Key information
Atomic number: 
18
Atomic weight: 
39.95
Density: 
1400 kg/m³
Boiling point: 
87.36° K
Melting point: 
83.76° K
Heat vapour: 
6.53 kJ/mol
Heat fusion: 
1.18 kJ/mol
Group: 
Noble Gases

Argon constitutes almost 1% of the atmosphere of the earth. Its name is derived from the Greek Argos meaning inert. This lack of reactivity resulted in it being discovered relatively late on: in 1894. The British chemists John Rayleigh and William Ramsay on the basis of Cavendish's experiment were able to determine the presence of argon, a noble gas, in air. As with Cavendish's experiment a bubble of gas was left over after removing oxygen and hydrogen from a sample of air. Using spectroscopy, Ramsay found that the lines of the gas were in new places, identifying it as a new element, which he termed argon.

Electron Shell: 
Amazon Books
Image of The Last Sorcerers: The Path from Alchemy to the Periodic Table
Author: National Academy of Sciences, Richard Morris
Publisher: Henry (Joseph) Press (2003)
Binding: Hardcover, 294 pages