Chapter 9

Explain why \(\mathrm{He}_{2}\) does not exist but \(\mathrm{H}_{2}\) does.

How does MO theory account for the paramagnetism of \(\mathrm{O}_{2} ?\)

What relationship is there between bond order and bond energy?

What is the theoretical basis of both valence bond \((\mathrm{VB})\) theory and molecular orbital (MO) theory?

What shortcomings of Lewis structures and VSEPR theory do \(\mathrm{VB}\) and \(\mathrm{MO}\) theories attempt to overcome?

What is the main difference in the way VB and MO theories view the bonds in a molecule?

What effect does delocalization have on the stability of the electronic structure of a molecule?

What is a conduction band? What is a valence band?

On the basis of the band theory of solids, how do conductors, insulators, and semiconductors differ?

Why does electrical conductivity in semiconductors increase with increasing temperature?