[Ashutosh]

what is the defination of bond order
 I know two formulae for calculating bond order.
1. bond order=1/2(bonding electrons-antibonding electrons)
                         AND
2. bond order=number of bonds in the molecule/number of resonating structures
    Are these two bond ordere same
    Do we get same bond order by using these formulae for the same molecule ???please explain with suitable example.
    what is the use of calculating bond order
    I know if bond order zero or negative then the molecule is unstable.But I think antibonding electrons cant exced bonding electrons.If yes give me a suitable example and explain.
    If yes,explain the unstability of CH(OH)3 on this basis.
    thanks for helping.

[Donaldson Tan]

the first definition is with regards to MO theory while the 2nd definition holds its regards to the valence bond theory. both are valid with respect to their originating theory.

a more modern definition of bond order will follow the MO theory definition because it encompasses quantum theory and it actually agrees with experimental results.

[pck24]

Although the MO approach does oversimplify the energy levels of the bonding and antibonding orbitals, in assuming that the energy penalty on filling an antibonding orbital exactly counters the energy reduction in filling the bonding.  If we use the simple "(number of electrons in bonding-number in antibonding)/2" we do not account for this.