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Argon (Ar)

Argon is a chemical element of the periodic table with chemical symbol Ar and atomic number 18 with an atomic weight of 39.792 u and is classed as noble gas and is part of group 18 (noble gases). Argon is gas at room temperature.

Argon in the periodic table

Atomic number18
Group18 (Noble gases)
ClassificationNoble Gas
AppearanceColorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
Color Colorless
Number of protons18 p+
Number of neutrons22 n0
Number of electrons18 e-
From Wikipedia, the free encyclopediaArgon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most common gas in the Earth's atmosphere, at 0.934% (9,340 ppmv), making it over twice as abundant as the next most common atmospheric gas, water vapor (which averages about 4000 ppmv, but varies greatly), and 23 times as abundant as the next most common non-condensing atmospheric gas, carbon dioxide (400 ppmv), and more than 500 times as abundant as the next most common noble gas, neon (18 ppmv).

Physical properties

Phase at STPGas
Density1.784 g/cm3
Atomic weight39.792 u

Thermal properties

Melting point83.81 K
-189.34 °C
-308.812 °F
Boiling point87.302 K
-185.848 °C
-302.5264 °F
Heat of vaporization6.506 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)-
Electron affinity-96 kJ/mol
Oxidation states0
Ionization energies
  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 for argon

Electron configuration
Shorthand configuration
[Ne] 3s2 3p6
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6
Electron configuration chart
Electrons per shell2, 8, 8
Valence electrons 8
Valency electrons 0
Bohr model
ArgonElectron shell for Argon, created by Injosoft ABAr
Figure: Shell diagram of Argon (Ar) atom.
Orbital Diagram

The history of Argon

Discovery and first isolationLord Rayleigh, William Ramsay (1894)
Discovery of argon
Argon (Greek ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive") is named in reference to its chemical inactivity. This chemical property of this first noble gas to be discovered impressed the namers. An unreactive gas was suspected to be a component of air by Henry Cavendish in 1785. Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air. They first accomplished this by replicating an experiment of Henry Cavendish's.


List of unique identifiers for Argon in various chemical registry databases
CAS Number7440-37-1
ChemSpider ID22407
EC number231-147-0
PubChem CID Number23968