Chemistry 181H
Problem Set #8, 25 October 2005 and 27 October 2005
1. (Problem 9 from Problem Set #7) Write Lewis structures for NCO- and CNO-. Compare the
shapes and dipole moments of these molecules with those of the isoelectronic molecule CO2.
Sketch the shapes expected for each molecule, and indicate the direction of the dipole
moment.
2. For Problem Set #7, you wrote Lewis structures for BF3, NO3-, and NF3 and then applied
VSEPR theory to predict molecular shapes and bond angles. Use these results to predict the
magnitude (zero or nonzero) and direction of the dipole moments for these molecules.
3. Write Lewis structures for XeF4, SbF5, XeO4, and XeOF2. Identify and sketch the shapes
predicted for these molecules using VSEPR theory. Include bond angles on the sketch. Which
of these molecules are polar? Show the direction of the dipole moment on the sketches of the
polar molecules.
4. Draw Lewis structure(s) for the ozone molecule O3, and then use VSEPR to predict its
molecular shape.
5. Consider the reactions given on the lecture slide entitled “Ozone Destruction by
Chlorofluorocarbons (CFCs).” Identify the species with unpaired electrons (free radicals).
Note that all of the electrons are typically paired in molecules with even numbers of electrons.
However, O2, which is paramagnetic, is an important exception.
6. The molecule chlorine nitrate ClONO2 is a reservoir species that sequesters the species ClO,
which participates in the catalytic destruction of ozone. Chlorine nitrate is formed by the
reaction
ClO(g) + NO2(g) → ClONO2(g)
Draw Lewis structures for the participants in this reaction and predict their shapes. Which of
these molecules are polar? Explain
7. Identify the following compounds as Lewis acids or bases: BCl3, H2O, Zn2+, HCN, and SF4.
Use Lewis structures to justify your responses.
8. Write Lewis structures for the reactants and the resulting Lewis acid-base complex formed as
a product in each of the reactions given below. Identify the reactant that acts as a Lewis acid
and the one that behaves as a Lewis base. Determine the shape of the product for each
reaction, and predict its bond angles.
a. PCl4+ + Cl- →
b. Cu2+ + 6 NH3 →
9. For the pairs of compounds given below, identify the compound which is a stronger Lewis
base. Justify your choices.
a. BF3 or BH3
b. NH3 or H2O
c. AsH3 or NH3