Bond dissociation enthalpy of F-F bond is less than that of Cl-Cl bond. Explain.

Explanation

Bond length of F-F bond (143 pm) is less than that of Cl-Cl bond (199 pm). Therefore, bond dissociation enthalpy or bond energy of `F_(2)` is expected to be more than that of `Cl_(2)`. But actually it is less. This is on account of greater force of repulsion in the non-bonded (lone) electron pairs in the molecule of `F_(2)overset(* *)underset(* *)( :F: )overset(* *)underset(* *)(F: )` than in `Cl_(2)` as a result of which the bond cleavage is easier.