Caesium (Cs)
[Xe] 6s¹. 1 unpaired electron, period 6, group 1, s block.
Element or ion
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
CsCaesium, Z = 55, 132.905 u
[Xe] 6s1
In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹
- Blocks block
- Period6
- Group1
- Valence1
- Unpaired1
- MagneticPara
Last electron 6s
- n6shell
- l0s subshell
- m0orbital
- s+½spin up
Step by step
- Caesium has 55 electrons.
- Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹.
- Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹.
- Replace the xenon core with [Xe]: [Xe] 6s¹.
Caesium (Cs): the numbers
| Atomic number | 55 |
|---|---|
| Atomic mass | 132.905 u |
| Period | 6 |
| Group | 1 |
| Block | s block |
| Valence electrons | 1 |
| Unpaired electrons | 1 |
| Magnetic | paramagnetic |
| Last electron | 6s: n = 6, l = 0, m = 0, s = +1/2 |
Caesium (Cs): quick answers
What is the electronic configuration of caesium?
Caesium has 55 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹, or [Xe] 6s¹ in short.
How many unpaired electrons does caesium have?
Caesium has 1 unpaired electron, so it is paramagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of caesium?
The last electron goes into 6s: n = 6, l = 0, m = 0, s = +1/2. Orbitals fill from m = −l up, spin +½ first.