Iron is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. It is a metal in the first transition series. Like other group 8 elements, it exists in a wide range of oxidation states. Iron and iron alloys (steels) are by far the most common metals and the most common ferromagnetic materials in everyday use. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in air.
Iron is the most common element in the earth as a whole, and the fourth most common in the earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used metal, and iron compounds, which include ferrous and ferric compounds, have several uses as well.
Iron has been used since ancient times, though not as early as bronze or the other copper related alloys. Iron is ubiquitous in modern life; it is used primarily for its structural strength. Pure iron is soft (softer than aluminium), but the material is significantly strengthened by addition of minute amounts of impurities, such as carbon. Alloying iron with appropriate small amounts (up to a few per cent) of other metals and carbon produces steel, which can be 1,000 times harder than pure iron. Iron is smelted in a blast furnace, where ore is reduced by coke to metallic iron.
Elemental iron is reactive; it oxidizes in air to give iron oxides, also known as rust. The rusting of iron and iron alloys is undesirable, and has a major economic impact. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron itself. Thus, iron oxides flake off and expose fresh surfaces for corrosion.
Iron exists from oxidation state −2 to + 6, although +2 and +3 are the most common. It forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds, ferrocene is significant as the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with dioxygen as hemoglobin and myoglobin; these two compounds are common oxygen transport proteins in vertebrates.
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