Electron Configuration of Rubidium (Rb)
Rubidium (Rb, Z = 37) has the electron configuration [Kr] 5s^1, filling 5 shells with 2, 8, 18, 8, 1 electrons.
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Rubidium: every subshell, one by one
The table below unpacks [Kr] 5s^1 line by line, so you can watch Rubidium's 37 electrons take their seats in order of increasing energy.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Kr] | 0 | 36 |
| 5s | 1 | 37 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Rubidium carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 8 in shell 4, 1 in shell 5. The outermost shell holds 1 electron — the ones that do all the bonding.
How to derive it yourself
Follow the aufbau order (1s → 2s → 2p → 3s → 3p → 4s → 3d → …), pouring 37 electrons into orbitals of capacity 2 (s), 6 (p), 10 (d) and 14 (f) until none remain. Write the filled inner shells as the nearest noble-gas core — for Rubidium that gives [Kr] 5s^1.
Students also ask
How many electron shells does Rubidium have?
Rubidium is in period 5, so its electrons occupy 5 shells, holding 2, 8, 18, 8, 1 electrons respectively.
How many valence electrons does Rubidium have?
Its outermost shell holds 1 electron, so Rubidium has 1 valence electron that take part in bonding.
What is the noble-gas shorthand for Rubidium?
The shorthand form is exactly [Kr] 5s^1.