iron

iron
Atomic number	26
Standard atomic weight	55.845
Category	transition metal
Appearance	lustrous metallic with a grayish tinge
Phase at STP	solid
Melting point C	1538
Boiling point C	2862
Density g cm3	7.874
Heat of fusion	13.81
Heat of vaporization	340
Molar heat capacity	25.10
First ionization	762.5
Second ionization	1561.9
Third ionization	2957
Oxidation states	−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7
Electronegativity	1.83
Atomic radius	126
Covalent radius	132±3
Crystal structure	body-centered cubic (bcc)
Speed of sound thin rod	5120
Thermal expansion	11.8
Thermal conductivity	80.4
Electrical resistivity	96.1
Young's modulus	211
Shear modulus	82
Bulk modulus	170
Poisson ratio	0.29
Vickers hardness	608
Brinell hardness	200–1180
CAS number	7439-89-6

iron. A lustrous, silver-gray metal, it is the fourth most abundant element in the Earth's crust and the most common element by mass on our planet overall, forming much of Earth's outer and inner core. This transition metal is renowned for its strength, magnetic properties, and its pivotal role in the development of human civilization, particularly through its alloys like steel. Its chemical symbol, Fe, originates from the Latin word *ferrum*, and it is essential to numerous biological processes, including oxygen transport in vertebrate blood.

Properties

It is a metal in the first transition series of the periodic table, exhibiting typical metallic properties such as high tensile strength, malleability, and good thermal and electrical conductivity. It is ferromagnetic at room temperature, a property famously utilized in compass needles and electric motor cores, though it loses this magnetism above its Curie temperature of 770 °C. The element has four stable isotopes, with ⁵⁶Fe being the most abundant, and crystallizes in a body-centered cubic structure at standard conditions, transforming to a face-centered cubic austenite phase at high temperatures. Its reactivity is significant, readily forming iron oxide when exposed to oxygen and water, a process known as rusting, which is accelerated by the presence of salts, as seen in marine environments like the North Atlantic.

Occurrence and production

While native metallic forms are rare, found occasionally in basalt or from meteorite impacts like the Canyon Diablo meteorite, it is primarily obtained from iron ores such as hematite (Fe₂O₃) and magnetite (Fe₃O₄). Major global deposits are mined in the Pilbara region of Australia, the Iron Quadrangle in Brazil, and around Lake Superior in the United States. The dominant industrial process is the blast furnace, where ore is reduced with coke in the presence of limestone to produce pig iron, which is then further refined into steel through processes like the basic oxygen furnace or the electric arc furnace. Alternative methods include direct reduced iron production, used in facilities like those operated by Midrex Technologies.

History

Its use defines entire archaeological ages, with the Iron Age succeeding the Bronze Age in most regions, beginning around 1200 BCE in the Ancient Near East, notably among the Hittites. Early smelting techniques using bloomery furnaces were developed independently in Sub-Saharan Africa, such as by the Nok culture, and in China during the Zhou dynasty. The production of crucible steel was advanced in India and Sri Lanka, creating famed Damascus steel, while the Industrial Revolution was fueled by innovations like Abraham Darby I's coke-fired furnace at Coalbrookdale and Henry Bessemer's converter, which enabled mass production. The element's cultural significance is profound, being used in everything from the Eiffel Tower to the swords of the Vikings.

Applications

Its primary use is in the form of steel, an alloy with carbon, which is fundamental to modern infrastructure, including skyscrapers, bridges like the Golden Gate Bridge, railway networks, and automobile manufacturing. Cast iron, with higher carbon content, is used for engine blocks, pipes, and cookware, such as products from Lodge Manufacturing Company. Other important alloys include stainless steel, which contains chromium and resists corrosion, used in surgical instruments and the Chrysler Building, and high-strength alloys used in tank armor and NASA spacecraft. Magnets made from its compounds are essential in loudspeakers, hard disk drives, and MRI scanners in hospitals.

Biological role

It is an essential nutrient for almost all living organisms, playing a central role in oxygen transport and storage through proteins like hemoglobin in red blood cells and myoglobin in muscle tissue. In cells, it is a key component of cytochromes in the electron transport chain, crucial for cellular respiration and ATP production. Its homeostasis in the human body is tightly regulated by proteins like ferritin for storage and transferrin for transport; dysregulation can lead to disorders such as hemochromatosis or anemia. Plants require it for chlorophyll synthesis and various enzyme functions, with deficiencies causing chlorosis.

Chemical compounds

It forms a vast array of compounds, most commonly in the +2 and +3 oxidation states. Iron(II) oxide (FeO) and iron(III) oxide (Fe₂O₃) are important pigments and industrial materials, with the latter giving Mars its characteristic red color. Iron sulfate is used in water treatment and as a nutritional supplement, while iron chloride acts as a catalyst in organic reactions like the Friedel–Crafts reaction. Prussian blue (Fe₄[Fe(CN)₆]₃), one of the first synthetic pigments, is used in blueprints and as an antidote for thallium poisoning. Complex organometallic compounds, such as ferrocene, are foundational in organometallic chemistry and catalysis.

Category:Chemical elements Category:Transition metals Category:Dietary minerals