55
Cs
132.91
Cesium
Element 55 · 132.91 u · s-block
alkali metal
The most electropositive stable element. Melts near body temperature. Used in atomic clocks that define the second.
Phase (STP)
Solid
Melting Point
28.44 °C
Boiling Point
671 °C
Density
1.873 g/cm³
Electronegativity
0.79
Atomic Radius
260 pm
Ionization Energy
376 kJ/mol
Electron Affinity
46 kJ/mol
Discovered
1860 · Robert Bunsen
Electron Configuration
[Xe] 6s1
Electron Orbitals
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