Iron

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MELTING POINT: 1,535°C
BOILING POINT: 2,750°C
DENSITY: 7.874 g/cm ³ (at 20°C)
MOST COMMON IONS: Fe ²⁺ , Fe ³⁺

Iron, believed to have been introduced on Earth by meteors, was found in Egyptian tombs dating from 3500 B.C.E. The Hittites (in the area known today as Turkey) smelted iron from ore around 1500 B.C.E. From ancient times to the present, the major use of iron has been in the production of steel.

Elemental iron, the major element in Earth's core, is the fourth most abundant element in Earth's crust (about 5.0% by mass overall, 0.5%–5% in soils, and approximately 2.5 parts per billion in seawater.) In the crust, iron is found mainly as the oxide minerals hematite, Fe ₂ O ₃ , and magnetite, Fe ₃ O ₄ . Other common mineral forms are siderite, FeCO ₃ , and various forms of FeO(OH). Iron is an essential element in almost all living organisms. In the human body, its concentration ranges between 3 and 380 parts per million (ppm) in bone, 380–450 ppm in blood, and 20–1,400 ppm in tissue.

Iron has a very stable nucleus and has fourteen known isotopes . Four isotopes, ⁵⁴ Fe (5.9%), ⁵⁶ Fe (91.72%), ⁵⁷ Fe (2.1%), and ⁵⁸ Fe (0.28%) make up essentially 100 percent of naturally occurring iron. Pure iron is a soft, white, lustrous metal . Elemental iron oxidizes in moist air but is stable in dry air. Finely divided elemental iron is pyrophoric. Iron dissolves in dilute mineral acid and in hot sodium hydroxide solution. Iron has seven oxidation states (−2, 0, +1, +2, +3, +4, and +6) with the +2, ferrous or Fe(II), and +3, ferric or Fe(III), states being the most common. With mild heating, iron reacts with the halogens and with sulfur, phosphorus, boron, carbon, and silicon to form a variety of compounds.

SEE ALSO Hemoglobin ; Industrial chemistry, Inorganic .

Douglas Cameron

Bibliography

Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; and Bochmann, Manfred (1999). Advanced Inorganic Chemistry: A Comprehensive Text, 6th edition. New York: Wiley.

Emsley, John (2001). Nature's Building Blocks: An A–Z Guide to the Elements. New York: Oxford University Press.

Lide, David R., ed. (1991). The CRC Handbook of Chemistry and Physics, 71st edition. Boca Raton, FL: CRC Press.