Page 42 - Curriculum Visions Dynamic Book

Argon, krypton, xenon and radon
Argon is the third of the noble gases in the periodic table. It is much more abundant than the other noble gases, making up the great majority of the noble gases in the atmosphere. It is 0.94% of the air by volume (the total volume of all the noble gases is less than 1%).
Like all the noble gases, argon is obtained for industrial use by cooling air down to very low temperatures, and then collecting the element when it changes from gas to liquid at -185.7°C.
The fourth, fifth and sixth members of the noble gases are krypton, xenon and radon. They have higher atomic numbers than the other members of the group, more compounds associated with them, and radioactive forms (called isotopes). Radon is composed entirely of radioactive isotopes. Some of the radioactive isotopes of krypton are made as part of the nuclear processes that occur during electric power generation. Radon is colourless,
but xenon gives blue, and krypton violet, light when excited by an electrical current.
Xenon
Xenon, symbol Xe, which is a Greek word meaning “a stranger”, is the fifth member of the group of noble gases in the Periodic Table. It is the rarest of all the gases, being present in the atmosphere at a concentration of only one part in twenty million by volume.
It produces a bright blue glow when used as the gas in a discharge tube. The light emitted from high-intensity bulbs is a bluish-white colour and is widely used as the source of light for lighthouses and for stroboscopes used at rock concerts.
 The intense light source from a lighthouse is provided by a discharge tube filled with xenon.
Uses for argon
Argon is used together with nitrogen in incandescent tubes and also in fluorescent tubes.
It is also used in factories making silicon wafers, providing an inert environment in which the silicon crystals can grow as they are slowly extracted from the molten silicon.
 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 efficiency of the light.
Argon and nitrogen are inert gases and so do not change in the intense heat of the filament. The presence of gas molecules also means that the atoms leaving the filament are more likely to encounter the gas and bounce back on the filament than they are to reach the glass of the bulb. This prolongs the life
of the bulb and stops it from blackening.
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