Chromium (Cr): electron configuration, atomic mass and facts
Chromium (Cr) is element 24 of the periodic table, a transition metal in period 4, group 6. Its electron configuration is [Ar] 3d5 4s1, with electrons arranged in shells 2, 8, 13, 1, and its standard atomic weight is 51.996 u.
💡 Gives rubies their red colour and chrome its shine.
▶ Watch Chromium’s electrons orbit in the interactive periodic tableChromium at a glance
| Symbol | Cr |
|---|---|
| Atomic number | 24 |
| Atomic mass | 51.996 u |
| Category | Transition metal |
| Group | 6 |
| Period | 4 |
| Block | d-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d5 4s1 |
| Noble-gas shorthand | [Ar] 3d5 4s1 |
| Electrons per shell | 2, 8, 13, 1 |
| Electronegativity (Pauling) | 1.66 |
| State at 20 °C | solid |
Experiments with chromium
Where is Chromium on the periodic table?
Chromium is in period 4, group 6, in the d-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Molybdenum sits directly below it. Elements in the same column of the d-block often have similar chemistry.
How to work out the electron configuration of Chromium
Put 24 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d⁴ (24). Chromium is one of the exceptions to this filling order: experiments show its ground state is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵ rather than 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴, because the neighbouring subshells are so close in energy and a half-filled or completely filled d subshell is extra stable. In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 3d⁵ 4s¹.
How electronegative is Chromium?
Chromium has a Pauling electronegativity of 1.66, ranking 46 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Chromium in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain chromium: Potassium dichromate. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Chromium?
The electron configuration of Chromium (Cr) is 1s2 2s2 2p6 3s2 3p6 3d5 4s1. In noble-gas shorthand it is written [Ar] 3d5 4s1.
How many electrons does Chromium have in each shell?
Chromium has 24 electrons arranged in shells as 2, 8, 13, 1.
What is the atomic mass of Chromium?
The standard atomic weight of Chromium is 51.996 u, so one mole of Chromium atoms has a mass of about 51.996 g.
Is Chromium a metal?
Yes. Chromium is a transition metal.
Explore nearby elements
More transition metals: Scandium, Titanium, Vanadium, Manganese, Iron, Cobalt. See all elements on the periodic table.