Atomic number 55
Cesium
Alkali metal
Quick facts
- Atomic mass
- 132.91
- Group
- 1
- Period
- 6
- State (STP)
- solid
- Electronegativity
- 0.79
- Common ox. states
- +1
Properties
Electron configuration
[Xe] 6s¹
- Ionization energy
- 375.7 kJ/mol
- Electron affinity
- 45.5 kJ/mol
- Melting point
- 301.70 K (28.6 °C)
- Boiling point
- 944.00 K (670.9 °C)
How it bonds
Cesium has the lowest ionization energy of any stable element — its 6s electron is so far from the nucleus that almost anything will pull it off. Cs⁺ is the only common form. Atomic clocks count cesium-133 transitions to define the second.