41In the Molecular Orbital (MO) approach to chemical bonding, a bond is considered to be formed when two atomic orbitals (AOs) combine to give two molecular orbitals. One of these MOs is of lower energy than the AOs this is the "bonding" MO and one is higher energy than the AOs and this is the "anti bonding" MO. Where each of the AOs is singly occupied only the bonding MO will be filled. In bonding MOs the electron density is concentrated between the nuclii and in antibonding MOs it is concentrated outside this volume.
