Mercury

---

MELTING POINT: −38.87°C
BOILING POINT: 359.6°C
DENSITY: 13.54 g/cm ³
MOST COMMON IONS: Hg ₂ ²⁻ , Hg ²⁺

Mercury is at room temperature a silver-white, volatile liquid metal . It is reputed to have been known in ancient Egypt. Dioscorides, a Greek physician who flourished ca. 60 C.E. , recounted the condensation of mercury vapor after the heating of cinnabar, the major ore of mercury. In the modern era mercury is produced via a variation on the procedure used by the ancients: The bright red ore (cinnabar) is now heated in oxygen, with lime, or with iron.

HgS(s) + O ₂ (g) → SO ₂ (g) + Hg

HgS(s) + Fe → Hg + FeS

4HgS(s) + 4CaO(s) → 4Hg + 3CaS(s) + CaSO ₄ (s)

Mercury has three oxidation states: 0, 1+ (mercurous), and 2+ (mercuric). It forms few simple compounds. It does form several simple, water-soluble mercuric compounds: mercuric chloride, HgCl ₂ ; mercuric nitrate, Hg(NO ₃ ) ₂ ; and mercuric acetate, Hg(CH ₃ COO) ₂ . The mercurous chloride, Hg ₂ Cl ₂ , is insoluble in water. Relatively stable organometallic compounds are formed with aliphatic and organic compounds. Methylmercury (CH ₃ –Hg ⁺ ) is the major polluting form of mercury. Methylmercury reacts with thiol groups in enzymes.

The mining of mercury has declined in recent decades, as major international concern over the health threat of mercury's extensive pollution of the environment has mounted. Much American freshwater fish is contaminated. The U.S. Environmental Protection Agency estimates 3,000 uses of mercury. Mercury usage is down in the chloroalkali industry, in which mercury is the cathode material used in the electrolysis of sodium chloride solutions, which produce sodium hydroxide and chlorine. An abundance of 500 ppb (0.5 μ g/g) in Earth's crust gives rise to a discharge into the atmosphere of mercury on combustion of fossil fuels and the manufacture of metals and cement.

SEE ALSO Heavy Metal Toxins ; Inorganic Chemistry .

Robert A. Bulman

Bibliography

Magos, L. (1987). "Mercury." In Handbook of the Toxicity of Inorganic Compounds, ed. Hans G. Seiler, Helmut Sigel, and Astrid Sigel. New York: Marcel Dekker.