Cesium, Cs

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft silvery-gold alkali metal with a melting point of 28 °C (83 °F), which makes it one of the metals that are liquid at or near room temperature, along with rubidium (39 °C [102 °F]), francium (27 °C [81 °F]), mercury (−39 °C [−38 °F]), and gallium (30 °C [86 °F]). This element is most notably used in atomic clocks.

The variant spelling cesium is used especially in North American English, but caesium is the spelling used by the IUPAC.

Technical Data
Symbol Cs Density (25°C)/gcm-3 1.9
Atomic number 55 Melting point / °C 28.5
No. of naturally occurring isotopes 1 Boiling point / °C 705
Atomic weight 132.9054 ΔHfus/kJmol-1 2.09
Electronic configuration [Xe] 6s1 ΔHvap/kJmol-1 67
Ionization energy/kJmol-1 375.6 ΔHf(monoatomic gas)/kJmol-1 79
Metal radius/pm 265 Eo(M+(aq)+e- →M(S))/V -2.92
Ionic radius (6-coordinate)/pm 167    
Evaporation Techniques
Temperature (oC) @Vap. Pressure Techniques Remarks
10-8 Torr 10-6 Torr 10-4 Torr Electron Beam Crucible Coil Boat
-16 +22 +30 - Quartz - Stainless Steel  

Evaporation Materials
C5-5000-M solid pieces (sealed in glass)