Electron Configuration of Caesium (Cs)
Caesium (Cs, Z = 55) has the electron configuration [Xe] 6s^1, filling 6 shells with 2, 8, 18, 18, 8, 1 electrons.
This is the fast lane: one page, one fact, zero digressions. Read the quick answer, check the table, and if your exam needs the full derivation, the sections below walk through it step by step — in Bangla and English, like every page here. Need the whole picture instead — history, characteristics, uses, exam questions? The full Caesium page is one click away.
Caesium: every subshell, one by one
The table below unpacks [Xe] 6s^1 line by line, so you can watch Caesium's 55 electrons take their seats in order of increasing energy.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Xe] | 0 | 54 |
| 6s | 1 | 55 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Caesium carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 18 in shell 4, 8 in shell 5, 1 in shell 6. 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 55 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 Caesium that gives [Xe] 6s^1.
Students also ask
How many electron shells does Caesium have?
Caesium is in period 6, so its electrons occupy 6 shells, holding 2, 8, 18, 18, 8, 1 electrons respectively.
How many valence electrons does Caesium have?
Its outermost shell holds 1 electron, so Caesium has 1 valence electron that take part in bonding.
What is the noble-gas shorthand for Caesium?
The shorthand form is exactly [Xe] 6s^1.