Geometric Structure and Localized Bonding Models

Geometric Structure and Localized Bonding Models
(also as attachment)

1. For each of the following chemical species: (i) write acceptable Lewis structures
(including major resonance contributors and indicating formal charges); (ii) designate
oxidation states for all atoms; and (iii) draw the stereochemical structures predicted by
VSEPR arguments, noting deviations from ideal bond angles and predicting the direction
of molecular dipoles.

a. ClOF3
b. [OTeF5]-
c. XeCl4
d. H2C=SF4 (indicate CH2 orientation)
e. BF3
f. N2O5

2. Polynitrogen species, [Nn]z (n > 2, z = charge), "are of significant interest as high energy
density materials (HEDM) for propulsion or explosive applications." The [N5]+[AsF6]-
salt, prepared in 1999, contains the first new polynitrogen species reported in over a
century. The compound is described as a "highly energetic, strongly oxidizing material
that can detonate violently. It should be handled only on a very small scale while using
appropriate safety precautions (face shields, leather gloves, and protective clothing)."

a. Write acceptable Lewis structures (including major resonance contributors and
formal charges) for the cation. What stereochemistry is predicted by the VSEPR
model? Are all N-N bonds the same length? Explain.

b. Only one other polynitrogen molecule is known. What is its trivial name? Give
its Lewis structure and geometry. Are all N-N bonds the same length? Where
might you find this molecule in daily life and in what application?

c. Theoretical chemists have explored the possible existence of other polynitrogen
species, including neutral molecules of composition N4. Write Lewis structures
for two different molecules with this composition. Why are they predicted to be
unstable?

d. There is only one stable polyoxygen species. What is its name, Lewis structure,
and geometry? What is the significance of this species?

3. White phosphorus, P4, is a reactive, molecular allotrope of phosphorus.

a. White phosphorus has no multiple bonds. Draw the Lewis-VSEPR structure for
this molecule.

b. What are the percentage s and p orbital contributions for hybrid orbitals that are
constructed to maximize overlap between the P-P bonds?

c. The hybrids in (b) are problematic. Why?

d. Assuming that phosphorus and hydrogens are of comparable electronegativity
(hence, comparable electron-donating/withdrawing capacity), do you expect the
phosphorus centers in white phosphorus to be more or less basic than the
phosphorus center in PH3? Explain.

4. Consider the trigonal planar NO2Cl molecule oriented against the coordinate system
shown at right:

a. Using the bond angles provided in the figure and the general properties of hybrid
orbitals, construct normalized hybrid orbitals for nitrogen that describe the σ-
framework in this system.

b. Demonstrate that the hybrid orbitals derived in part (a) are orthogonal to one
another.

c. Plot one of the oxygen-directed hybrids as a cross-section on the x-y plane.

d. Using two different theoretical models, predict how the structure of NO2F will
differ relative to the structure of NO2Cl.

Attachments

Solution Summary

A number of questions and answers regarding a number of aspects of chemical structure. Topics include stereochemistry, hybridization, lewis structures, VSEPR and molecular orbitals. A number of example structures are given.