Chapter 9

Draw Lewis structures for the following and use the geometry predicted by the VSEPR model to determine what kind of hybrid orbitals the central atom uses in bond formation: (a) \(\mathrm{ClO}_{3}^{-},(\mathbf{b}) \mathrm{SO}_{3},\) and \((\mathbf{c}) \mathrm{OF}_{2}\).

Use the VSEPR model to help you describe the bonding in the following molecules according to VB theory: (a) arsenic trichloride and (b) chlorine trifluoride. Use orbital diagrams for the central atom to show how hybridization occurs.

Construct the molecular orbital diagram for \(\mathrm{O}_{2} .\) What is the net bond order in \(\mathrm{O}_{2} ?\)

Construct the molecular orbital diagram for \(\mathrm{N}_{2} .\) What is the new bond order in \(\mathrm{N}_{2}\) ?

Assume that in the \(\mathrm{NO}\) molecule the molecular orbital energy level sequence is similar to that for \(\mathrm{O}_{2}\). What happens to the NO bond length when an electron is removed from \(\mathrm{NO}\) to give \(\mathrm{NO}^{+} ?\) How would the bond energy of NO compare to that of \(\mathrm{NO}^{+}\) ?

Assume that in the \(\mathrm{NO}\) molecule the molecular orbital energy level sequence is similar to that for \(\mathrm{O}_{2}\). What happens to the NO bond length when an electron is added to \(\mathrm{NO}\) to give \(\mathrm{NO}^{-} ?\) How would the bond energy of \(\mathrm{NO}\) compare to that of \(\mathrm{NO}^{-} ?\)

Which of the following molecules or ions are paramagnetic? (a) \(\mathrm{O}_{2}^{+},(\mathbf{b}) \mathrm{O}_{2},(\mathbf{c}) \mathrm{O}_{2}^{-},(\mathbf{d}) \mathrm{NO},\) (e) \(\mathrm{N}_{2}\)

Which of the following molecules or ions are paramagnetic? (a) \(\mathrm{B}_{2},(\mathbf{b}) \mathrm{C}_{2},(\mathbf{c}) \mathrm{C}_{2}^{-},(\mathbf{d}) \mathrm{C}_{2}^{2-},(\mathrm{e}) \mathrm{F}_{2}\).

Construct the MO energy level diagram for the OH molecule assuming it is similar to that for HF. How many electrons are in (a) bonding MOs and (b) nonbonding MOs? What is the net bond order in the molecule?

Formaldehyde has the Lewis structure What would you predict its shape to be?

Antimony forms a compound with hydrogen that is called stibine. Its formula is \(\mathrm{SbH}_{3}\) and the \(\mathrm{H}-\mathrm{Sb}-\mathrm{H}\) bond angles are \(91.3^{\circ} .\) Which kinds of orbitals does \(S b\) most likely use to form the \(\mathrm{Sb}-\mathrm{H}\) bonds: pure \(p\) orbitals or hybrid orbitals? Explain your reasoning.

Describe the changes in molecular geometry and hybridization that take place during the following reactions: (a) \(\mathrm{BF}_{3}+\mathrm{F}^{-} \longrightarrow \mathrm{BF}_{4}^{-}\) (b) \(\mathrm{PCl}_{5}+\mathrm{Cl}^{-} \longrightarrow \mathrm{PCl}_{4}^{-}\) (c) \(\mathrm{ICl}_{3}+\mathrm{Cl}^{-} \longrightarrow \mathrm{ICl}_{4}^{-}\) (d) \(\mathrm{PCl}_{3}+\mathrm{Cl}_{2} \longrightarrow \mathrm{PCl}_{5}\) (e) \(\mathrm{C}_{2} \mathrm{H}_{2}+\mathrm{H}_{2} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}\)

Which one of the following five diagrams best represents the structure of \(\mathrm{BrCl}_{4}^{+} ?\) a. b. c. d. e.

Cyclopropane is a triangular molecule with \(\mathrm{C}-\mathrm{C}-\mathrm{C}\) bond angles of \(60^{\circ} .\) Explain why the \(\sigma\) bonds joining carbon atoms in cyclopropane are weaker than the carboncarbon \(\sigma\) bonds in the noncyclic propane.

\(A\) lone pair of electrons in the valence shell of an atom has a larger effective volume than a bonding electron pair. Lone pairs therefore repel other electron pairs more strongly than do bonding pairs. On the basis of these statements, describe how the bond angles in \(\mathrm{TeF}_{4}\) and \(\mathrm{BrF}_{5}\) deviate from those found in a trigonal bipyramid and an octahedron, respectively. Sketch the molecular shapes of \(\mathrm{TeF}_{4}\) and \(\mathrm{BrF}_{5}\) and indicate these deviations on your drawing.

An ammonia molecule, \(\mathrm{NH}_{3}\), is very polar, whereas \(\mathrm{NF}_{3}\) is almost nonpolar. Use this observation along with the valence bond description of bonding in these molecules to justify the following statement: Lone pairs in bybrid or- bitals contribute to the overall dipole moment of a molecule.

Compare and contrast the concepts of delocalization and resonance.

Molecular orbital theory predicts the existence of antibonding molecular orbitals. How do antibonding electrons affect the stability in a molecule?