where D denominator is a function of kinetic exchange interaction J kex and effective Coulomb interaction E ef f . In the ionic regime, (t + V ) contribution should be smaller than (U -K), whereas in the covalent regime, it is predominant. But, as one can expect, the ionic regime is unphysical as we consider the two-atomic homonuclear molecule. In the opposite case, (t + V ) contribution is of larger magnitude than (U -K). Although, in general, the mechanism of covalent bond formation is consistent with that proposed by Reudenberg, there are fundamental differences between his and our solution. In Reudenberg's analysis, kinetic energy is the energy associated with the motion of electrons, whereas the exchange interaction energy is related to the virtually resonating electrons in agreement with the understanding of covalent processes. The potential energy in Ruendenberg's analysis is calculated based on the electrostatic interactions between charged particles (nuclei and electrons) whereas in our case it is the difference between intraatomic and interatomic Coulomb repulsion, which is more natural to the discussion of ionic bonding.