Ar - Argon


Atomic Number: 18
Atomic Weight: 39.948
Element Type: Noble Gas
Crystal Structure: Cubic Face Centered
Melting Point: -189.35°C = -308.83°F = 83.8 K
Boiling Point: -185.85°C = -302.53°F = 87.3 K
Critical Temp: -122.28°C = -188.104°F = 150.87 K
Atomic Radius: 0.88 Å (Å = Angstrom = 10-10 m)
Covalent Radius: 0.98 Å


(Gr. argos, inactive) Its presence in air was suspected by Cavendish in 1785,discovered by Lord Rayleigh and Sir William Ramsay in 1894.


The gas is prepared by fractionation of liquid air because the atmosphere contains0.94% argon. The atmosphere of Mars contains 1.6% of 40Ar and 5 p.p.m. of 36Ar.

Science Quote

'The mathematician's patterns, like the painter's or the poets, must be beautiful; the ideas, like the colours or the words, must fit together in a harmonious way. Beauty is the first test: there is no permanent place in the world for ugly mathematics.'

Godfrey Hardy

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