Chromium (Cr)
Element 24 · Transition metal · atomic mass 51.996 u · group 6, period 4
Electron shells: 2, 8, 13, 1
Chromium is the metal that makes stainless steel stainless, forming an invisible self-repairing oxide skin. Its compounds are intensely coloured, which is how it got its name.
Rubies are red and emeralds green for the same reason: traces of chromium.
- Atomic number
- 24
- Atomic mass
- 51.996 u
- Electron configuration
- [Ar] 3d⁵ 4s¹
- Group · period · block
- 6 · 4 · d
- Oxidation states
- +2, +3, +6
- Electronegativity
- 1.66 (Pauling)
- Melting point
- 1,907 °C
- Boiling point
- 2,671 °C
- Density
- 7.15 g/cm³
- State at 20 °C
- Solid
- Appearance
- Lustrous, hard silvery metal
- Discovered
- Louis-Nicolas Vauquelin, 1797
24 protons, and 24 electrons when neutral
IUPAC standard atomic weight
Chromium group
What Chromium is used for
- Stainless steel
- Decorative and hard chrome plating
- Leather tanning
- Pigments and refractory bricks
Atomic structure of Chromium
A neutral chromium atom has 24 protons and 24 electrons. Its most common isotope carries about 28 neutrons, which is where the mass number 52 comes from. Change the neutron count and you have a different isotope of chromium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 13, 1. In orbital notation that is [Ar] 3d⁵ 4s¹. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Chromium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Chromium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
- Directly below: Molybdenum — same group, one shell larger.
- One proton lighter: Vanadium.
- One proton heavier: Manganese.
Discovery and naming
Chromium was discovered by Louis-Nicolas Vauquelin in 1797. Its name comes from Greek chroma, "colour", which is also why its symbol (Cr) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Chromium?
The standard atomic weight of Chromium is 51.996 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Chromium have?
Chromium has 24 protons, because the atomic number is the proton count and that is what makes an atom Chromium at all. A neutral Chromium atom has the same number of electrons, 24. The neutron count varies by isotope; the most common one has about 28, since 52 − 24 = 28.
What is the electron configuration of Chromium?
The electron configuration of Chromium is [Ar] 3d⁵ 4s¹. Its electrons are arranged 2, 8, 13, 1 across 4 shells.
Is Chromium a metal?
Yes. Chromium is classified as a transition metal, on the metallic side of the table.
What group and period is Chromium in?
Chromium is in group 6 (the chromium group), period 4, in the d-block. The group is its column and the period is its row.
What is the charge of Chromium?
Chromium most commonly forms a 3+ or 6+ or 2+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Chromium?
Chromium melts at 1,907 °C and boils at 2,671 °C. That puts it in the solids at everyday temperatures.
What is Chromium used for?
Stainless steel, Decorative and hard chrome plating, Leather tanning, Pigments and refractory bricks. Chromium is the metal that makes stainless steel stainless, forming an invisible self-repairing oxide skin.
Who discovered Chromium, and where does its name come from?
Chromium (Cr) was discovered by Louis-Nicolas Vauquelin in 1797. The name comes from Greek chroma, "colour".