Chromium (Cr)
Chromium (Cr) is element 24, a transition metal. Atomic mass 51.9961, configuration [Ar] 3d⁵ 4s¹. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 24 |
|---|---|
| Symbol | Cr |
| Standard atomic weight | 51.9961(6) |
| Category | Transition Metal |
| Group | 6 |
| Period | 4 |
| State at room temperature | Solid |
| Electron configuration | [Ar] 3d⁵ 4s¹ |
| Valence electrons | 1 (Variable) |
| Common oxidation states | +3, +6 |
| Common ions | No common ions |
| Electronegativity (Pauling) | 1.66 |
| First ionization energy | 653 kJ/mol |
| Electron affinity | 64.26 kJ/mol |
| Atomic radius | 166 pm |
| Density | 7.15 g/cm³ |
| Melting point | 1907°C |
| Boiling point | 2671°C |
| Specific heat | 0.449 J/(g·°C) |
Natural isotopes
- Cr-50: Stable
- Cr-52: Stable
- Cr-53: Stable
- Cr-54: Stable
Common uses
- Stainless steel (minimum 10.5%)
- Chrome plating
- Pigments
Where it matters
- Corrosion protection (Stainless steel passivation)
- Environmental Toxicology (Hexavalent chromium)
Hazards
- Cr(VI) is carcinogenic and highly toxic
- Cr(III) essentiality debated in modern literature
History
| Discovered | 1797 |
|---|---|
| Discovered by | Louis-Nicolas Vauquelin |
| Name | From Greek chroma (color) |