magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.8°C;; b.p. about 1,090°C;; sp. gr. 1.738 at 20°C;; valence +2. In 1808, Sir Humphry Davy discovered magnesium in its oxide, although it is not certain that he isolated the metal. Pure magnesium was isolated substantially by A. A. B. Bussy in 1828 by chemical reduction of the chloride. Magnesium was first isolated electrolytically by Michael Faraday in 1833.

Properties

Magnesium is a ductile, silver-white, chemically active metal with a hexagonal close-packed crystalline structure. It is malleable when heated. Magnesium is one of the alkaline-earth metals alkaline-earth metals, metals constituting Group 2 of the periodic table . Generally, they are softer than most other metals, react readily with water (especially when heated), and are powerful reducing agents, but they are exceeded in each of these properties by the
..... Click the link for more information. in Group 2 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. . It reacts very slowly with cold water. It is not affected by dry air but tarnishes in moist air, forming a thin protective coating of basic magnesium carbonate, MgCO₃·Mg(OH)₂. When heated, magnesium powder or ribbon ignites and burns with an intense white light and releases large amounts of heat, forming the oxide, magnesia magnesia, common name for the chemical compound magnesium oxide, MgO. It occurs as colorless, cubic crystals. It is refractory, melting at about 2,800°C;. It is very slightly soluble in pure water but is soluble in acids and solutions of ammonium salts.
..... Click the link for more information. , MgO. A magnesium fire cannot be extinguished by water, since water reacts with hot magnesium and releases hydrogen. Magnesium reacts with the halogens and with almost all acids. It is a powerful reducing agent and is used to free other metals from their anhydrous halides.

Compounds

Magnesium forms many compounds. The oxide, hydroxide, chloride, carbonate, and sulfate are commercially important. They are used in ceramics, cosmetics, fertilizers, insulation, leather tanning, and textile processing. Epsom salts Epsom salts, common name for magnesium sulfate heptahydrate, MgSO₄·7H₂O, a water-soluble bitter-tasting compound that occurs as white or colorless needle-shaped crystals.
..... Click the link for more information. (magnesium sulfate heptahydrate, MgSO₄·7H₂O), milk of magnesia milk of magnesia, common name for the chemical compound magnesium hydroxide, Mg(OH)₂. The viscous, white, mildly alkaline mixture that is used medicinally as an antacid and laxative is a suspension of approximately 8% magnesium hydroxide in water.
..... Click the link for more information. (magnesium hydroxide, Mg(OH)₂), and citrate of magnesia are used in medicine. Magnesium reacts with organic halides to form the Grignard reagents Grignard reagent (grēnyärd` rēā`jənt)
..... Click the link for more information. of organic chemistry.

Natural Occurrence

Magnesium is the eighth most abundant element in the earth's crust but does not occur uncombined in nature. It is found in abundance in the minerals brucite, magnesite magnesite (măg`nəsīt), mineral, magnesium carbonate, MgCO₃, white, yellow, or gray in color.
..... Click the link for more information. , dolomite 1 Mineral, calcium magnesium carbonate, CaMg (CO₃)₂. It is commonly crystalline and is white, gray, brown, or reddish in color with a vitreous to pearly luster. The magnesium is sometimes replaced in part by iron or manganese.
..... Click the link for more information. , and carnalite. It is also found (as the silicate) in asbestos, meerschaum, serpentine, and talc. Magnesium chloride is found in seawater, brines, and salt wells. Mineral waters often contain salts of magnesium; the magnesium ion imparts a bitter flavor. Magnesium is a constituent of the chlorophyll in green plants and is necessary in the diet of animals and humans.

Commercial Preparation

Two methods of producing magnesium commercially are used. The principal method is the electrolysis of fused magnesium chloride, which is used in the extraction of magnesium from seawater (the principal source) and from dolomite. In recovery from seawater, the magnesium is precipitated as magnesium hydroxide by treatment with lime (calcium oxide) obtained from oyster shells. The hydroxide is collected and treated with hydrochloric acid to form the chloride. The chloride is fused and electrolyzed, forming magnesium metal and chlorine gas. The molten metal is cast into ingots for further processing; the chlorine gas is made into hydrochloric acid and is reused to form magnesium chloride. About 1 lb of magnesium is recovered from each 100 gal of seawater; the oceans are a virtually inexhaustible source of this metal. A second method of magnesium production, called the ferrosilicon process, involves the reduction of magnesium oxide (prepared by calcining dolomite) with an iron-silicon alloy.

Uses

Magnesium is a commercially important metal with many uses. It is only two thirds as dense as aluminum. It is easily machined, cast, forged, and welded. It is used extensively in alloys, chiefly with aluminum and zinc, and with manganese. Magnesium alloys were used as early as 1910 in Germany. Early structural uses of magnesium alloys were in aircraft fuselages, engine parts, and wheels. They are now also used in jet-engine parts, rockets and missiles, luggage frames, portable power tools, and cameras and optical instruments. Duralumin duralumin (drăl`yəmĭn, dy
..... Click the link for more information. and magnalium magnalium (măgnā`lēəm), alloy of aluminum and about 5% magnesium.
..... Click the link for more information. are alloys of magnesium. The metal is also used in pyrotechnics, especially in incendiary bombs, signals, and flares, and as a fuse for thermite thermite [from Thermit, a trade name], mixture of powdered or granular aluminum metal and powdered iron oxide. When ignited it gives off large amounts of heat. In wartime it has been used in incendiary bombs. A method for welding using thermite (invented by Dr.
..... Click the link for more information. . It is used in photographic flashbulbs and is added to some rocket and missile fuels. It is used in the preparation of malleable cast iron. An important use is in preventing the corrosion of iron and steel, as in pipelines and ship bottoms. For this purpose a magnesium plate is connected electrically to the iron. The rapid oxidation of the magnesium prevents the slower oxidation and corrosion of the iron.

magnesium

Chemical element, one of the alkaline earth metals, chemical symbol Mg, atomic number 12. The silvery white metal does not occur free in nature, but compounds such as the sulfate (Epsom salts), oxide (magnesia), and carbonate (magnesite) have long been known. The metal, which burns in air with a bright white light, is used in photographic flash devices, bombs, flares, and pyrotechnics; it is also a component of lightweight alloys for aircraft, spacecraft, cars, machinery, and tools. The compounds, in which it has valence 2, are used as insulators and refractories and in fertilizers, cement, rubber, plastics, foods, and pharmaceuticals (antacids, purgatives, laxatives). Magnesium is an essential element in human nutrition; it is the cofactor in enzymes of carbohydrate metabolism and in chlorophyll.