Cesium
Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
54 is the [Xe] core total across five shells.
At a glance
- Atomic number
- 55
- Atomic mass
- 132.905452 u
- Phase
- Solid
- Density
- 1.93 g/cm³
- Melting point
- 301.7 K
- Boiling point
- 944 K
- First ionization energy
- 375.7 kJ/mol
- Electronegativity
- 0.79
- Electron affinity
- 45.505 kJ/mol
- Molar heat capacity
- 32.21 J/(mol·K)
- Period
- 6
- Appearance
- silvery gold
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.