Bond Order
The number of chemical bonds between a pair of atoms, or in molecular orbital terms half the difference between bonding and antibonding electrons.
Formula / equation
BO = (N_b − N_a) / 2
Unit
Dimensionless
In depth
Higher bond order means a shorter, stronger bond. Molecular orbital theory allows fractional values, which is how it explains species like O₂⁺ and the one-electron bond in H₂⁺. A bond order of zero predicts that the species cannot exist, correctly ruling out Ne₂ and He₂.
Examples in the real world
N₂ has bond order 3 and a very short 110 pm bond; O₂ has 2; benzene's C–C bonds average 1.5.