Cesium (Cs) properties

Atomic mass, symbol and atomic number

cesium is a naturally occurring element with the element symbol Cs and atomic number 55. In the periodic table it stands with an atomic mass of 132.90 u in the 1st main group. The chemical element discovered by Robert Bunsen in 1861 is not radioactive and is in a solid state of aggregation at room temperature.

Profile: Cesium (English cesium)

Chemical element:cesium
Atomic number:55
Group:Alkali metals group
Block:s block
Series:alkali metals
explorers:Robert Wilhelm Bunsen
Year of discovery:1861
Atomic properties
Atomic mass:132,905 u
Atomic radius:265 pm
Covalent radius:244 pm
Van der Waals radius:343 pm
Electron configuration:Xe 6s1
ionization:375.7 kJ / mol
Physical Properties
Physical state:firmly
Crystal structure:cubic
molar volume:70,94 · 10-6 m3/ mol
Mohs hardness:0,2
Melting point:28 ° C
Boiling point:690 ° C
Heat of fusion:2.09 kJ / mol
Heat of vaporization:66.1 kJ / mol
Thermal conductivity:36 W
Chemical properties

Did you know that ...

  • Robert Bunsen and Gustav Kirchhoff discovered the element as they studied mineral water?
  • out of a total of 39 known isotopes only the isotope 133Cs naturally occurring on Earth?
  • Cesium with a Mohs hardness of 0.2 is the softest of all elements?
  • Due to the reactor accident in Fukushima (Japan), large parts of the city are contaminated with radioactive cesium?
  • elemental cesium is highly flammable and can explode on contact with air?