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. 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. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, 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. 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. 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). Abandoned chromium production sites often require environmental cleanup.

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Atomic properties

Standard atomic weight51.9961 ±6·10-4
Atomic mass51.9961 u

Atomic radii

Radius (empirical)128 pm
Radius (calculated)166 pm
Covalent radius139 ±5 pm

Atomic shell

Electron configurationAr 3d5 4s1
Ionization energy(1st) 6.76651 eV
(2nd) 16.486305 eV
(3rd) 30.959 eV
(4th) 49.16 eV
(5th) 69.46 eV
Shell model

Physical properties

Density7.14 g·cm−3 (293.1 K)
Molar volume7.23·10-6 m3·mol−1
Speed of sound5,940 m·s−1 (293.1 K)


Melting point2,180 K
Boiling point2,944 K
Liquid range764 K
Transition temperature3 K


Melting enthalpy20.5 kJ·mol-1
Enthalpy of vaporization339 kJ·mol-1
Binding energy397 kJ·mol-1

Heat and conductivity

Specific heat capacity449 J·kg−1·K−1
Thermal conductivity94 W·m-1·K-1
Expansion coefficient4.899·10-6 K-1
Work function4.5 eV


Mohs hardness8.5
Brinell hardness1,120 NM·m-2
Vickers hardness1,060 NM·m-2

Elastic properties

Young’s modulus279 GPa
Shear modulus115 GPa
Bulk modulus160 GPa
Poisson’s ratio0.21

Electrical properties

Electrical conductivity7.87·106 S·m-1
Resistance1.27·10-7 Ωm


Magnetic susceptibility2.8·10-4 cm3·mol−1 (273 K)

Chemical properties

Basicitystrongly acidic
Oxidation state6, 3, 2, 1
Standard potential-0.744 V (Cr3+ + 3e- → Cr)


Pauling scale1.66
Sanderson scale1.66
Allred-Rochow scale1.56
Ghosh-Gupta scale3.295 eV
Nagle scale1.29
Pearson absolute negativity3.72 eV

Other properties

Natural occurrenceprimordial
Crystal structureBody-centered cubic
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature under special conditions
Price/kg9.4 USD

Natural abundances

15,000 ppb ≈ 1.5·1014 M☉
20,000 ppb ≈ 3.97·1013 Mt
3.1·106 ppb ≈ 3.1 kg
Earth’s crust
140,000 ppb ≈ 3.87·106 Mt
0.6 ppb ≈ 822 kt
Flowing water
1 ppb ≈ 16 kt
Human body
30 ppb ≈ 2.1 mg