Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth’s outer and inner core. It is the fourth most common element in the Earth’s crust.
Discovery and History
The first signs of use of iron come from artifacts of the Sumerians and Egyptians dated to around 4000 B.C.E. They prepared tips of spears, daggers, and ornaments from iron recovered from meteorites. Because meteorites fall from the sky, some linguists have conjectured that the English word iron (Old English īsern), which has cognates in many northern and western European languages, derives from the Etruscan aisar, which means “the gods”. Some have linked the iron in meteorites to a verse in the Quran(57:25) that says, “… and We sent down iron in which is incredible strength and many benefits for mankind.” Iron objects have been found in Egypt around 3500 BC. They contain about 7.5% nickel, which indicates that they were of meteoric origin. The ancient Hittites of Asia Minor, today’s Turkey, were the first to smelt iron from its ores around 1500 BC and this new, stronger, metal gave them economic and political power.
|Periodic Table Classification||Group 8
|State at 20C||Solid|
|Color||Metallic - gray|
|Electron Configuration||[Ar] 3d6 4s2|
|Electron Shell|| 2, 8, 14, 2
|Density||7.87 g.cm-3 at 20°C|
|Atomic Mass||55.84 g.mol -1|
|Electronegativity according to Pauling||1.83|
Iron is an abundant element in the universe; it is found in many stars, including the sun. Iron is the fourth most abundant element in the earth’s crust, of which it constitutes about 5% by weight, and is believed to be the major component of the earth’s core. Iron is found distributed in the soil in low concentrations and is found dissolved in ground water and the ocean to a limited extent. It is rarely found uncombined in nature except in meteorites, but iron ores and minerals are abundant and widely distributed .
The principal ores of iron are hematite (ferric oxide, Fe 2O 3) and limonite (ferric oxide trihydrate, Fe 2O 3·3H 2O). Other ores include siderite (ferrous carbonate, FeCO 3), taconite (an iron silicate), and magnetite (ferrous-ferric oxide, Fe 3O 4), which often occurs as a white sand. Iron pyrite (iron disulfide, FeS 2) is a crystalline gold-colored mineral known as fool’s gold. Chromite is a chromium ore that contains iron. Lodestone is a form of magnetite that exhibits natural magnetic properties . Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.
The Latin name for iron is ferrum, which is the source of its atomic symbol, Fe atomic number 26; atomic weight 55.845; melting point about 1,535°C; boiling point about 2,750°C and specific gravity of 7.87 at 20°C. Like the other group 8 elements, iron exists in a wide range of oxidation states, −2 to +7, although +2 and +3 are the most common. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust.
In chemical terms, it is classified as a transition metal. It is located in period 4 of the periodic table, situated between manganese and cobalt. In addition, it lies at the top of group 8 (former group 8B). Iron, cobalt, and nickel have a number of similar properties and were once grouped together as group 8B . Iron has the ability to form variable oxidation states differing by steps of one and a very large coordination and organometallic chemistry.
Significance and Uses
- Iron (III) oxide: ferric oxide, or red iron oxide (Fe2O3): This compound corresponds to iron rust. Its mineral form, known as hematite, is mined as the main ore of iron and is used in the production of iron in a blast furnace.
- Iron (III) oxide-hydroxide, hydrated iron oxide, or yellow iron oxide (FeO(OH)): This solid material has colors ranging from yellow through dark brown to black. It occurs naturally as minerals goethite, feroxyhyte, limonite, and lepidocrocite. It is used in aquarium water treatment as a phosphate binder.
- Iron (II) sulfate or ferrous sulfate (FeSO4): It is commonly used additive that is found in various foods. Ferrous sulphate is used to treat anemia (iron-deficiency).
- The most common use of iron is in manufacturing of steel, that has various attractive properties and uses.
- Cast iron (with 3-5% carbon) is used for making pumps, pipes and valves.
- Iron and steel are widely used in civil engineering and construction.
Iron can be found in meat, whole meal products, potatoes and vegetables. The human body absorbs iron in animal products faster than iron in plant products. Iron may cause conjunctivitis, choroiditis, and retinitis if it contacts and remains in the tissues. Chronic inhalation of excessive concentrations of iron oxide fumes or dusts may result in development of a benign pneumoconiosis, called siderosis. Inhalation of excessive concentrations of iron oxide may enhance the risk of lung cancer development in workers exposed to pulmonary carcinogens .
Isotopes of Iron
Naturally occurring iron consists of four isotopes: 5.85 percent of slightly radioactive 54Fe (half-life >3.1×1022 years), 91.75 percent of stable 56Fe, 2.12 percent of stable 57Fe, and 0.28 percent of stable 58Fe. In addition, it appears that the naturally occurring radioactive isotope 60Fe, with a half-life of 1.5 million years, is now extinct, but it can be produced synthetically. Much of the past work on measuring the isotopic composition of iron centered on determining 60Fe variations due to processes accompanying nucleosynthesis (that is, through meteorite studies) and ore formation.
1. Rick McCallister and Silvia McCallister-Castillo, A-AL Etruscan Glossary (1999). Retrieved October 22, 2011.