55 Cs
Alkali metal
Cesium
Defines the SI second.
Properties of Cesium
- Atomic number (Z)
- 55
- Symbol
- Cs
- Atomic mass
- 132.91 g/mol
- Category
- Alkali metal
- Group
- 1
- Period
- 6
- Electron configuration
- [Xe] 6s¹
- Electronegativity (Pauling)
- 0.79
- Atomic radius
- 298 pm
- First ionization energy
- 376 kJ/mol
- Melting point
- 301.59 K (28.4 °C)
- Boiling point
- 944 K (670.9 °C)
- Density
- 1.873 g/cm³
- Phase at 25 °C
- Solid
- Discovered
- Discovered in 1860