Chapter 9 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals - Study Questions - Page 369a: 20

See the answer below.

$Li_2^+$ has one valence electron and $Li_2^-$ has three, so the configuration is respectively: $[core]\ (\sigma_{2s})^1$ $[core]\ (\sigma_{2s})^2\ (\sigma_{2s}^*)^1$ Since $B.O.=(N.\ Bonding -N.\ Antibonding)/2$ These ions have a bond order of 0.5 thus having a weaker bond than $Li_2$ with a bond order of 1.