55

Cs

Caesium
132.9054519 (2)
 Historical Information

Caesium (cesium in USA) was discovered spectroscopically by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff in 1860 in samples of mineral water from Durkheim. Their identification was based upon two bright blue lines in the spectrum. The name caesium (from the Latin "caesius" - heavenly blue) was coined for its bright blue spectroscopic lines.

Basic Information Shells
  • Name:Caesium
  • Symbol: Cs
  • Atomic number: 55
  • Atomic weight:132.9054519 (2)
  • Standard state: a solid at 298 K (but melts only slightly above this temperature)
  • Group in periodic table: 1
  • Group name:Alkali metal
  • Period in periodic table: 6
  • Block in periodic table: s-block
  • Classification: Metallic
 Cesium
Uses Trivia
  • used in atomic clocks
  • IR lamps
  • used in photoelectric cells and vacuum tubes

The metal is characterised by a spectrum containing two bright lines in the blue (accounting for its name). It is silvery gold, soft, and ductile. It is the most electropositive and most alkaline element.