Cesium

Chaitra 26/06/2026 19:58:08 Updated 26/06/2026 19:58:08

Property	Value
Atomic Number	55
Element	Cesium
Symbol	Cs
Atomic Mass	132.905 u
Number of Neutrons	78 (most common isotope, Cesium-133)
Number of Protons	55
Number of Electrons	55
Period	6
Group	1
Phase	Solid (melts near room temperature)
Radioactive	No
Natural	Yes
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Alkali Metal
Atomic Radius	298 pm
Electronegativity	0.79 (Pauling scale)
First Ionization Energy	3.894 eV
Density	1.93 g/cm³
Melting Point	28.44 °C
Boiling Point	671 °C
Number of Isotopes	1 stable (Cesium-133)
Discoverer	Robert Bunsen, Gustav Kirchhoff
Year	1860
Specific Heat	0.242 J/g·K
Number of Shells	6
Number of Valence Electrons	1