Bonding and anti-bonding orbitals

Bonding and anti-bonding orbitals

When two atomic orbitals overlap, the nature of the molecular orbital (M.O.) depends on whether the overlap occurs between two regions having the same sign or opposite signs. When the former occurs, the result is a bonding orbital, whereas when the latter occurs, the result is an anti-bonding orbital. In some cases, two orbitals of opposite sing cancel out each other; the result is non-bonding. In bonding orbitals, the electron charge is concentrated in the region between the two nuclei, thereby holding the two nuclei together. On the other hand, in anti-bonding orbitals electron charge is withdrawn from the region between the two nuclei, thereby resulting in increased repulsion between the two nuclei.

The normal symbols,  and  , used to designate bonding orbitals, are started to designate the corresponding anti-bonding orbitals. Above picture illustrate combination of various A.O.s , the anti-bonding orbital involving the reversal of the sign (or signs) in one of the orbitals (arbitrarily the one of the right-hand side). In general, if n A.O. s are combined, then there are n M.O.s. Some of these are bonding, other anti-bonding, and in fewer cases, some are non-bonding.