“The amount of energy required to break one mole of bonds of a particular type so as to separate them into gaseous atoms is called bond dissociation energy or simply bond energy”. Greater is the bond energy, stronger is the bond. Bond energy is usually expressed in kJmol-1.
Factors affecting bond energy
(i) Greater the size of the atom, greater is the bond length and less is the bond dissociation energy i.e. less is the bond strength.
(ii) For the bond between the two similar atoms, greater is the multiplicity of the bond, greater is the bond dissociation energy.
(iii) Greater the number of lone pairs of electrons present on the bonded atoms, greater is the repulsion between the atoms and hence less is the bond dissociation energy.
(iv) The bond energy increases as the hybrid orbitals have greater amount of s orbital contribution. Thus, bond energy decreases in the following order, sp>sp2>sp3
(v) Greater the electronegativity difference, greater is the bond polarity and hence greater will be the bond strength i.e., bond energy, H-F>H-Cl>HBr>H-I,
(vi) Among halogens Cl – Cl > F – F > Br – Br > I – I, (Decreasing order of bond energy) Resonance increases bond energy.