Relativistic Effects

Schrödinger's equation does not take into account influences that are significant when particles travel at a speed comparable with that of light. There are two significant features: moving charged particles experience magnetic with electric fields; and also the special theory of relativity predicts influence such an improvement of the mass of fast-moving particles. These influences were incorporated into the quantum mechanical wave theory by Dirac's equation (1928).

One significant prediction is the presence of electron spin and the occurrence of spin-orbit splitting in atomic spectra. The energies of orbitals are also changed, particularly for electrons close to highly charged nuclei, because it is then that they are travelling fast. Inner shells are most influenced but they are not significant in chemistry. For very heavy elements even the outer shells depict an affect of relativity. This is right for the 6s shell in mercury and gold and the 6p shell in consequent elements of period 6. Relativistic affects increments the binding energy of these electrons. So, they contribute to the irregularities in group trends, and make a considerable contribution to the high IEs and therefore chemical inertness of some heavy elements particularly gold and mercury.