AbstractExpressions for the extra ionic resonance energies Δ and Δ', the dissociation energy DAB and the force constant kAB of atomic bonds AB are deduced, containing only “free atom” electronegativities. Results obtained with these expressions are compared with experimental values, showing that Δ, Δ', DAB and kAB can be calculated starting from the expression of the polarity parameter λ from the MO equation ΦAB = N(ΦA + λΦB) as a function of the electronegativities ΦA and ΦB.