cesium133atomin
Cesium-133 is the only stable isotope of the alkali metal cesium (atomic number 55). It has 55 protons and 78 neutrons, giving a mass number of 133. In nature, cesium is essentially Cs-133. The nucleus has a spin of 7/2, and the ground-state electronic configuration is [ Xe ] 6s1. The first ionization energy is about 375.7 kJ/mol.
Cesium-133 is best known for its role in timekeeping. The hyperfine transition between the two ground-state
Chemistry and physical properties: Cesium is a soft, highly reactive alkali metal. It has a melting point
Occurrence and history: Cesium was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff from mineral water.