Atomic number 24
Chromium
Transition metal
In the real world
Quick facts
- Atomic mass
- 51.996
- Group
- 6
- Period
- 4
- State (STP)
- solid
- Electronegativity
- 1.66
- Common ox. states
- +2, +3, +6
Properties
Electron configuration
[Ar] 3d⁵ 4s¹
- Ionization energy
- 652.9 kJ/mol
- Electron affinity
- 64.3 kJ/mol
- Melting point
- 2180.00 K (1906.8 °C)
- Boiling point
- 2944.00 K (2670.8 °C)
How dangerous is it?
1/5 · Low risk
The shiny chrome on car bumpers is harmless. But one particular form, called chromium-6, is a serious lung carcinogen.
- ToxicBuilds up over time
Chromium-6 compounds damage DNA and cause lung cancer when their dust or mist is breathed. (only chromium-6; the metal and chromium-3 are low-risk)
Chromium-6 work uses sealed ventilation and respiratory protection; the metal itself needs none.
How it bonds
Chromium is one of the textbook electron-config exceptions: 3d⁵ 4s¹ (half-filled d) is more stable than the expected 3d⁴ 4s². Common oxidation states are +3 (Cr₂O₃, the green oxide) and +6 (Cr₂O₇²⁻, the orange dichromate ion - toxic and carcinogenic).
