Group 13 Elements

Boron and fluorine do not have -orbitals. Hence, both of these participate in strong back -bonding. On the other hand, due to large size and availability of vacant -orbitals, Cl does not participate in such type of back -bonding. Hence, is less acidic than .

show back-bonding via formation of -bond due to :

(i) presence of vacant orbital in boron element and lone pair of electrons available in orbital of fluorine element.

(ii) Due to small size of boron and fluorine atoms, -bond (a back bond) is formed in addition to \sigma-bond between and atoms.