Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Argon

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Argon, symbol Ar, inert gaseous element that is the third most prevalent gas in the earth's atmosphere. In group 18 (or VIIIa) of the periodic table, argon is one of the noble gases. The atomic number of argon is 18.

Argon was discovered in 1894 by the British scientists Sir William Ramsay and Baron John William Strutt Rayleigh. They were led to this discovery by a discrepancy between the density of supposedly pure nitrogen, prepared from air, and actually pure nitrogen, prepared from ammonium nitrate. Argon is composed of monatomic molecules and is colorless and odorless.It constitutes 0.93 percent of the atmosphere. Argon melts at -189.3° C (-308.2° F) and boils at -185.86° C (-302.55° F). The atomic weight of argon is 39.948.

In recent years chemists have been able to force most of the noble gases to form compounds. Researchers at the University of Helsinki achieved this feat with argon in 2000. They created argon fluorohydride (HArF) by shining ultraviolet light on frozen argon containing a small amount of hydrogen fluoride.

Argon is produced commercially by the fractional distillation of liquid air. It is used in large quantities to fill electric light bulbs. If air is left in incandescent bulbs, the filament burns; if the bulb is evacuated, as was formerly done, the tungsten filament tends to evaporate, blackening the inside of the bulb. To prevent this evaporation, the bulb can be filled with nitrogen, which is the least expensive gas for the purpose, or argon, which is better, as it is a poorer conductor of heat and so cools the filament less.

Argon is also used in one type of neon lamp. Whereas pure neon gives a red light, argon gives a blue light. Argon tubes require a lower voltage than neon tubes, and for this reason small amounts of argon are sometimes mixed with neon. Argon is also used in electric-arc technology, in gas lasers, and in arc welding.