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Compare Potassium vs Calcium

Comparing Potassium (K) and Calcium (Ca). Atomic numbers 19 and 20 with atomic masses 39.098 u and 40.078 u, classified as alkali metal and alkaline earth 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
Ca
Calcium
#20

Periodic properties of the elements

PotassiumCalcium
SymbolKCa
Atomic number1920
Group12
Period44
Blocksd
Element categoryAlkali MetalAlkaline Earth Metal

Physical properties

PotassiumCalcium
Phase at STPSolidSolid
Density0.862 g/cm31.55 g/cm3
Atomic weight39.0983 u40.0784 u
Melting point336.7 K
63.55 °C
146.39 °F		1115 K
841.85 °C
1547.33 °F
Boiling point1032 K
758.85 °C
1397.93 °F		1757 K
1483.85 °C
2702.93 °F

Atomic properties

PotassiumCalcium
Electronegativity (Pauling Scale)0.821
Electron affinity48.383 kJ/mol2.37 kJ/mol
Oxidation states−1, +1
(a strongly basic oxide)		+1, +2
(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. 589.8 kJ/mol
  2. 1145.4 kJ/mol
  3. 4912.4 kJ/mol
  4. 6491 kJ/mol
  5. 8153 kJ/mol
  6. 10496 kJ/mol
  7. 12270 kJ/mol
  8. 14206 kJ/mol
  9. 18191 kJ/mol
  10. 20385 kJ/mol
  11. 57110 kJ/mol
  12. 63410 kJ/mol
  13. 70110 kJ/mol
  14. 78890 kJ/mol
  15. 86310 kJ/mol
  16. 94000 kJ/mol
  17. 104900 kJ/mol
  18. 111711 kJ/mol
  19. 494850 kJ/mol
  20. 527762 kJ/mol

Electron configuration

PotassiumCalcium
Shorthand configuration[Ar] 4s1 [Ar] 4s2
Full configuration1s2 2s2 2p6 3s2 3p6 4s1 1s2 2s2 2p6 3s2 3p6 4s2
Electrons per shell2, 8, 8, 12, 8, 8, 2

History

PotassiumCalcium
DiscoveryHumphry Davy (1807)Humphry Davy (1808)
First isolationHumphry Davy (1807)Humphry Davy (1808)
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