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Compare Helium vs Argon

Comparing Helium (He) and Argon (Ar). Atomic numbers 2 and 18 with atomic masses 4.003 u and 39.792 u, classified as noble gas and noble gas. 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
He
Helium
#2
Ar
Argon
#18

Periodic properties of the elements

HeliumArgon
SymbolHeAr
Atomic number218
Group1818
Period13
Blocksp
Element categoryNoble GasNoble Gas

Physical properties

HeliumArgon
Phase at STPGasGas
Density0.1786 g/cm31.784 g/cm3
Atomic weight4.0026 u39.792 u
Melting point0.95 K
-272.2 °C
-457.96 °F		83.81 K
-189.34 °C
-308.812 °F
Boiling point4.222 K
-268.928 °C
-452.0704 °F		87.302 K
-185.848 °C
-302.5264 °F

Atomic properties

HeliumArgon
Electronegativity (Pauling Scale)00
Electron affinity-48 kJ/mol-96 kJ/mol
Oxidation states00
Ionization energies
  1. 2372.3 kJ/mol
  2. 5250.5 kJ/mol
  1. 1520.6 kJ/mol
  2. 2665.8 kJ/mol
  3. 3931 kJ/mol
  4. 5771 kJ/mol
  5. 7238 kJ/mol
  6. 8781 kJ/mol
  7. 11995 kJ/mol
  8. 13842 kJ/mol
  9. 40760 kJ/mol
  10. 46186 kJ/mol
  11. 52002 kJ/mol
  12. 59653 kJ/mol
  13. 66199 kJ/mol
  14. 72918 kJ/mol
  15. 82473 kJ/mol
  16. 88576 kJ/mol
  17. 397605 kJ/mol
  18. 427066 kJ/mol

Electron configuration

HeliumArgon
Shorthand configuration1s2 [Ne] 3s2 3p6
Full configuration1s2 1s2 2s2 2p6 3s2 3p6
Electrons per shell22, 8, 8

History

HeliumArgon
DiscoveryPierre Janssen, Norman Lockyer (1868)Lord Rayleigh, William Ramsay (1894)
First isolationWilliam Ramsay, Per Teodor Cleve, Abraham Langlet (1895)Lord Rayleigh, William Ramsay (1894)
Named byEdward Frankland, Norman Lockyer (1868)
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