Question

What is the significance of the term half filled atomic orbitals in the valance bond theory

Answer 1

Half filled orbitals are those with each of their spatial orientation half filled. Due to symmetry the orbitals are thus at a semi low level energy state as all spatial positions have maximum distance between them. When numbet of electron is low or high the symmetry of repulsion between electrons is lost and thus leads to a more unstable state. When fully filled the effect of positive spin electron is overcome by the negative spin electron in the same orbital and this configuration is more stable than half filled one.