Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹
In the short form, [Kr] stands for the 36 electrons of krypton, the noble gas before rubidium. 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
Rubidium is in group 1, period 5, in the s-block. It has 1 unpaired electron in the ground state, so the atom is paramagnetic.
Configuration of rubidium ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| Rb⁺ | [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 |
|---|---|---|
| 34 | Selenium | [Ar] 3d¹⁰ 4s² 4p⁴ |
| 35 | Bromine | [Ar] 3d¹⁰ 4s² 4p⁵ |
| 36 | Krypton | [Ar] 3d¹⁰ 4s² 4p⁶ |
| 38 | Strontium | [Kr] 5s² |
| 39 | Yttrium | [Kr] 4d¹ 5s² |
| 40 | Zirconium | [Kr] 4d² 5s² |
Questions students ask
What is the electronic configuration of rubidium?
[Kr] 5s¹, or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹. Rubidium has atomic number 37.
How many electrons are in each shell of rubidium?
2, 8, 18, 8, 1 (K, L, M, N… shells in order).
How many unpaired electrons does rubidium have?
1 in the ground state, so rubidium atoms are paramagnetic.
What is the electronic configuration of Rb⁺?
[Kr], with 0 unpaired electrons.