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Compare Potassium vs Rubidium

Comparing Potassium (K) and Rubidium (Rb). Atomic numbers 19 and 37 with atomic masses 39.098 u and 85.468 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
Rb
Rubidium
#37

Periodic properties of the elements

PotassiumRubidium
SymbolKRb
Atomic number1937
Group11
Period45
Blockss
Element categoryAlkali MetalAlkali Metal

Physical properties

PotassiumRubidium
Phase at STPSolidSolid
Density0.862 g/cm31.532 g/cm3
Atomic weight39.0983 u85.4678 u
Melting point336.7 K
63.55 °C
146.39 °F		312.45 K
39.3 °C
102.74 °F
Boiling point1032 K
758.85 °C
1397.93 °F		961 K
687.85 °C
1270.13 °F

Atomic properties

PotassiumRubidium
Electronegativity (Pauling Scale)0.820.82
Electron affinity48.383 kJ/mol46.884 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. 403 kJ/mol
  2. 2633 kJ/mol
  3. 3860 kJ/mol
  4. 5080 kJ/mol
  5. 6850 kJ/mol
  6. 8140 kJ/mol
  7. 9570 kJ/mol
  8. 13120 kJ/mol
  9. 14500 kJ/mol
  10. 26740 kJ/mol

Electron configuration

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

History

PotassiumRubidium
DiscoveryHumphry Davy (1807)Robert Bunsen, Gustav Kirchhoff (1861)
First isolationHumphry Davy (1807)Robert Bunsen (1863)
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