Structural Formula Vector Image
Title: Magnesium
CAS Registry Number: 7439-95-4
Literature References: Mg; at. wt 24.3050; at. no. 12; valence 2. Group IIA (2). Alkaline earth metal. One of the most common elements in the earth's crust: 27,640 ppm. Naturally occurring isotopes: 24 (78.99%); 25 (10.00%); 26 (11.01%). Known radioactive isotopes: 20-23, 27-34. Found naturally only in the form of its compounds in magnesite, carnallite, dolomite [CaMg(CO3)2], epsomite, kieserite, and many other minerals; found in sea-water, underground natural brines and salt deposits. Essential nutrient for most plant and animal life. Commercial production by electrolytic reduction of magnesium chloride or thermal reduction of magnesium oxide. First obtained in metallic form by Davy in 1808 by electrolyte reduction of magnesium oxide with mercury cathode. Prepn: Deville et al. in Gmelins, Magnesium (8th ed.) 27A, 121 (1937). Review of magnesium and its compounds: Goodenough, Stenger, "Magnesium, Calcium, Strontium, Barium and Radium" in Comprehensive Inorganic Chemistry vol. 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 591-664; Chemistry of the Elements N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 117-154; C. B. Wilson et al. in Kirk-Othmer Encyclopedia of Chemical Technology vol. 15 (Wiley-Interscience, New York, 4th ed., 1995) pp 622-674.
Properties: Silvery-white metal; hexagonal close-packed structure. Slowly oxidizes in moist air. Available as bars, ribbons, wire, castings, sheets and powder. mp 651°. bp 1100°. d20 1.738. Specific heat (20°) 0.245 cal/g. Heat of fusion 88 cal/g. Electrical resistivity 4.46 mohm-cm. E° (aq) Mg2+/Mg -2.37 V. Reacts very slowly with water at ordinary temp, less slowly at 100°. Reacts readily with dil acids with liberation of hydrogen; reacts with aq solns of ammonium salts, forming a double salt. Reduces carbon monoxide, carbon dioxide, sulfur dioxide, nitric oxide, and nitrous oxide at a red heat. Fine powder, thin sheets, chips and turnings are easily ignited and burn with intense heat and brilliant white flame. Combines directly with nitrogen, sulfur, the halogens, phosphorus, and arsenic. Reacts vigorously with anhydrous methyl alcohol.
Melting point: mp 651°
Boiling point: bp 1100°
Density: d20 1.738
CAUTION: Direct contact may cause irritation of skin, eyes, respiratory system. See: Fire Protection Guide to Hazardous Materials (National Fire Protection Assoc., Quincy, MA, 12th ed., 1997) Section 49, p 83.
Use: In alloys to produce light weight structural metals. In aluminum alloys to improve mechanical properties; in Grignard reagents; in dry cell batteries; in pyrotechnics. For hot metal desulfurization, esp. molten iron; prodn of ductile iron; metal reduction to produce elemental boron, titanium, zirconium; corrosion protection of steel structures; sacrificial anodes for corrosion protection.

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