CHEM 121 glossary

Bonding molecular orbital

A molecular orbital from the in-phase combination of atomic orbitals, with electron density built up between the nuclei. It lies lower in energy than the atomic orbitals it came from, so electrons in it hold the atoms together and raise the bond order.

\ce{H}

atom

\ce{H2^{+}}

MOs

\ce{H}

atom

$\ce{H2+}$ : one electron in $\sigma_{1s}$ , below the two H $1s$ levels.

Example

$\ce{H2+}$ has a single electron, in $\sigma_{1s}$ : bond order ½, yet the ion is bound. In $\ce{N2}$ the bonding MOs $\sigma_{2s}$ , $\pi_{2p}$ (two) and $\sigma_{2p}$ hold 8 of the 10 valence electrons.