Cr
51.996Chromium
Krom
Chromium is a hard transition metal with atomic number 24. It is essential to stainless steel, chrome plating and pigments, and it is famous for the electron configuration exception [Ar] 3d⁵ 4s¹ and colorful chromium compounds.
24
51.996 g/mol
[Ar] 3d⁵ 4s¹
2 | 8 | 13 | 1
1.66
7.19 g/cm³
1906.8 °C
2670.8 °C
Louis-Nicolas Vauquelin
Chromium was discovered by Louis-Nicolas Vauquelin in 1797 in the mineral crocoite. Its name comes from the Greek chroma, meaning color, because chromium compounds produce many bright colors.
Chromium-52
Natural abundance: About 83.8%. The most abundant stable isotope of chromium.Chromium-53
Natural abundance: About 9.5%. Stable isotope used in isotope and NMR studies.Chromium-50
Natural abundance: About 4.35%. Stable isotope of chromium.Chromium-54
Natural abundance: About 2.36%. Stable isotope of chromium.Cr₂O₃
Chromium(III) OxideGreen pigment, polishing compound and source of chromium color in some gemstones.CrO₃
Chromium TrioxideStrong oxidizer used in chromium plating and laboratory oxidation chemistry.K₂Cr₂O₇
Potassium DichromateOrange oxidizing agent used in analytical chemistry and historical laboratory tests.K₂CrO₄
Potassium ChromateYellow chromate salt used in precipitation and indicator chemistry.PbCrO₄
Lead ChromateChrome yellow pigment, now restricted in many uses due to lead toxicity.- Stainless steel, where chromium forms a protective Cr₂O₃ passive film
- Chrome plating for shiny, corrosion-resistant surfaces
- Chromium pigments such as chrome green and historical chrome yellow
- Refractory chromite materials for high-temperature furnaces
- Strong oxidizing reagents such as dichromates in analytical and industrial chemistry
Chromium(III) has been discussed in connection with glucose metabolism, but its essential role in humans remains debated. Hexavalent chromium, chromium(VI), is toxic and carcinogenic, so oxidation state is crucial when discussing chromium safety.
- Chromium’s name comes from color, and chromium compounds can be green, blue, yellow, orange or red.
- Stainless steel resists rust because chromium forms a thin self-healing oxide film.
- Chromium has the important electron configuration exception [Ar] 3d⁵ 4s¹.
- Ruby and emerald colors can both involve chromium ions in different crystal environments.
- Chromium has atomic number 24 and belongs to group 6.
- Its electron configuration is [Ar] 3d⁵ 4s¹, not [Ar] 3d⁴ 4s².
- Common oxidation states include +2, +3 and +6.
- Chromium(VI) compounds are much more hazardous than many chromium(III) compounds, so oxidation state matters.
What is the atomic number of chromium?
The atomic number of chromium is 24.
What is the electron configuration of chromium?
Chromium has the electron configuration [Ar] 3d⁵ 4s¹.
Why is chromium an electron configuration exception?
Chromium places one 4s electron into the 3d subshell because the half-filled 3d⁵ arrangement is especially stable.
What is chromium used for?
Chromium is used in stainless steel, chrome plating, pigments, refractory materials and oxidizing reagents.
Why does stainless steel need chromium?
Chromium forms a thin Cr₂O₃ passive layer that protects stainless steel from corrosion.
Is chromium(VI) dangerous?
Yes. Hexavalent chromium compounds are toxic and carcinogenic, unlike many less hazardous chromium(III) compounds.