Chemistry

An Overview about the Chemical Element Mercury



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Mercury

Symbol: Hg

Atomic Number: 80

Atomic Mass: 200.59 amu (atomic mass units)

Melting Point: minus 38.83 °C (234.32 K, minus 37.89 °F)

Boiling Point: 356.73 °C (629.88 K, 674.11 °F)

Number of Protons: 80

Number of Electrons: 80

Number of Neutrons: 121

Classification: Transition Metal

Crystal Structure: Rhombohedral

Density @ 293 K: 13.456 grams per cubic centimeter

Color: Silver

This element has been known since ancient times. Tubes of it have been found in tombs of ancient Egypt dated to 1500 BCE, while the ancient Chinese appear to have known of it at least 4000 years ago. It is named after the Roman messenger god and the planet closest to the sun. The symbol Hg is derived from the Greek word “hydrargyrum”, which means liquid silver.

Mercury is one of only two elements that are liquid at room temperature the other being bromine. It is the only metal that is liquid at room temperature. It is rarely found free in nature but is found in the ore cinnabar. Compared to other metals is conducts heat poorly and is a fair conductor of electricity. It forms alloys with many metals including gold and silver. Alloys of mercury are call amalgams. The triple point of mercury, minus 38.8344 °C (234.3156 K, minus 37.90192 °F), is one of the fixed points on the International Temperature Scale.

It is toxic and the recommended safety limit of 0.1 milligrams per cubic meter of air can be reached easily if the element is handled in a poorly ventilated area. Mercury should, therefore, be handled in a properly vented safety hood.

Extraction from the ore cinnabar involves heating the ore in a current of air to above 600 °C (873 K, 1112 °F). This causes the mercury to vaporize it can then be condensed into crude liquid mercury. The crude mercury is treated with nitric acid to remove such impurities as oxides. If further purification is required the mercury can be distilled at a reduced pressure.

Mercury has found many uses over the centuries. The ancient Greeks used it for medicinal purposes while the Romans used it to make cosmetics. The alchemists used it in their experiments and knew it as quicksilver.

Today mercury and its compounds still have many uses.

* It is used in thermometers and barometers.

* Other laboratory equipment including diffusion pumps make use of mercury.

* Mercury is used in some electrical devices such as mercury switches.

* It is used as an electrode in some forms of electrolysis.

* In lighting it is used for mercury vapor lamps and illuminated advertising signs.

* Mercury cells are used in the production of chlorine and caustic soda.

* Used in the preparation of dental amalgams.

* Mercurous chloride or calomel is sometimes used in medicine. This should not be confused with mercuric chloride, which is a corrosive sublimate and a virulent poison.

* Mercury fulminate is used in blasting caps.

* Mercuric sulfide is the high-grade paint pigment known as vermillion.

* It has found a use as a basis for antifouling paints and pesticides.

The ability of mercury to form an amalgam with gold has led to it being used to extract gold from its ores. Unfortunately, much of this extraction is unregulated and, in some parts of the world, mercury pollution from gold mining areas is threatening the whole ecosystem of river systems.

Reference sources:

Los Alamos National Laboratory Chemistry Division

Jefferson Laboratories Science Education website

Web Elements


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