Iron

"Fe" redirects here. For other uses, see Fe (disambiguation).

manganese ← iron → cobalt - ↑ Fe ↓ Ru 26Fe Periodic table
Appearance
lustrous metallic with a grayish tinge Spectral lines of Iron
General properties
Name, symbol, number	iron, Fe, 26
Pronunciation	US /aɪ.ərn/; UK /ˈaɪərn/
Element category	transition metal
Group, period, block	8, 4, d
Standard atomic weight	55.845g·mol−1
Electron configuration	[Ar] 3d6 4s2
Electrons per shell	2, 8, 14, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	7.874 g·cm−3
Liquid density at m.p.	6.98 g·cm−3
Melting point	1811 K, 1538 °C, 2800 °F
Boiling point	3134 K, 2862 °C, 5182 °F
Heat of fusion	13.81 kJ·mol−1
Heat of vaporization	340 kJ·mol−1
Specific heat capacity	(25 °C) 25.10 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1728 1890 2091 2346 2679 3132
Atomic properties
Electronegativity	1.83 (Pauling scale)
Ionization energies (more)	1st: 762.5 kJ·mol−1
	2nd: 1561.9 kJ·mol−1
	3rd: 2957 kJ·mol−1
Atomic radius	126 pm
Covalent radius	132±3 (low spin), 152±6 (high spin) pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	ferromagnetic
	1043 K
Electrical resistivity	(20 °C) 96.1 nΩ·m
Thermal conductivity	(300 K) 80.4 W·m−1·K−1
Thermal expansion	(25 °C) 11.8 µm·m−1·K−1
Speed of sound (thin rod)	(r.t.) (electrolytic) 5120 m·s−1
Young's modulus	211 GPa
Shear modulus	82 GPa
Bulk modulus	170 GPa
Poisson ratio	0.29
Mohs hardness	4
Vickers hardness	608 MPa
Brinell hardness	490 MPa
CAS registry number	7439-89-6
Most stable isotopes
Main article: Isotopes of iron
iso NA half-life DM DE (MeV) DP 54Fe 5.8% >3.1×1022y 2ε capture  ? 54Cr 55Fe syn 2.73 y ε capture 0.231 55Mn 56Fe 91.72% 56Fe is stable with 30 neutrons 57Fe 2.2% 57Fe is stable with 31 neutrons 58Fe 0.28% 58Fe is stable with 32 neutrons 59Fe syn 44.503 d β− 1.565 59Co 60Fe syn 2.6×106 y β− 3.978 60Co
v • d • e

Iron ( /ˈaɪ.ərn/ or /ˈaɪərn/) is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is the most common element in the whole planet Earth, forming much of Earth's outer and inner core, and it is the fourth most common element in the Earth's crust. It is produced in abundance as a result of fusion in high-mass stars, where the production of nickel-56 (which decays to iron) is the last nuclear fusion reaction that is exothermic, becoming the last element to be produced before collapse of a supernova leads to events that scatter the precursor radionuclides of iron into space.
Like other Group 8 elements, iron exists in a wide range of oxidation states, −2 to + 6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give iron oxides, also known as rust. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion.
Iron metal has been used since ancient times, though lower-melting copper alloys were used first in history. Pure iron is soft (softer than aluminium), but is unobtainable by smelting. The material is significantly hardenened and strengthened by impurities from the smelting process, such as carbon. A certain proportion of carbon (between 0.2% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to cast iron. Further refinement with oxygen reduces the carbon content to make steel. Steels and low carbon iron alloys with other metals (alloy steels) are by far the most common metals in industrial use, due to their great range of desirable properties.
Iron chemical compounds, which include ferrous and ferric compounds, have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. It forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds, ferrocene was the first sandwich compound discovered.
Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen transport proteins in vertebrates. Iron is also the metal used at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals.