Chromium (Cr)
Transition metal
Chromium puts the shine in “chrome” — a hard, brilliantly polishable metal that refuses to tarnish. Mixed into steel it creates stainless steel; its compounds colour rubies red and emeralds green.
Position on the periodic table
Atomic properties
| Atomic number | 24 |
|---|---|
| Atomic mass | 51.9962 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s1 3d5 |
| Noble gas shorthand | [Ar] 3d5 4s1 |
| Electrons per shell | 2, 8, 13, 1 |
| Valence electrons (outer shell) | 1 |
| Common oxidation states | +3, +6, +2 |
| Electronegativity (Pauling) | 1.66 |
| Covalent radius (approx.) | 139 pm |
| First ionization energy | 652.9 kJ/mol |
| Electron affinity | 65.2 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 7.19 g/cm³ |
| Melting point | 1906.8 °C (2180 K) |
| Boiling point | 2670.8 °C (2944 K) |
| Appearance | silvery metallic |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of chromium
Chromium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s1 3d5, usually shortened to [Ar] 3d5 4s1. Its electrons occupy 4 shells (2, 8, 13, 1), placing it in period 4 of the d-block. Explore it interactively in the electron configuration calculator.
Uses of chromium
- Stainless steel (typically ~18% chromium)
- Chrome plating for shine and corrosion resistance
- Pigments (chrome yellow, chrome green)
- Leather tanning
Biological role: Trace amounts of chromium(III) may help insulin function; chromium(VI) is toxic.
Occurrence: Mined almost entirely as chromite ore.
Common compounds of chromium
Cr2O3
Chromium(III) oxide
K2Cr2O7
Potassium dichromate
History and discovery
Discovered: 1797 — Louis Nicolas Vauquelin. Name origin: From Greek chroma, meaning colour, for its vividly coloured compounds.
Louis-Nicolas Vauquelin discovered chromium in 1797 in the bright-red mineral crocoite from Siberia.
Safety notes
Chromium(VI) compounds are carcinogenic and strictly controlled; metallic chromium and Cr(III) are far less hazardous.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Chromium
1. What is the chemical symbol of Chromium?
2. What is the atomic number of Chromium?
3. Which category does Chromium belong to?
4. What is the state of Chromium at room temperature?
5. Which period of the periodic table is Chromium in?
Chromium FAQs
What is the atomic number of chromium?
Chromium's atomic number is 24 — every chromium atom has 24 protons in its nucleus.
What is the symbol for chromium?
Cr. From Greek chroma, meaning colour, for its vividly coloured compounds.
Is chromium a metal, nonmetal, or metalloid?
Chromium is classified as a transition metal.
What state is chromium at room temperature?
At about 25 °C, chromium is a solid. It melts at 1906.8 °C.
What is chromium used for?
Key uses include: stainless steel (typically ~18% chromium); chrome plating for shine and corrosion resistance; pigments (chrome yellow, chrome green).
Related elements
Keep working with this element
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