Mercury

Atomic Number:

80

Melting Point: -38.83 C
Atomic Symbol: Hg Boiling Point:  356.73 C
Atomic Weight: 200.59 amu Density: 13579.04 kg/m 3
Atomic Radius:

160 pm

Oxidation States: 2, 1
Covalent Radius: 149 pm Electron Configuration: [Xe]6s24f145d10
van der Waals Radius:

155 pm

State of Matter:  liquid

History

(Gk. hydoor, living and argyros, silver) Known to ancient Chinese and Hindus; found in Egyptian tombs of 1500 B.C. It was named by alchemists after the Roman god Mercury. Its symbol, Hg, comes from the Latin word, hydrargyrum, borrowed from the Greek word hydrargyros, which was a compound word whose Greek roots meant 'water' and 'silver'.

Properties

Mercury is the only common metal liquid at ordinary temperatures. It is a heavy, silvery-white metal; a rather poor conductor of heat, as compared with other metals, and a fair conductor of electricity. It easily forms alloys with many metals, such as gold, silver, and tin, which are called amalgams. Its ease in amalgamating with gold is made use of in the recovery of gold from its ores. Mercury is a virulent poison and is readily absorbed through the respiratory tract, the gastrointestinal tract, or through unbroken skin. It acts as a cumulative poison and dangerous levels are readily attained in air. Air saturated with mercury vapor at 20C contains a concentration that exceeds the toxicity limits. The danger increases at higher temperatures. It is  important therefore that mercury be handled with care.  Methyl mercury is a dangerous pollutant and is now widely found in water and streams. The triple point of mercury, -38.8344C, is a fixed point on the International Temperature Scale (ITS-90).

Sources & Compounds

A rare element in the earth's crust, mercury is found either as a native metal (rare) or in cinnabar, corderoite, livingstonite, and other minerals with cinnabar being the most common ore. Approximately 50% of the global supply comes from Spain and Italy, with much of the rest coming from Slovenia, Russia, and North America. The metal is extracted by heating cinnabar in a current of air and condensing the vapor.

The most important salts are mercury chloride (corrosive sublimate - a violent poison), mercurous chloride (calomel, occasionally still used in medicine), mercury fulminate, a detonator widely used in explosives, and mercuric sulfide (vermilion, a high-grade paint pigment).

Organic mercury compounds are also important. Laboratory test have found that electrical discharge causes the noble gases to combine with mercury vapor. These compounds are held together with van der Waals forces and result in HgNe, HgAr, HgKr, and HgXe. Methyl mercury  is a dangerous compound that is widely found as a pollutant in water bodies and streams.

Uses

The metal is widely used in laboratory work for making thermometers, barometers, diffusion pumps, and many other instruments. It is used in making mercury-vapor lamps and advertising signs, etc. and is used in mercury switches and other electronic apparatus. Other uses are in making pesticides, Mercury cells for caustic soda and chlorine production, dental preparations, anti-fouling paint, batteries, and catalysts.

Isotopes

There are seven stable isotopes of mercury with Hg-202 being the most abundant (26.86%). The longest-lived radioisotopes are Hg-194 with a half-life of 444 years, and Hg-203 with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lifes that are less than a day.

Hazards

Elemental, liquid mercury is slightly toxic, while its vapor, compounds and salts are highly toxic and have been implicated as causing brain and liver damage when ingested, inhaled or contacted. For this reason, most thermometers now use pigmented alcohol instead of mercury, though some medical thermometers still use mercury for reasons of accuracy.

The main dangers associated with elemental mercury are that at STP, mercury tends to oxidize forming mercury (II) oxide, and that if dropped or disturbed, mercury will form microscopic drops, increasing its surface area dramatically.

Even though it is far less toxic than its compounds, elemental mercury still poses significant environmental pollution and remediation problems due to the fact that mercury forms organic compounds inside of living organisms. Methyl mercury works its way up the food chain, reaching high concentrations among populations of some species such as tuna. Mercury poisoning in humans will result from persistent consumption of tainted foodstuffs.

One of the most dangerous mercury compounds, dimethylmercury, is so toxic that even a few microliters spilled on the skin can cause death.

Mercury is a bioaccumulative toxin that is easily absorbed through the skin, respiratory and gastrointestinal tissues. Minamata disease is a form of mercury poisoning. Mercury attacks the central nervous system and adversely affects the mouth, gums, and teeth. High exposure over long periods of time will result in brain damage and ultimately death. It can pose a major health risk to the unborn fetus. Air saturated with mercury vapor at room temperature is at a concentration many times the toxic level, despite the high boiling point (the danger is increased at higher temperatures).

Mercury should therefore be handled with great care. Containers of mercury need to be covered securely to avoid spillage and evaporation. Heating of mercury or mercury compounds should always be done under a well-ventilated, filtered hood. Additionally, some oxides can decompose into elemental mercury, which immediately evaporates and may not be apparent.