# Are polar bond stronger than non-polar bonds?

I came across Pauling's electronegativity scale in which he noticed that the experimental bond enthalpy of X-Y is always greater than the average of X-X & Y-Y and proposed that the difference, D, between the experimental bond enthalpy and the average of X-X & Y-Y gave a measure of the ionic character/polarity of the bond/ electronegativity difference

This seems to imply that the greater the electronegativity difference, the higher the bond dissociation enthalpy (as compared to the average of X-X & Y-Y).

I can't think of any explanation for this though. I came across one explanation stating that the partial charges result in an extra electrostatic attraction, but I can't find any reliable source for verification

• chemistry.stackexchange.com/questions/129328/… Feb 4 at 15:28
• This also indicates that ionic bonds are equally or more strong that a number of covalents one. Although the opposite is often claimed by books and teachers. Feb 5 at 10:40

Pauling's original definition of electronegativity relied on the idea that the bond dissociation energy contains contributions from a QM interaction plus an additional purely electrostatic interaction (a classical Coulombic interaction not involving a QM description of chemical bonds). In homonuclear diatomic molecules the electrostatic term is not important because the atoms "tug" at the electrons with equal strength, and so only a QM term contributes to bonding. For heteronuclear diatomics one can estimate the magnitude of the contribution of the QM term as an average of the terms in the two homonuclear molecules. Subtracting this average from the dissociation energy for the heteronuclear diatomic then results in an estimate of an electrostatic contribution to bonding. The electrostatic contribution is argued to be due to the different electron attraction in the two atoms, which is encoded in Pauling's electronegativity parameter. This is summarized by the equation for the heat of formation postulated by Pauling (in $$\pu{kJ/mol}$$): $$Q_f = 100 (\chi_A-\chi_B)^2$$