Periodic Table of Elements




Caesium was discovered by German chemists, Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, in 1860 by the newly developed method of flame spectroscopy.

Name: Caesium
Symbol: Cs
Atomic number: 55
Atomic weight: 132.91
State: solid
Group, period, block: 1, 6, s
Color: silvery gold
Classification: alkali metal
Electron configuration: 6s1

Physical properties

Density: 1.93 g/cm-3
Melting point: 301.59 K, 28.44 C, 83.19 F
Boiling point: 944 K, 671 C, 1240 F

Atomic properties

Oxidation states: 1
Electronegativity: 0.79 (Pauling scale)
Ionization energies: 1st: 375.7 kJmol-1
Covalent radius: 24411 pm
Van der Waals radius: 343 pm
  • Cs
  • Electron Configuration


There is one naturally occurring isotope of caesium exists, 133Cs.