Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹
In the short form, [Ar] stands for the 18 electrons of argon, the noble gas before copper. 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.
Why it's an exception
Copper is an exception. A completely filled 3d¹⁰ is more stable than 3d⁹ 4s², so one 4s electron moves into 3d.
Configuration of copper ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| Cu⁺ | [Ar] 3d¹⁰ | 0 | 0.00 |
| Cu²⁺ | [Ar] 3d⁹ | 1 | 1.73 |
Moment is the spin-only magnetic moment μ = √(n(n + 2)) Bohr magnetons, where n is the number of unpaired electrons. Positive ions lose electrons from the outermost shell first, so transition metals lose their 4s or 5s electrons before d.
Nearby elements
| Z | Element | Configuration |
|---|---|---|
| 26 | Iron | [Ar] 3d⁶ 4s² |
| 27 | Cobalt | [Ar] 3d⁷ 4s² |
| 28 | Nickel | [Ar] 3d⁸ 4s² |
| 30 | Zinc | [Ar] 3d¹⁰ 4s² |
| 31 | Gallium | [Ar] 3d¹⁰ 4s² 4p¹ |
| 32 | Germanium | [Ar] 3d¹⁰ 4s² 4p² |
Questions students ask
What is the electronic configuration of copper?
[Ar] 3d¹⁰ 4s¹, or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹. Copper has atomic number 29.
How many electrons are in each shell of copper?
2, 8, 18, 1 (K, L, M, N… shells in order).
How many unpaired electrons does copper have?
1 in the ground state, so copper atoms are paramagnetic.
What is the electronic configuration of Cu⁺?
[Ar] 3d¹⁰, with 0 unpaired electrons.
Why is copper an exception?
Copper is an exception. A completely filled 3d¹⁰ is more stable than 3d⁹ 4s², so one 4s electron moves into 3d.