Cesium (Cs)
Cesium is element 55, a alkali metal in period 6, group 1 of the periodic table. At room temperature it is a solid.
Electron configuration [Xe] 6s1
Electrons per shell 2, 8, 18, 18, 8, 1
Cesium data
| Atomic number | 55 |
|---|---|
| Symbol | Cs |
| Atomic mass | 132.905 u |
| Category | Alkali metal |
| Group | 1 |
| Period | 6 |
| Block | s |
| State at 25 °C | solid |
| Melting point | 302 K (28.9 °C) |
| Boiling point | 944 K (670.9 °C) |
| Density | 1.879 g/cm³ |
| Electronegativity (Pauling) | 0.79 |
| Atomic radius | 225 pm |
| 1st ionization energy | 376 kJ/mol |
| Electron affinity | -46 kJ/mol |
| Oxidation states | +1 |
| Common ion charge | + |
| Discovered | 1860 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through cesium’s configuration and its ions →
Where cesium sits
Cesium belongs to the alkali metals. Its Pauling electronegativity of 0.79 is among the lowest on the table, so it gives up electrons readily; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Cesium FAQ
What is the electron configuration of cesium?
Cesium (Z = 55) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1. In noble-gas shorthand that is [Xe] 6s1.
How many valence electrons does cesium have?
1 (outer shell (n = 6)).
What is the atomic mass of cesium?
The standard atomic weight of cesium is 132.905 u, so one mole weighs 132.905 g.
Is cesium a metal?
Yes. Cesium is a alkali metal.
What is the charge of a cesium ion?
Cesium most commonly forms Cs+.