As illustrated in figure 1, Hund was primarily concerned with characterizing the electronic energy eigenfunctions in terms of the quantum numbers for the limiting cases of united and widely separated atoms, as the distance between the atoms is changed adiabatically from zero to infinity. He explained the sharing of an electron between the atoms represented by the potential wells—so fundamental for an understanding of covalent chemical binding—and discussed the distinction between classical orbits and quantum mechanical wavefunctions.
