Back Chroom Afrikaans ክሮሚየም Amharic Cromo AN كروم Arabic كروم ARY كروم ARZ Cromu (elementu) AST Vogel AVK क्रोमियम AWA Xrom Azerbaijani
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| Chromium | ||||||||||||||||||||||||||||||||||||||
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| Appearance | silvery metallic | |||||||||||||||||||||||||||||||||||||
| Standard atomic weight Ar°(Cr) | ||||||||||||||||||||||||||||||||||||||
| Chromium in the periodic table | ||||||||||||||||||||||||||||||||||||||
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| Atomic number (Z) | 24 | |||||||||||||||||||||||||||||||||||||
| Group | group 6 | |||||||||||||||||||||||||||||||||||||
| Period | period 4 | |||||||||||||||||||||||||||||||||||||
| Block | d-block | |||||||||||||||||||||||||||||||||||||
| Electron configuration | [Ar] 3d5 4s1 | |||||||||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 13, 1 | |||||||||||||||||||||||||||||||||||||
| Physical properties | ||||||||||||||||||||||||||||||||||||||
| Phase at STP | solid | |||||||||||||||||||||||||||||||||||||
| Melting point | 2180 K (1907 °C, 3465 °F) | |||||||||||||||||||||||||||||||||||||
| Boiling point | 2944 K (2671 °C, 4840 °F) | |||||||||||||||||||||||||||||||||||||
| Density (at 20° C) | 7.192 g/cm3 [3] | |||||||||||||||||||||||||||||||||||||
| when liquid (at m.p.) | 6.3 g/cm3 | |||||||||||||||||||||||||||||||||||||
| Heat of fusion | 21.0 kJ/mol | |||||||||||||||||||||||||||||||||||||
| Heat of vaporization | 347 kJ/mol | |||||||||||||||||||||||||||||||||||||
| Molar heat capacity | 23.35 J/(mol·K) | |||||||||||||||||||||||||||||||||||||
Vapor pressure
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| Atomic properties | ||||||||||||||||||||||||||||||||||||||
| Oxidation states | −4, −2, −1, 0, +1, +2, +3, +4, +5, +6 (depending on the oxidation state, an acidic, basic, or amphoteric oxide) | |||||||||||||||||||||||||||||||||||||
| Electronegativity | Pauling scale: 1.66 | |||||||||||||||||||||||||||||||||||||
| Ionization energies |
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| Atomic radius | empirical: 128 pm | |||||||||||||||||||||||||||||||||||||
| Covalent radius | 139±5 pm | |||||||||||||||||||||||||||||||||||||
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| Other properties | ||||||||||||||||||||||||||||||||||||||
| Natural occurrence | primordial | |||||||||||||||||||||||||||||||||||||
| Crystal structure | body-centered cubic (bcc) (cI2) | |||||||||||||||||||||||||||||||||||||
| Lattice constant |  | |||||||||||||||||||||||||||||||||||||
| Thermal expansion | 4.81×10−6/K (at 20 °C)[3] | |||||||||||||||||||||||||||||||||||||
| Thermal conductivity | 93.9 W/(m⋅K) | |||||||||||||||||||||||||||||||||||||
| Electrical resistivity | 125 nΩ⋅m (at 20 °C) | |||||||||||||||||||||||||||||||||||||
| Magnetic ordering | antiferromagnetic (rather: SDW)[4] | |||||||||||||||||||||||||||||||||||||
| Molar magnetic susceptibility | +280.0×10−6 cm3/mol (273 K)[5] | |||||||||||||||||||||||||||||||||||||
| Young's modulus | 279 GPa | |||||||||||||||||||||||||||||||||||||
| Shear modulus | 115 GPa | |||||||||||||||||||||||||||||||||||||
| Bulk modulus | 160 GPa | |||||||||||||||||||||||||||||||||||||
| Speed of sound thin rod | 5940 m/s (at 20 °C) | |||||||||||||||||||||||||||||||||||||
| Poisson ratio | 0.21 | |||||||||||||||||||||||||||||||||||||
| Mohs hardness | 8.5 | |||||||||||||||||||||||||||||||||||||
| Vickers hardness | 1060 MPa | |||||||||||||||||||||||||||||||||||||
| Brinell hardness | 687–6500 MPa | |||||||||||||||||||||||||||||||||||||
| CAS Number | 7440-47-3 | |||||||||||||||||||||||||||||||||||||
| History | ||||||||||||||||||||||||||||||||||||||
| Discovery and first isolation | Louis Nicolas Vauquelin (1794, 1797) | |||||||||||||||||||||||||||||||||||||
| Isotopes of chromium | ||||||||||||||||||||||||||||||||||||||
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Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.[7]
Chromium metal is valued for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating (electroplating with chromium) together comprise 85% of the commercial use. Chromium is also greatly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, and almost 90% of infrared light.[8] The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color,[9] because many chromium compounds are intensely colored.
Industrial production of chromium proceeds from chromite ore (mostly FeCr2O4) to produce ferrochromium, an iron-chromium alloy, by means of aluminothermic or silicothermic reactions. Ferrochromium is then used to produce alloys such as stainless steel. Pure chromium metal is produced by a different process: roasting and leaching of chromite to separate it from iron, followed by reduction with carbon and then aluminium.
In the United States, trivalent chromium (Cr(III)) ion is considered an essential nutrient in humans for insulin, sugar, and lipid metabolism.[10] However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was insufficient evidence for chromium to be recognized as essential.[11]
While chromium metal and Cr(III) ions are considered non-toxic, hexavalent chromium, Cr(VI), is toxic and carcinogenic. According to the European Chemicals Agency (ECHA), chromium trioxide that is used in industrial electroplating processes is a "substance of very high concern" (SVHC).[12]
Abandoned chromium production sites often require environmental cleanup.[13]
- ^ "Standard Atomic Weights: Chromium". CIAAW. 1983.
- ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
- ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
- ^ Fawcett, Eric (1988). "Spin-density-wave antiferromagnetism in chromium". Reviews of Modern Physics. 60: 209. Bibcode:1988RvMP...60..209F. doi:10.1103/RevModPhys.60.209.
- ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
- ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
- ^ Brandes, EA; Greenaway, HT; Stone, HEN (1956). "Ductility in Chromium". Nature. 178 (4533): 587. Bibcode:1956Natur.178..587B. doi:10.1038/178587a0. S2CID 4221048.
- ^ Coblentz, WW; Stair, R. "Reflecting power of beryllium, chromium, and several other metals" (PDF). National Institute of Standards and Technology. NIST Publications. Retrieved 11 October 2018.
- ^ χρῶμα, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- ^ "Chromium". Office of Dietary Supplements, US National Institutes of Health. 2016. Retrieved 26 June 2016.
- ^ "Scientific Opinion on Dietary Reference Values for chromium". European Food Safety Authority. 18 September 2014. Retrieved 20 March 2018.
- ^ "Substance Information - ECHA". echa.europa.eu. Retrieved 17 January 2022.
- ^ EPA (August 2000). "Abandoned Mine Site Characterization and Cleanup Handbook" (PDF). United States Environmental Protection Agency. Retrieved 8 September 2019.