Class 11 NEET Chemistry Classification Of Elements And Periodicity In Properties

Due to more repulsion in between non-bonding electron pair (2p) of two fluorines (due to small size of F-atom) in comparison to non-bonding electron pair (3p) in chlorine, the bond energy of F2 is less than Cl2.
B.E.(F2)=158.5‌kJ‌/‌mole‌ and ‌
B.E.(Cl2)=242.6‌kJ‌/‌mole