Chromium (Cr)

Chromium is a transition metal with atomic number 24, in period 4 and group 6 of the periodic table. Its atomic mass is 51.9961 u and its electron configuration is [Ar] 3d⁵ 4s¹. Solid at 25 °C.

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Key facts

Atomic number	24
Atomic mass	51.9961 u
Category	Transition Metal
Period	4
Group	6
Block	d
Electron configuration	[Ar] 3d⁵ 4s¹
Electrons per shell	2, 8, 13, 1
Electronegativity (Pauling)	1.66
Oxidation states	−4, −2, −1, +1, +2, +3, +4, +5, +6common in bold
State at 25 °C	Solid
Melting point	2180 K1906.85 °C
Boiling point	2944 K2670.85 °C
Density	7.19 g/cm³

Atomic properties

First ionization energy	6.767 eV
Electron affinity	64.3 kJ/mol
Atomic radius	130 pm
Covalent radius	139 pm
Van der Waals radius	189 pm
Common ions	Cr³⁺, Cr²⁺
Protons, neutrons, electrons	24, 28, 24

Physical and thermal properties

Molar volume	7.23 cm³/mol
Heat of fusion	20.5 kJ/mol
Heat of vaporization	339 kJ/mol
Specific heat	448 J/(kg·K)
Thermal conductivity	94 W/(m·K)
Thermal expansion	4.9 × 10⁻⁶ K⁻¹
Mohs hardness	8.5
Young’s modulus	279 GPa
Crystal structure	Body-centered cubic
Magnetic type	Antiferromagnetic

Identification and history

CAS number	7440-47-3
Latin name	Chromium
Discovered by	Louis Nicolas Vauquelin · 1797
Named by	---

Natural isotopes

Isotope	Mass (u)	Abundance
⁵⁰Cr	49.946042	4.345 %
⁵²Cr	51.940505	83.789 %
⁵³Cr	52.940646	9.501 %
⁵⁴Cr	53.938877	2.365 %

Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.

A dash (---) means there is no reliable published measurement. The app never makes one up.

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