Element 55
Cesium (Cs)
Cesium (Cs) is element 55 of the periodic table, a alkali metal in period 6, group 1 (s-block) with an atomic mass of 132.91 and is a solid at standard conditions.
At a glance
- Atomic number
- 55
- Symbol
- Cs
- Atomic mass
- 132.91 u
- Category
- Alkali metals
- Period
- 6
- Group
- 1
- Block
- s-block
- Phase at STP
- solid
Electron structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1
- Shorthand configuration
- [Xe] 6s1
- Electrons per shell
- 2, 8, 18, 18, 8, 1
- Oxidation states
- -1, +1
Physical properties
- Melting point
- 301.59 K
- Boiling point
- 944 K
- Density
- 1.873 g/cm3
- Phase
- solid
Atomic properties
- Electronegativity (Pauling)
- 0.79
- Atomic radius
- 298 pm
- Covalent radius
- 244 pm
- Van der Waals radius
- 343 pm
- First ionization energy
- 376 kJ/mol
- Electron affinity
- 46 kJ/mol
Notable isotopes
| Isotope | Mass | Abundance | Stability |
|---|---|---|---|
| Cs-133 | 132.90545 | 100% | Stable |
Common uses
- Atomic clocks
- Drilling fluids
- Photoelectric cells
- Cancer treatment
Discovery
- Year
- 1860
- Discovered by
- Robert Bunsen, Gustav Kirchhoff
- Country
- Germany