Chapter 9

What are molecular orbitals? How do they compare with atomic orbitals? Can you tell by the shape of the bonding and antibonding orbitals which is lower in energy? Explain.

Explain the difference between the $\sigma$ and $\pi$ MOs for homo- nuclear diatomic molecules. How are bonding and antibonding orbitals different? Why are there two $\pi$ MOs and one $\sigma$ MO? Why are the $\pi$ MOs degenerate?

Draw the Lewis structure for HCN. Indicate the hybrid orbitals, and draw a picture showing all the bonds between the atoms, labeling each bond as $\sigma$ or $\pi .$

Which is the more correct statement: "The methane molecule $\left({\mathrm{CH}}_4\right)$ is a tetrahedral molecule because it is $s{p}^3$ hybridized" or "The methane molecule (CH_ ${}_4)$ is $s{p}^3$ hybridized because it is a tetrahedral molecule"? What, if anything, is the difference between these two statements?

What are the relationships among bond order, bond energy, and bond length? Which of these quantities can be measured?

The molecules ${\mathrm{N}}_2$ and $\mathrm{CO}$ are isoelectronic but their properties are quite different. Although as a first approximation we often use the same MO diagram for both, suggest how the $\mathrm{MOs}$ in ${\mathrm{N}}_2$ and $\mathrm{CO}$ might be different.

Do lone pairs about a central atom affect the hybridization of the central atom? If so, how?

In the hybrid orbital model, compare and contrast $\sigma$ bonds with $\pi$ bonds. What orbitals form the $\sigma$ bonds and what orbitals form the $\pi$ bonds? Assume the $z$ -axis is the internuclear axis.

In the molecular orbital model, compare and contrast $\sigma$ bonds with $\pi$ bonds. What orbitals form the $\sigma$ bonds and what orbitals form the $\pi$ bonds? Assume the $z$ -axis is the internuclear axis.

Why are $d$ orbitals sometimes used to form hybrid orbitals? Which period of elements does not use $d$ orbitals for hybridization? If necessary, which $d$ orbitals $(3d,4d,5d,\text{ or }6d)$ would sulfur use to form hybrid orbitals requiring $d$ atomic orbitals? Answer the same question for arsenic and for iodine.