(From the Greek argos, "inert") A colorless, odorless, tasteless chemical element, the most abundant of the noble gases, constituting nearly 1% of the atmosphere. It is used in incandescent light bulbs, radio tubes, welding, etc.

Symbol: Ar
Atomic number: 18
Atomic weight: 39.948
Density (at 0°C with 101,325 pascals): 1.78 g/L
Melting point: -189°C
Boiling point: -185.9°C
Valence: 0
Ground state electron configuration: [Ne]3s23p6