Figure 4.2. Two examples of axis distortions under volume conservation. Ellipses represent Jahn-Teller type distortions that occur when one p-orbital is occupied. The wave functions that result are hybrids of s and p orbitals. Elongation along the x-axis is limited by increased energy of the occupied s-like orbital. An analogous phenomenon occurs if the volume is a box containing electrons. Shown are the quantum numbers of the highest occupied orbitals nx,ny,nz and the approximate distortions that occur to minimize the total energy. The first is 'closed shell' with 16 electrons and the second with 17 or 18 electrons would, if it existed, have a low IP.