In the given expression the wave function is expressed as a linear combination of two terms: ψ cov (r 1 , r 2 ) and ψ ion (r 1 , r 2 ). Covalent C and ionic I factors are functions of microscopic parameters introduced in the previous subsection. We consider the physical picture of why the chemical homopolar bond is covalent when the kinetic exchange interaction is higher than the effective Coulomb interaction. To do that we examine coefficients of the wave function from Eq. ( ), where all parameters were explained but the role of D can still be difficult to grasp. The expression D = 16(t + V ) 2 + (U -K) determines the energy denominator of the wave function. Because our goal is to study the bonding factor as the ratio of kinetic energy to potential energy one can write it in the form