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Argon (Ar)

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).

Argon in the periodic table

Atomic number18
Element categoryNoble Gas

Physical properties

Phase at STPGas
Density1.784 g/cm3
Atomic weight39.9481 u
Melting point83.81 K
-189.34 °C
-308.812 °F
Boiling point87.302 K
-185.848 °C
-302.5264 °F

Atomic properties

Electronegativity (Pauling Scale)
Electron affinity-96 kJ/mol
Oxidation states0
Ionization energies
11520.6 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

Elektronkonfiguration (shorthand)[Ne] 3s2 3p6
Electron configuration1s2 2s2 2p6 3s2 3p6
Electrons per shell2, 8, 8


Discovered byLord Rayleigh
William Ramsay
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