Relativistic quantum chemistry

The relativistic effect describes the physical chemistry properties of heavy atoms, which can only be explained by the use of relativistic quantum mechanics. Prime example of this is the striking difference in color of silver and gold. But the liquid state of mercury can be explained by the relativistic effect. The effect affects mainly for heavy atoms. One consequence of the relativistic effect is that the assignment of artificial chemical elements ( high atomic number ) to the groups of the periodic table is uncertain. For example, it was discussed whether Copernicium noble gas properties.

The relativistic effect also explains the " effect of the inert electron pair " (inert pair effect), because the outermost pair of electrons in the valence s- orbital is apparently inert.

Theoretical considerations

For the heavy elements from the 6th period of the periodic table, the electrons in the vicinity of the nucleus speeds, only just below the speed of light. This requires, takes its mass ( relativistic mass increase ). The increased mass in turn resulting in a contraction of the s- orbitals (and some p- orbitals ). As a result, the electron shield the nuclear charge better and the energy levels of the orbitals of the other are lifted.

Mathematics is necessary to replace the nonrelativistic Hamiltonian against a relativist. This is successful with atoms relatively well with the Dirac equation instead of the Schrödinger equation. For the lighter elements predominate terms as the wide correction for the electron -electron interaction and quantum electrodynamics ( QED ) of the vacuum polarization and vacuum fluctuation. Approximately from the atomic number 50 the latter term does not matter, because the vacuum polarization and the vacuum fluctuation assume almost the same values. Within a group of the periodic table takes the term for relativistic effects to Z2 and reached in 6th period, a not -negligible size. Therefore, they must ( atomic number 55 ) are respected for elements from cesium.

Wherein the elements of the fifth period of the Periodic Table of the lanthanide plays a crucial role in order to describe the behavior. After this, however, would have the s- and d- energy levels from silver and gold to be about the same. However, is observed when gold is a contraction of the 6s and an expansion of the 5d levels. When Copernicium ( atomic number 112 ), this effect is even more pronounced; Possibly the difference in level between the 6d and the 8p electrons is so large that Copernicium noble gas character possesses.

Examples

In the nonrelativistic case, the 5d and 6s energy levels of silver and gold would be similar. Due to the relativistic effect, the 6s levels are, however, contracted and the 5d levels expanded. The result is an energy difference corresponding to the wavelength of blue light (blue light is absorbed, remains the well-known golden yellow color). Simultaneously, the bond lengths are shortened in gold compounds ( about 20 pm in the gold dimer). When element Roentgenium this effect is probably even more pronounced.

The tendency of heavy elements to form oxides, does not follow the expected properties. PbO as the stable oxygen compound of the lead, whereas silicon, germanium and tin form stable form of MeO2 Dioxide. According to theoretical estimates is also a large part of the electrical voltage which is applied to the poles of the lead-acid battery, caused by the relativity. It is also not a stable bismuth ( V) oxide is known, of phosphorus, arsenic and antimony, but already.