8.4 Molecular Orbital Theory

How are the following similar, and how do they differ?

(a) σ molecular orbitals and π molecular orbitals

(b) ψ for an atomic orbital and ψ for a molecular orbital

(c) bonding orbitals and antibonding orbitals

Can a molecule with an odd number of electrons ever be diamagnetic? Explain why or why not.

Why are bonding molecular orbitals lower in energy than the parent atomic orbitals?

Explain why an electron in the bonding molecular orbital in the H₂ molecule has a lower energy than an electron in the 1s atomic orbital of either of the separated hydrogen atoms.

Determine the bond order of each member of the following groups, and determine which member of each group is predicted by the molecular orbital model to have the strongest bond.

(a) H₂, $\text{H}_{2} ^{+} ,$ $\text{H}_{2} ^{−}$

(b) O₂, $\text{O}_{2} ^{\text{2}+} ,$ $\text{O}_{2} ^{\text{2}−}$

(c) Li₂, $\text{Be}_{2} ^{+} ,$ Be₂

(d) F₂, $\text{F}_{2} ^{+} ,$ $\text{F}_{2} ^{−}$

(e) N₂, $\text{N}_{2} ^{+} ,$ $\text{N}_{2} ^{−}$

Compare the atomic and molecular orbital diagrams to identify the member of each of the following pairs that has the highest first ionization energy (the most tightly bound electron) in the gas phase:

(a) H and H₂

(b) N and N₂

(c) O and O₂

(d) C and C₂

(e) B and B₂

A friend tells you that the 2s orbital for fluorine starts off at a much lower energy than the 2s orbital for lithium, so the resulting σ_2s molecular orbital in F₂ is more stable than in Li₂. Do you agree?

What charge would be needed on F₂ to generate an ion with a bond order of 2?

Explain why $\text{N}_{2} ^{\text{2}+}$ is diamagnetic, while $\text{O}_{2} ^{\text{4}+} ,$ which has the same number of valence electrons, is paramagnetic.