Page 22 - Curriculum Visions Dynamic Book

Argon (Ar)
Element 18.An inert (unreactive) gas and the most abundant member in group 0 (the noble gases) in the Periodic Table. It is not known to form any true compounds.
It is colourless, odourless and tasteless.
Argon is heavier than air.When electricity is passed through argon, the argon glows pale red.The fact that the atmosphere of Mars contains argon was discovered because
argon’s characteristic colour could be detected by special telescopes.
Discovery
Argon was isolated from air in 1894 in
Scotland by Lord Rayleigh and Sir William
Ramsay.When they had removed nitrogen, Argon makes up about 1.3% of the oxygen, carbon dioxide and water from atmosphere by weight and 0.94% liquid air, argon was left. by volume.
Biology
Argon is not an active substance in living things.
 A mixture of argon and nitrogen is used in incandescent light
bulbs.When the filament gets hot, it sends out atoms into the bulb.
If the bulb contained a reactive gas, the life of the filament would be reduced, and a thin film of metal atoms would be deposited on the inside of
the bulb, blackening it and reducing the brightness of the light.
Argon and nitrogen are inert gases and so do not react with the
ntensely hot filament. For more on filaments, see tungsten (W).
Key facts...
Name: argon
Symbol: Ar
Atomic number: 18
Atomic weight: 39.94
Position in Periodic Table: group 8 (18) (noble
gases); period 3
State at room temperature: gas
Colour: colourless
Density of gas at 20°C: 1.66 g/l
Melting point: –189.3°C
Boiling point: –185.8°C
Origin of name: from the Greek word argos,
meaning inactive
Shell pattern of electrons: 2–8–8
Technology
Argon is used in light bulbs and in other places where an unreactive gas is needed, for example, in the manufacture of silicon chips, where an oxygen-free environment is essential.Argon is obtained as a by- product of the liquefaction of air.
Geology
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For more on argon, see Volume 1: Hydrogen and the Noble Gases in the Elements set.
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