Chromium Electron Configuration
★ Exception to the Aufbau order. Predicted 1s2 2s2 2p6 3s2 3p6 3d4 4s2; measured 1s2 2s2 2p6 3s2 3p6 3d5 4s1.
Orbital diagram
- Valence electrons
- 6
- Unpaired electrons
- 6
- Block
- d-block
- Magnetism (atom)
- paramagnetic
Electrons per shell
| K (n = 1) | 2 |
|---|---|
| L (n = 2) | 8 |
| M (n = 3) | 13 |
| N (n = 4) | 1 |
Chromium ion configurations
| Ion | Electrons | Configuration |
|---|---|---|
| Cr3+ | 21 | [Ar] 3d3 |
| Cr6+ | 18 | [Ne] 3s2 3p6 |
How to write it
Place 24 electrons into subshells in the Aufbau order (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p), filling s with 2, p with 6, d with 10 and f with 14. Chromium sits in period 4, group 6, in the d-block, so its last electron enters a d subshell. Replacing the inner electrons with the previous noble gas gives the shorthand [Ar] 3d5 4s1.
Try chromium and its ions in the calculator, or see the full chromium data sheet.
Chromium electron configuration FAQ
What is the electron configuration of chromium?
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹. Shorthand (noble gas) notation: [Ar] 3d⁵ 4s¹.
What is the noble gas configuration of chromium?
[Ar] 3d⁵ 4s¹. The bracket stands for the Ar core electrons.
Why is chromium’s electron configuration an exception?
The simple filling (Aufbau) order predicts 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s², but the measured ground state is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹. Shifting an electron gives a half-filled or filled subshell, which has extra exchange stability.
How many valence electrons does chromium have?
6 (1 outer s + 5 d electrons; 1 in the outermost shell).
How many unpaired electrons does chromium have?
6 in the ground state, following Hund’s rule. An atom with unpaired electrons is paramagnetic.
What is the electron configuration of Cr3+?
[Ar] 3d³ (21 electrons). Transition metal cations lose their outer s electrons before d electrons.
What is the electron configuration of Cr6+?
[Ne] 3s² 3p⁶ (18 electrons). Transition metal cations lose their outer s electrons before d electrons.