Iron
Iron Atomic Number: 26
Iron Symbol: Fe
Iron Atomic Weight: 55.847
Iron Discovery: Known since prehistoric time
Electron Configuration: [Ar]4s23d6
Word Origin: Latin ferrum; Anglo-Saxon iron
Isotopes: There are 14 known isotopes of iron. Common iron consists of a mixture of 4 isotopes.
Properties: The melting point of iron is 1535°C, boiling point is 2750°C, specific gravity is 7.874 (20°C), with a valence of 2, 3, 4, or 6. Pure iron is chemically reactive and corrodes rapidly, especially in moist air or at elevated temperatures. Four allotropic forms, or ferrites, are known: a, b, g, and d, with transition points at 770, 928, and 1530°C. The a form is magnetic, but when iron is transformed into the b form, the magnetism disappears, although the lattice remains unchanged.
Uses: Iron is vital to plant and animal life. In humans, it appears in the hemoglobin molecule. Iron metal is usually alloyed with other metals and carbon for commercial uses. Pig iron is an alloy containing about 3-5% carbon, with varying quantities of Si, S, P, and Mn. Pig iron is brittle, hard, and fairly fusible and is used to produce other iron alloys, including steel. Wrought iron contains only a few tenths of a percent of carbon and is malleable, tough, and less fusible than pig iron. Wrought iron typically has a fibrous structure. Carbon steel is an iron alloy with carbon and small amounts of S, Si, Mn, and P. Alloy steels are carbon steels that contain additives such as chromium, nickel, vanadium, etc. Iron is the least expensive, most abundant, and most used of all metals.
Sources: Iron is a relatively abundant element in the universe. The sun and many types of stars contain iron in quantity. Iron is found native in a class of meteorites called siderites and it is a minor constituent of the other two classes of meteorites. The Earth's core is thought to be composed mainly of iron, with about 10% occluded hydrogen. Iron is the fourth most abundant element in the Earth's crust. The most common iron ore is hematite (Fe2O3), from which iron metal is obtained by reduction with carbon. Iron is also found in minerals such as taconite and magnetite, which is commonly seen as black sands along beaches and stream banks.
Element Classification: Transition Metal
Density (g/cc): 7.874
Appearance: malleable, ductile, silvery metal
Atomic Radius (pm): 126
Atomic Volume (cc/mol): 7.1
Covalent Radius (pm): 117
Ionic Radius: 64 (+3e) 74 (+2e)
Specific Heat (@20°C J/g mol): 0.443
Fusion Heat (kJ/mol): 13.8
Evaporation Heat (kJ/mol): ~340
Debye Temperature (K): 460.00
Pauling Negativity Number: 1.83
First Ionizing Energy (kJ/mol): 759.1
Oxidation States: 6, 3, 2, 0, -2
Lattice Structure: Body-Centered Cubic
Lattice Constant (Å): 2.870
Sources: hematite, magnetite(oxide)
Hydride(s): none
Oxide(s): FeO, Fe3O4, Fe2O3
Chloride(s): FeCl2, FeCl3
Reaction with Air: mild, =>Fe3O4
Reaction with 6M HCl: mild, =>H2, FeCl2
Reaction with 6M HCl: mild, =>H2, FeCl2
Reaction with 15M HNO3: passivated
Magnetic Ordering: ferromagnetic
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: 4.0
Vickers Hardness: 608 MPa
Brinell Hardness: 490 MPa
CAS Registry Number: 7439-89-6
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952)
Quiz: Ready to test your iron facts knowledge? Take the Iron Facts Quiz.
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