Cesium
Alkali Metal
Cesium (Cs) is a chemical element with atomic number 55, classified as a alkali metal. At room temperature it is a solid. It was discovered in 1860 by Robert Bunsen, Gustav Kirchhoff.
Properties
- Atomic number
- 55
- Atomic mass
- 132.91 u
- Category
- Alkali Metal
- Group
- 1
- Period
- 6
- Block
- s-block
- Electron configuration
- [Xe] 6s¹
- Phase at STP
- Solid
- Density
- 1.873 g/cm³
- Melting point
- 301.59 K (28.4 °C)
- Boiling point
- 944 K (670.9 °C)
- Electronegativity
- 0.79
- Atomic radius
- 298 pm
- Ionization energy
- 3.894 eV
- Discovery
- 1860 · Robert Bunsen, Gustav Kirchhoff
Common uses
Atomic clocks, photoelectric cells, catalysts, drilling fluids
Did you know?
Melts in warm weather and defines the second in atomic time.
Experiment with the elements
Cesium doesn't form any compounds in our lab yet, but the periodic table sandbox lets you combine dozens of other real elements into real compounds — water, table salt, ammonia and many more — with their true chemical formulas.