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Chromium,  24Cr
General properties
Name, symbol Chromium, Cr
Appearance Silvery metallic
Chromium in the periodic table


Atomic number 24
Standard atomic weight (Ar) 51.9961(6)
Group, block , d-block
Period period 4
Electron configuration [Ar] 3d5 4s1
per shell
2, 8, 13, 1
Physical properties
Silvery metallic
Phase Solid
Melting point 2180 K ​(1907 °C, ​​3465 °F)
Boiling point 2944 K ​(2671 °C, ​​4840 °F)
Density near r.t. 7.19 g/cm3
when liquid, at  6.3 g/cm3
Heat of fusion 21.0 kJ/mol
Heat of 347 kJ/mol
Molar heat capacity 23.35 J/(mol·K)
Atomic properties
Oxidation states 6, 5, 4, 3, 2, 1, −1, −2, −4 ​(depending on the oxidation state, an acidic, basic, or amphoteric oxide)
Electronegativity Pauling scale: 1.66
energies 1st: 652.9 kJ/mol
2nd: 1590.6 kJ/mol
3rd: 2987 kJ/mol
Atomic radius empirical: 128 pm
Covalent radius 139±5 pm
Crystal structure ​Body-centered cubic (bcc)
Speed of sound 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 125·10-9 Ω·m (at 20 °C)
Magnetic ordering Antiferromagnetic
Young's modulus 279 GPa
Shear modulus 115 GPa
Bulk modulus 160 GPa
Poisson ratio 0.21
Mohs hardness 8.5
Vickers hardness 1060 MPa
Brinell hardness 687–6500 MPa
CAS Registry Number 7440-47-3
Discovery and first isolation Louis Nicolas Vauquelin (1797-1798)
· references

Chromium is a transition metal with the symbol Cr and atomic number 24.



Chromium metal is quite unreactive. It tends to form a thin passivation layer of chromium(III) oxide, which prevents further oxidation. Nitric acid can enhance this passivation layer, but reducing agents tend to destroy it.

Most chromium compounds are amphoteric.


Chromium is a shiny silver color and is quite hard and brittle. It is antiferromagnetic at room temperature, and is the only element that exhibits this property at such high temperatures. Chromium metal has a high melting point of 1907 °C and boils at 2671 °C. It has a density of 7.19 g/cm3


Pure chromium metal is hard to find, as it tends to be alloyed with different metals. Chromoly, which consists of iron, chromium and molybdenum, tends to have a relatively high concentration of chromium compared to other alloys. Stainless steel is another option.

Chromium makes up 10% or more of stainless steel, a very accessible metal to the home chemist. See Preparation for extraction of chromium from this.


Aluminothermic reactions (thermites) with chromium(III) oxide may form chromium metal.

Chromium hydroxide can be produced from stainless steel by first dissolving the metal in hot hydrochloric acid. Iron can be precipitated out as iron(III) sulfate by reacting the resulting solution with sulfuric acid or sodium sulfate in a heated, oxidative environment. With the precipitate filtered out, chromium hydroxide can finally be precipitated from the solution using ammonia, sodium hydroxide, or sodium carbonate. An excess of ammonia or sodium hydroxide will dissolve the precipitate, again, so a nearly stoichiometric amount is recommended. The final product has some iron contamination as well.




Bulk chromium has good chemical resistivity and isn't known to cause contact dermatitis. Chromium(III) is known to be an essential trace element in the organism. Studies done so far have not shown whether Cr(III) poses any toxic or mutagenic properties, as the results are inconclusive.

Hexavalent chromium on the other hand is a known carcinogenic.


Bulk chromium does not require special storage, though it should be kept away from any halogens and mineral acid vapors.


Chromium and Cr(III) pose little toxicity to the environment, though it's best to avoid dumping them in the environment.

Hexavalent chromium must be reduced to Cr(III) before disposal. This is done with a reducing agent, sulfites of metabisulfites should do the trick.


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