Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
In the short form, [Ar] stands for the 18 electrons of argon, the noble gas before calcium. Only the electrons after it are written out.
Orbital diagram
3s↑↓
3p↑↓↑↓↑↓
4s↑↓
Outer subshells only. Each box is an orbital; electrons fill singly first (Hund's rule), then pair up with opposite spins.
What the configuration tells you
Calcium fills 4s completely. The next element, scandium, starts filling 3d.
Configuration of calcium ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| Ca²⁺ | [Ar] | 0 | 0.00 |
Moment is the spin-only magnetic moment μ = √(n(n + 2)) Bohr magnetons, where n is the number of unpaired electrons.
Nearby elements
| Z | Element | Configuration |
|---|---|---|
| 17 | Chlorine | [Ne] 3s² 3p⁵ |
| 18 | Argon | [Ne] 3s² 3p⁶ |
| 19 | Potassium | [Ar] 4s¹ |
| 21 | Scandium | [Ar] 3d¹ 4s² |
| 22 | Titanium | [Ar] 3d² 4s² |
| 23 | Vanadium | [Ar] 3d³ 4s² |
Questions students ask
What is the electronic configuration of calcium?
[Ar] 4s², or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². Calcium has atomic number 20.
How many electrons are in each shell of calcium?
2, 8, 8, 2 (K, L, M, N… shells in order).
How many unpaired electrons does calcium have?
0 in the ground state, so calcium atoms are diamagnetic.
What is the electronic configuration of Ca²⁺?
[Ar], with 0 unpaired electrons.