Periodic table › Chromium
1. Identity and classification
Lustrous, hard, high-density silvery or metallic solid with high tensile strength
- Name and symbol
- Chromium (Chromium) · Cr
- Atomic number
- 24
- Relative atomic weight / mass number
- 51.996 ± 0.001
- Group · period · block
- 6 · 4 · d
- Category
- Transition Metal
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-47-3
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 24 · 24
- Neutrons in reference isotope
- 28 (52Cr)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹- Abbreviated configuration
[Ar]3d⁵ 4s¹- Electrons per shell
- 2, 8, 13, 1
- Listed oxidation states
- +6, +3, +2
- Electronegativity
- 1.66 (Pauling)
- First ionization energy
- 652.916 kJ/mol · 6.767 eV
- Electron affinity
- 64.259 kJ/mol
- Covalent radius
- 139 pm
- van der Waals radius
- 189 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 7.15 g/cm³
- Melting point
- 2180 K · 1906.85 °C · 3464.33 °F
- Boiling point
- 2944 K · 2670.85 °C · 4839.53 °F
- Crystal structure
- BCC
- Specific heat
- 0.449 J/(g·K)
- Thermal conductivity
- 93.9 W/(m·K)
- Enthalpy of fusion
- 21 kJ/mol
- Enthalpy of vaporization
- 339.5 kJ/mol
- Magnetic ordering
- Antiferromagnetic
- Mohs hardness
- 8.5
- Speed of sound
- 5940 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The listed electron configuration and oxidation states describe atomic structure; compound properties depend on bonding and composition.
Selected compounds: CrO / Cr₂O₃ (Oxide) · CrClₙ (Chloride) · CrFₙ (Fluoride)
Reaction reference
Oxidation behavior depends on temperature, surface passivation and the chemical environment.
Direct reaction with water is element- and condition-dependent.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 50Cr | Radioactive | 4.345% | GT 1.3E+18 Y |
| 52Cr | Stable | 83.789% | Stable |
| 53Cr | Stable | 9.501% | Stable |
| 54Cr | Stable | 2.365% | Stable |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1797 CE
- Scientists associated with discovery
- Louis Nicolas Vauquelin
- Location
- France (Paris)
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Chromite (FeCr₂O₄)
Named from scientific/historical roots associated with Chromium (Cr), discovered or characterized by Louis Nicolas Vauquelin.
7. Applications
Stainless steel corrosion resistance (≥10.5% Cr), decorative chrome plating, nichrome heating elements, ruby & emerald gemstone coloration
Detailed applications by field
- everyday
- Stainless steel corrosion resistance (≥10.5% Cr), decorative chrome plating, nichrome heating elements, ruby & emerald gemstone coloration
- industry
- Used in transition metal processing, specialized alloys, and chemical manufacturing (Stainless steel corrosion resistance (≥10.5% Cr), decorative chrome plating, nichrome heating elements, ruby & emerald gemstone coloration).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Chromium's electronic structure ([Ar] 3d⁵ 4s¹) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Chromium.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Chromium.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 4 d-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as trace element in human and biological systems.