Full configuration
1s² 2s² 2p⁶ 3s² 3p⁵
In the short form, [Ne] stands for the 10 electrons of neon, the noble gas before chlorine. Only the electrons after it are written out.
Orbital diagram
2p↑↓↑↓↑↓
3s↑↓
3p↑↓↑↓↑
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
Chlorine is one electron short of argon's configuration, so it gains one to become Cl⁻.
Configuration of chlorine ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| Cl⁻ | [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 |
|---|---|---|
| 14 | Silicon | [Ne] 3s² 3p² |
| 15 | Phosphorus | [Ne] 3s² 3p³ |
| 16 | Sulphur | [Ne] 3s² 3p⁴ |
| 18 | Argon | [Ne] 3s² 3p⁶ |
| 19 | Potassium | [Ar] 4s¹ |
| 20 | Calcium | [Ar] 4s² |
Questions students ask
What is the electronic configuration of chlorine?
[Ne] 3s² 3p⁵, or in full, 1s² 2s² 2p⁶ 3s² 3p⁵. Chlorine has atomic number 17.
How many electrons are in each shell of chlorine?
2, 8, 7 (K, L, M, N… shells in order).
How many unpaired electrons does chlorine have?
1 in the ground state, so chlorine atoms are paramagnetic.
What is the electronic configuration of Cl⁻?
[Ar], with 0 unpaired electrons.