3
CCl4
SO2
8. 12 pts. Draw an appropriate Lewis dot structure for each of these. If an atom can expand its
octet to produce better formal charges, go ahead and do that. Otherwise, make sure that the
octet rule is obeyed for all non-hydrogen atoms. Use resonance wherever needed.
HCCH
NNO
OBrO-
I3 -
9.
8 pts. Consider the molecule below. Complete the Lewis Diagram by adding electron dots
where appropriate (do not add additional bonds). Determine the total number of sigma and pi
bonds on the structure.
N
Cl
C
C
C
# sigma (σ) bonds
O
O
C
C
H
C
H
# pi (π) bonds
H
H
H
H
10. 6 pts. Determine ΔH for the following reaction based on the bond energies provided. Also
indicate if the heat is consumed or released.
F
O
+
C
H
H
H
F
H
C
O
H
H
11. 25 pts. Fill in each of the empty cells of this table:
example
Lewis structure
electron pair geometry
VSEPR sketch
molecular geometry including approximate
angles
hybridization
180
BeI2
I
CF3+
bent
sp3
SiH4
PCl5
I
trigonal planar
PO2-
ClH2+
Be
H
Cl
H
12. 10 pts. Use MO theory to predict the bond order and magnetism of each molecule:
molecule bond order magnetism (circle one)
B22-
diamagnetic or paramagnetic
C22+
diamagnetic or paramagnetic
N2
diamagnetic or paramagnetic
O2
diamagnetic or paramagnetic
F2
diamagnetic or paramagnetic