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Compare Potassium vs Cesium

Comparing Potassium (K) and Cesium (Cs). Atomic numbers 19 and 55 with atomic masses 39.098 u and 132.905 u, classified as alkali metal and alkali metal. Below: a side-by-side comparison of their physical, atomic, electron-configuration and historical properties, including density, melting and boiling points, ionization energies, oxidation states and discovery history.

vs
K
Potassium
#19
Cs
Cesium
#55

Periodic properties of the elements

PotassiumCesium
SymbolKCs
Atomic number1955
Group11
Period46
Blockss
Element categoryAlkali MetalAlkali Metal

Physical properties

PotassiumCesium
Phase at STPSolidSolid
Density0.862 g/cm31.93 g/cm3
Atomic weight39.0983 u132.905 u
Melting point336.7 K
63.55 °C
146.39 °F		301.7 K
28.55 °C
83.39 °F
Boiling point1032 K
758.85 °C
1397.93 °F		944 K
670.85 °C
1239.53 °F

Atomic properties

PotassiumCesium
Electronegativity (Pauling Scale)0.820.79
Electron affinity48.383 kJ/mol45.505 kJ/mol
Oxidation states−1, +1
(a strongly basic oxide)		−1, +1
(a strongly basic oxide)
Ionization energies
  1. 418.8 kJ/mol
  2. 3052 kJ/mol
  3. 4420 kJ/mol
  4. 5877 kJ/mol
  5. 7975 kJ/mol
  6. 9590 kJ/mol
  7. 11343 kJ/mol
  8. 14944 kJ/mol
  9. 16963.7 kJ/mol
  10. 48610 kJ/mol
  11. 54490 kJ/mol
  12. 60730 kJ/mol
  13. 68950 kJ/mol
  14. 75900 kJ/mol
  15. 83080 kJ/mol
  16. 93400 kJ/mol
  17. 99710 kJ/mol
  18. 444880 kJ/mol
  19. 476063 kJ/mol
  1. 375.7 kJ/mol
  2. 2234.3 kJ/mol
  3. 3400 kJ/mol

Electron configuration

PotassiumCesium
Shorthand configuration[Ar] 4s1 [Xe] 6s1
Full configuration1s2 2s2 2p6 3s2 3p6 4s1 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1
Electrons per shell2, 8, 8, 12, 8, 18, 18, 8, 1

History

PotassiumCesium
DiscoveryHumphry Davy (1807)Robert Bunsen, Gustav Kirchhoff (1860)
First isolationHumphry Davy (1807)Carl Setterberg (1882)
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