mercury (element)

mercury (element)
Name	mercury
Number	80
Category	transition metal
Group	12
Appearance	silvery, liquid
Standard atomic weight	200.592
Electron configuration	[Xe] 4f14 5d10 6s2
Phase	liquid
Melting point degC	-38.83
Boiling point degC	356.73
Density g cm3	13.534
Atomic radius empirical	151 pm
Crystal structure	rhombohedral
Oxidation states	−2, +1, +2
Electronegativity	2.00
Ionization energies	1007.1, 1810, 3300 kJ/mol

mercury (element). Mercury is a chemical element with the symbol Hg and atomic number 80. It is a heavy, silvery d-block metal, notable for being liquid at standard conditions for temperature and pressure. Known since antiquity, it is often referred to as quicksilver and was named for the Roman god Mercury (mythology). Its unique physical properties and high toxicity have made it a subject of significant scientific and industrial interest.

Characteristics

Mercury is the only metallic element that is liquid at room temperature, a property it shares with the halogen bromine. It has a very high surface tension, forming rounded beads when spilled, and a relatively high electrical conductivity. The element exhibits a low melting point of -38.83 °C and a boiling point of 356.73 °C. Its liquid range is the narrowest of any metal. Mercury readily forms alloys, known as amalgams, with many metals including gold, silver, and tin, but not with iron. This property was historically exploited in mining processes like those used in the California Gold Rush. The element's high density is exemplified by the fact that lead floats on its surface.

Occurrence and production

Mercury is a relatively rare element in Earth's crust, occurring primarily in the form of the red sulfide ore cinnabar. Major deposits are found in regions such as Almadén in Spain, which has been a significant source for centuries, Idrija in Slovenia, and Huancavelica in Peru. It is also found in smaller quantities in China, Kyrgyzstan, and Mexico. The primary method of extraction involves roasting cinnabar in air, producing mercury vapor which is then condensed. This process can release significant amounts of the element into the environment. Global production has declined due to environmental and health concerns, with major operations like the McDermitt Mine in the United States having ceased.

Chemical properties and compounds

Mercury exists in oxidation states +1 (mercurous) and +2 (mercuric), with the +2 state being more stable and common. Notable compounds include the corrosive and toxic mercury(II) chloride (corrosive sublimate), the explosive mercury(II) fulminate used in detonators, and the pigment vermilion derived from mercury sulfide. Mercurous compounds often contain the dimeric cation Hg₂²⁺, as in calomel (mercury(I) chloride), historically used in medicine. The element does not react with most acids but dissolves in nitric acid. Organomercury compounds, such as methylmercury, are highly toxic and form through environmental processes.

Applications

Historically, mercury was used extensively in scientific instruments like barometers, thermometers, and manometers, inventions often credited to figures like Evangelista Torricelli and Daniel Gabriel Fahrenheit. Its use in electrical equipment, including fluorescent lamps, tilt switches, and some battery types like mercury batteries, was once widespread. The chloralkali process employed mercury cells for the production of chlorine and sodium hydroxide. Its use in dentistry for dental amalgam fillings has declined but persists. Modern applications are more niche, including use in some semiconductors and as a catalyst in the chemical industry.

Biological role and toxicity

Mercury has no known biological role and is a potent neurotoxin. Exposure, primarily to methylmercury through contaminated fish consumption, or to elemental mercury vapor, can cause severe damage to the nervous system, kidneys, and other organs. Historical incidents of mass poisoning include Minamata disease in Japan caused by industrial discharge from the Chisso Corporation, and acrodynia (pink disease) in children. The compound thiomersal is a preservative in some vaccines. Due to its high toxicity, its use is heavily regulated by bodies like the United States Environmental Protection Agency and international agreements such as the Minamata Convention on Mercury.

History

Mercury has been known for millennia, with evidence of its use found in Ancient Egyptian tombs dating to 1500 BCE. The ancient Greeks and Romans used it in ointments and for refining precious metals. The alchemists of the Islamic Golden Age, including Jabir ibn Hayyan, and later European alchemists like Paracelsus, considered it a fundamental principle. Its use in gilding and silvering was common. Major scientific study advanced in the 18th and 19th centuries with the work of Antoine Lavoisier and Humphry Davy. The 20th century saw a growing understanding of its environmental and health impacts, leading to widespread restrictions.

Category:Chemical elements Category:Transition metals Category:Neurotoxins