Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³
In the short form, [Ar] stands for the 18 electrons of argon, the noble gas before arsenic. Only the electrons after it are written out.
Orbital diagram
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
Arsenic is in group 15, period 4, in the p-block. It has 3 unpaired electrons in the ground state, so the atom is paramagnetic.
Configuration of arsenic ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| As³⁻ | [Kr] | 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 |
|---|---|---|
| 30 | Zinc | [Ar] 3d¹⁰ 4s² |
| 31 | Gallium | [Ar] 3d¹⁰ 4s² 4p¹ |
| 32 | Germanium | [Ar] 3d¹⁰ 4s² 4p² |
| 34 | Selenium | [Ar] 3d¹⁰ 4s² 4p⁴ |
| 35 | Bromine | [Ar] 3d¹⁰ 4s² 4p⁵ |
| 36 | Krypton | [Ar] 3d¹⁰ 4s² 4p⁶ |
Questions students ask
What is the electronic configuration of arsenic?
[Ar] 3d¹⁰ 4s² 4p³, or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³. Arsenic has atomic number 33.
How many electrons are in each shell of arsenic?
2, 8, 18, 5 (K, L, M, N… shells in order).
How many unpaired electrons does arsenic have?
3 in the ground state, so arsenic atoms are paramagnetic.
What is the electronic configuration of As³⁻?
[Kr], with 0 unpaired electrons.