X - X bond F - F Cl - Cl Br-Br I-I Bond dissociation 38 57 45.5 35.6 energy(kcl/mol) The lower value of bond dissociation energy of fluorine is due to the high inter-electronic repulsions between non-bonding electrons in the 2p-orbitals of fluorine. As a result F - F bond is weaker in comparison to Cl Cl and Br - Br bonds.