Chromium

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 whilk taks a heich polish, resists tarnishin, an haes a heich meltin pynt. The name o the element is derived frae the Greek wird χρῶμα, chrōma, meanin colour, acause mony o its compoonds is odious coloured.

Chromium, ₂₄Cr

Chromium
Appearance	sillery metallic
Standard atomic weight Ar, std(Cr)	7001519961000000000♠51.9961(6)
Chromium in the periodic cairt
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gowd Mercur (element) Thallium Leid (element) Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium - ↑ Cr ↓ Mo vanadium ← chromium → manganese
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, +4, +5, +6 (dependin on the oxidation state, an acidic, basic, or amphoteric oxide)
Electronegativity	Pauling scale: 1.66
Ionisation energies	(more)
Atomic radius	empirical: 128 pm
Covalent radius	139±5 pm
Colour lines in a spectral range Spectral lines o chromium
Ither 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)
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
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct 50Cr 4.345% >1.3×1018 y (β+β+) 50Ti 51Cr syn 27.7025 d ε 51V γ - 52Cr 83.789% stable 53Cr 9.501% stable 54Cr 2.365% stable
Decay modes in parentheses are predictit, but hae nae yet been observed

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.

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.