  Chemical bonds are considered in light of correlation of valence electrons
that is strengthened when the bond is dissociated. In the framework of the
unrestricted Hartree-Fock single-reference version of the configuration
interaction theory, effectively unpaired electrons lay the foundation of the
electron correlation measure in terms of total number of the electrons
(molecular chemical susceptibility). graphs and their singularities with
respect to the interatomic distance allow presenting a quantitative description
of stretching and breaking of chemical bonds. The approach validity is
demonstrated on a large number of bonds of different order and chemical
composition.
