ABSTRACT
The problem of finding the electron orbits in a molecule is much more complicated than in atoms because the effective potential the electrons feel is no longer approximately spherically symmetric. One can picture the nuclei in a molecule as having classical equilibrium positions – points of minimum potential energy – about which they oscillate slowly, while the electrons travel rapidly around in the Coulomb potential of the nuclei. This simple picture of a molecule works because the nuclei are so much heavier than the electrons. The chemical activity of an atom depends on its having unpaired outer electrons, since only these lead to attractive interactions. Electrons in closed shells play little role in the binding of two atoms, since these electrons are closer to the nucleus than the valence electrons; at the actual separations of atoms in a molecule there is little overlap between electrons from one atom and the closed shell electrons from another.
