Frae Wikipedia, the free beuk o knawledge
Chromium, 24 Chromium Appearance sillery metallic Standard atomic weight A r, std (Cr) 7001519961000000000♠ 51.9961(6)[ 1] Chromium in the periodic cairt
Atomic nummer (Z ) 24 Group group 6 Period period 4 Block d-block Element category Transeetion metal Electron confeeguration [Ar ] 3d5 4s1 Electrons per shell 2, 8, 13, 1 Pheesical properties Phase at STP solit Meltin pynt 2180 K (1907 °C, 3465 °F) Bylin pynt 2944 K (2671 °C, 4840 °F) Density (near r.t. ) 7.19 g/cm3 when liquid (at m.p. ) 6.3 g/cm3 Heat o fusion 21.0 kJ/mol Heat o vapourisation 339.5 kJ/mol Molar heat capacity 23.35 J/(mol·K) Vapour pressur
P (Pa)
1
10
100
1 k
10 k
100 k
at T (K)
1656
1807
1991
2223
2530
2942
Atomic properties Oxidation states −4, −2, −1, 0, +1, +2 +3 +6 amphoteric oxide) Electronegativity Pauling scale: 1.66 Ionisation energies Atomic radius empirical: 128 pm Covalent radius 139±5 pm Colour lines in a spectral range Spectral lines o chromiumIther properties Naitural occurrence primordial Creestal structur body-centred cubic (bcc) Speed o soond thin rod 5940 m/s (at 20 °C) Thermal expansion 4.9 µm/(m·K) (at 25 °C) Thermal conductivity 93.9 W/(m·K) Electrical resistivity 125 n Ω·m (at 20 °C) Magnetic orderin AFM (rather: SDW [ 2] Young's modulus 279 GPa Shear modulus 115 GPa Bulk modulus 160 GPa Poisson ratio 0.21 Mohs haurdness 8.5 Vickers haurdness 1060 MPa Brinell haurdness 1120 MPa CAS Nummer 7440-47-3 History Diskivery Louis Nicolas Vauquelin (1797) First isolation Louis Nicolas Vauquelin (1798) Main isotopes o chromium
Decay modes in parentheses are predictit, but hae nae yet been observed | references
Chromium is a chemical element whilk haes the seembol Cr an atomic nummer 24. It is the first element in Group 6 . It is a steely-gray, lustrous , haurd an brickle metal [ 3] Greek wird χρῶμα, chrōma , meanin colour ,[ 4]
Ferrochromium alloy is commercially produced frae chromite bi silicothermic or aluminothermic reactions an chromium metal bi roastin an leachin processes follaed bi reduction wi caurbon an then aluminium . Chromium metal is o heich vailyie for its heich corrosion resistance an haurdness . A major development in steel production wis the diskivery that steel coud be made heichly resistant tae corrosion an discolouration bi addin metallic chromium tae form stainless steel . Stainless steel an chrome platin (electroplatin wi chromium) thegither comprise 85% o the commercial uise.
Trivalent chromium (Cr(III)) ion is an essential nutrient in trace amoonts in humans for insulin , succar an lipid metabolism , awtho the issue is debatit.[ 5]
While chromium metal an Cr(III) ions are nae conseedert toxic, hexavalent chromium (Cr(VI)) is toxic an carcinogenic . Abandont chromium production steids eften require environmental cleanup .
↑ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)" . Pure and Applied Chemistry 88 (3): 265–91. doi :10.1515/pac-2015-0305 ↑ 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 . ↑ Brandes, E. A.; Greenaway, H. T.; Stone, H. E. N. (1956). "Ductility in Chromium". Nature . 178 (587): 587. Bibcode :1956Natur.178..587B . doi :10.1038/178587a0 . ↑ 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 Juin 2016 .
