Chromium

  • chromium, 24cr
    chromium crystals and 1cm3 cube.jpg
    chromium
    appearancesilvery metallic
    standard atomic weight ar, std(cr)51.9961(6)[1]
    chromium in the periodic table
    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 iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
    rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver 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 gold mercury (element) thallium lead 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 nihonium flerovium moscovium livermorium tennessine oganesson


    cr

    mo
    vanadiumchromiummanganese
    atomic number (z)24
    groupgroup 6
    periodperiod 4
    blockd-block
    element category  transition metal
    electron configuration[ar] 3d5 4s1
    electrons per shell2, 8, 13, 1
    physical properties
    phase at stpsolid
    melting point2180 k ​(1907 °c, ​3465 °f)
    boiling point2944 k ​(2671 °c, ​4840 °f)
    density (near r.t.)7.19 g/cm3
    when liquid (at m.p.)6.3 g/cm3
    heat of fusion21.0 kj/mol
    heat of vaporization347 kj/mol
    molar heat capacity23.35 j/(mol·k)
    vapor pressure
    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 (depending on the oxidation state, an acidic, basic, or amphoteric oxide)
    electronegativitypauling scale: 1.66
    ionization energies
    • 1st: 652.9 kj/mol
    • 2nd: 1590.6 kj/mol
    • 3rd: 2987 kj/mol
    • (more)
    atomic radiusempirical: 128 pm
    covalent radius139±5 pm
    color lines in a spectral range
    spectral lines of chromium
    other properties
    natural occurrenceprimordial
    crystal structurebody-centered cubic (bcc)
    body-centered cubic crystal structure for chromium
    speed of sound thin rod5940 m/s (at 20 °c)
    thermal expansion4.9 µm/(m·k) (at 25 °c)
    thermal conductivity93.9 w/(m·k)
    electrical resistivity125 nΩ·m (at 20 °c)
    magnetic orderingantiferromagnetic (rather: sdw)[2]
    magnetic susceptibility+280.0·10−6 cm3/mol (273 k)[3]
    young's modulus279 gpa
    shear modulus115 gpa
    bulk modulus160 gpa
    poisson ratio0.21
    mohs hardness8.5
    vickers hardness1060 mpa
    brinell hardness687–6500 mpa
    cas number7440-47-3
    history
    discovery and first isolationlouis nicolas vauquelin (1794, 1797)
    main isotopes of chromium
    iso­tope abun­dance half-life (t1/2) decay mode pro­duct
    50cr 4.345% stable
    51cr syn 27.7025 d ε 51v
    γ
    52cr 83.789% stable
    53cr 9.501% stable
    54cr 2.365% stable
    category category: chromium
    | references

    chromium is a chemical element with the 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.[4] chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. chromium is also highly valued as a metal that is able to be highly polished while resisting tarnishing. polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light being reflected.[5] the name of the element is derived from the greek word χρῶμα, chrōma, meaning color,[6] because many chromium compounds are intensely colored.

    ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and then aluminium. chromium metal is of high value 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.

    in the united states, trivalent chromium (cr(iii)) ion is considered an essential nutrient in humans for insulin, sugar and lipid metabolism.[7] however, in 2014, the european food safety authority, acting for the european union, concluded that there was not sufficient evidence for chromium to be recognized as essential.[8]

    while chromium metal and cr(iii) ions are not considered toxic, hexavalent chromium (cr(vi)) is both toxic and carcinogenic. abandoned chromium production sites often require environmental cleanup.[9]

  • physical properties
  • chemistry and compounds
  • occurrence
  • history
  • production
  • applications
  • biological role
  • precautions
  • see also
  • notes
  • references
  • bibliography
  • external links

Chromium, 24Cr
Chromium crystals and 1cm3 cube.jpg
Chromium
Appearancesilvery metallic
Standard atomic weight Ar, std(Cr)51.9961(6)[1]
Chromium in the periodic table
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 Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver 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 Gold Mercury (element) Thallium Lead 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 Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Cr

Mo
vanadiumchromiummanganese
Atomic number (Z)24
Groupgroup 6
Periodperiod 4
Blockd-block
Element category  Transition metal
Electron configuration[Ar] 3d5 4s1
Electrons per shell2, 8, 13, 1
Physical properties
Phase at STPsolid
Melting point2180 K ​(1907 °C, ​3465 °F)
Boiling point2944 K ​(2671 °C, ​4840 °F)
Density (near r.t.)7.19 g/cm3
when liquid (at m.p.)6.3 g/cm3
Heat of fusion21.0 kJ/mol
Heat of vaporization347 kJ/mol
Molar heat capacity23.35 J/(mol·K)
Vapor pressure
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 (depending on the oxidation state, an acidic, basic, or amphoteric oxide)
ElectronegativityPauling scale: 1.66
Ionization energies
  • 1st: 652.9 kJ/mol
  • 2nd: 1590.6 kJ/mol
  • 3rd: 2987 kJ/mol
  • (more)
Atomic radiusempirical: 128 pm
Covalent radius139±5 pm
Color lines in a spectral range
Spectral lines of chromium
Other properties
Natural occurrenceprimordial
Crystal structurebody-centered cubic (bcc)
Body-centered cubic crystal structure for chromium
Speed of sound thin rod5940 m/s (at 20 °C)
Thermal expansion4.9 µm/(m·K) (at 25 °C)
Thermal conductivity93.9 W/(m·K)
Electrical resistivity125 nΩ·m (at 20 °C)
Magnetic orderingantiferromagnetic (rather: SDW)[2]
Magnetic susceptibility+280.0·10−6 cm3/mol (273 K)[3]
Young's modulus279 GPa
Shear modulus115 GPa
Bulk modulus160 GPa
Poisson ratio0.21
Mohs hardness8.5
Vickers hardness1060 MPa
Brinell hardness687–6500 MPa
CAS Number7440-47-3
History
Discovery and first isolationLouis Nicolas Vauquelin (1794, 1797)
Main isotopes of chromium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
50Cr 4.345% stable
51Cr syn 27.7025 d ε 51V
γ
52Cr 83.789% stable
53Cr 9.501% stable
54Cr 2.365% stable
Category Category: Chromium
| references

Chromium is a chemical element with the 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.[4] Chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. Chromium is also highly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light being reflected.[5] The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color,[6] because many chromium compounds are intensely colored.

Ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and then aluminium. Chromium metal is of high value 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.

In the United States, trivalent chromium (Cr(III)) ion is considered an essential nutrient in humans for insulin, sugar and lipid metabolism.[7] However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was not sufficient evidence for chromium to be recognized as essential.[8]

While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium (Cr(VI)) is both toxic and carcinogenic. Abandoned chromium production sites often require environmental cleanup.[9]