The molecular orbital σ formed by the addition of atomic orbitals is called the bonding molecular orbital while the molecular orbital σ* formed by the subtraction of atomic orbital is called antibonding molecular orbital.
The electron density in a bonding molecular orbital is located between the nuclei of the bonded atoms because of which the repulsion between the nuclei is very less while in case of an antibonding molecular orbital, most of the electron density is located away from the space between the nuclei. Infact, there is a nodal plane (on which the electron density is zero) between the nuclei and hence the repulsion between the nuclei is high.
| List-I | List-II | ||
| A | ΨMO=ΨA−ΨB | I | ABMO |
| B | μ=Q×r | II | Dipole moment |
| C | 2Nb−Na | III | Bond order |
| D | ΨMO=ΨA+ΨB | IV | BMO |