To determine the bond order, you subtract the antibonding electrons from the bonding electrons and divide by 2.
The formula for bond order is
Bond Order = ½(b - a)
where b is the number of bonding electrons and a is the number of antibonding electrons.
You first draw the molecular orbital diagram for the molecule. Let’s use C₂ as an example.
You put the eight valence electrons in the lowest orbitals:
You have six bonding and two antibonding electrons. The bond order is
Bond Order = ½(b - a), = ½(6 – 2) = ½ × 4 = 2
Calculate the bond order in C₂²⁺.
Here we have only six valence electrons. They are in the
Bond Order=½(b - a), = ½(4 – 2) = ½ × 2 = 1