Cesium (Cs)
Cesium (Cs) is element 55, an alkali metal. Atomic mass 132.90545196, configuration [Xe] 6s¹. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 55 |
|---|---|
| Symbol | Cs |
| Standard atomic weight | 132.90545196(6) |
| Category | Alkali Metal |
| Group | 1 |
| Period | 6 |
| State at room temperature | Solid |
| Electron configuration | [Xe] 6s¹ |
| Valence electrons | 1 |
| Common oxidation states | +1 |
| Common ions | No common ions |
| Electronegativity (Pauling) | 0.79 |
| First ionization energy | 376 kJ/mol |
| Electron affinity | 45.51 kJ/mol |
| Atomic radius | 298 pm |
| Density | 1.873 g/cm³ |
| Melting point | 28.51°C |
| Boiling point | 671°C |
| Specific heat | 0.242 J/(g·°C) |
Natural isotopes
- Cs-133: Stable
Common uses
- Atomic clocks (GPS standard)
- Drilling fluids (Cesium formate)
- Photoelectric cells
Where it matters
- Global Timekeeping (Definition of the Second based on Cs-133)
Hazards
- Reacts explosively with cold water
History
| Discovered | 1860 |
|---|---|
| Discovered by | Robert Bunsen & Gustav Kirchhoff |
| Name | From Latin caesius (sky blue spectrum line) |