Element 24 · Transition metal
Chromium (Cr) — Element 24
Greek chroma — color
Chromium (Cr) is a transition metal in Period 4, Group 6 of the periodic table with atomic number 24, standard atomic weight 51.996 u, and ground-state electron configuration [Ar] 3d⁵ 4s¹. At standard temperature and pressure it is classified as a solid with 6 valence electrons and common oxidation states +3, +6, +2.
Stainless steel, chrome plating
What are the atomic properties and physical constants of Chromium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 24
- Standard atomic mass
- 51.996 u
- Chemical family
- Transition metal
- Ground-state configuration
- [Ar] 3d⁵ 4s¹
- Electrons per shell
- 2, 8, 13, 1
- Valence electrons
- 6
- Common ion charges / oxidation states
- +3, +6, +2
- Phase at STP
- Solid
- Pauling electronegativity
- 1.66 Pauling
- First ionization energy
- 653 kJ/mol
- Atomic radius
- 166 pm
- Melting point
- 1,907 °C
- Boiling point
- 2,671 °C
- Discovery year
- 1797
- Table coordinate
- Period 4, Group 6
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Chromium’s shells?
A neutral Chromium atom contains 24 electrons distributed across 4 occupied principal energy shells ([Ar] 3d⁵ 4s¹). The table below compares Chromium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Cr | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 13 e⁻ | 18 e⁻ |
| n = 4 | N | 1 e⁻ | 32 e⁻ |
Frequently Asked Questions about Chromium (Cr)
What is the atomic mass and atomic number of Chromium (Cr)?
Chromium (Cr) has atomic number Z = 24 (24 protons in its nucleus) and an IUPAC standard atomic weight of 51.996 u. It sits in Period 4, Group 6 and is classified as a transition metal.
What is the ground-state electron configuration of Chromium?
The neutral ground-state electron configuration of Chromium (Z = 24) is [Ar] 3d⁵ 4s¹. Across its 4 occupied principal shells (n = 1 to n = 4), the electrons per shell are 2, 8, 13, 1, with 6 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Chromium?
Chromium commonly forms +3, +6, +2 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.66 and its first ionization energy is 653 kJ/mol.
When was Chromium discovered and what is it used for?
Chromium was discovered in 1797 (Greek chroma — color). Stainless steel, chrome plating
How does Chromium compare to neighboring elements?
Other transition metal elements: