- Relativistic quantum chemistry
**Relativistic quantum chemistry**is a branch ofquantum chemistry that applies relativistic mechanics, and, in particular theDirac equation or an approximation to it (e.g., at the lowest level, thePauli equation ), toelectron dynamics andchemical bonding , especially the behavior of the heavier elements of theperiodic table .Many of the chemical and physical differences between the 6th Row (Cs-Rn) and the 5th Row (Rb-Xe) arise from the larger

**relativistic effects**for the former. These relativistic effects are particularly large for gold and its neighbours, platinum and mercury.Some of the phenomena commonly attributed to relativistic effects are:

* The low melting point of mercury

* The stability of the Hg_{2}^{2+}ion

* The stability ofMercury(IV) fluoride

*Aurophilicity

* The stability of the gold anion, Au^{−}, in compounds such as CsAu

* The color ofgold

* The preference for higher oxidation states among metals in the third transition series, W-Au

* Theinert pair effect inthalium ,lead , andbismuth , which leads to lower oxidation states

* The crystal structure of lead, which isface-centered cubic instead of diamond-like

* The striking similarity betweenzirconium andhafnium

* The stability of theuranyl cation , as well as other high oxidation states in the earlyactinide s (Pa-Am)

* The small atomic radii offrancium andradium

* About 10% of thelanthanide contraction is attributed to relativistic effects**References*** P. A. Christiansen; W. C. Ermler; K. S. Pitzer. Relativistic Effects in Chemical Systems. "Annual view of Physical Chemistry"

**1985**, "36", 407-432. doi|10.1146/annurev.pc.36.100185.002203

* Pekka Pyykko. Relativistic effects in structural chemistry. "Chem. Rev."**1988**, "88", 563-594.

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