Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
In the short form, [Ar] stands for the 18 electrons of argon, the noble gas before potassium. 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
The 19th electron goes into 4s, not 3d, because 4s is lower in energy for potassium (n + l is 4 for 4s and 5 for 3d).
Configuration of potassium ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| K⁺ | [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 |
|---|---|---|
| 16 | Sulphur | [Ne] 3s² 3p⁴ |
| 17 | Chlorine | [Ne] 3s² 3p⁵ |
| 18 | Argon | [Ne] 3s² 3p⁶ |
| 20 | Calcium | [Ar] 4s² |
| 21 | Scandium | [Ar] 3d¹ 4s² |
| 22 | Titanium | [Ar] 3d² 4s² |
Questions students ask
What is the electronic configuration of potassium?
[Ar] 4s¹, or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹. Potassium has atomic number 19.
How many electrons are in each shell of potassium?
2, 8, 8, 1 (K, L, M, N… shells in order).
How many unpaired electrons does potassium have?
1 in the ground state, so potassium atoms are paramagnetic.
What is the electronic configuration of K⁺?
[Ar], with 0 unpaired electrons.