Krypton
Krypton is an element denoted by the atomic symbol Kr. Its atomic number is 36 and its atomic weight is 83.80. In its natural form it is a colorless, odorless, tasteless gas. It is found in the atmosphere in small quantities (about one part per million), and trace amounts occur in minerals, mineral springs, and meteorites. Commercially, krypton is produced by separation from liquefied air. The gas has some 26 isotopes, of which about 20 are radioactive. Nuclear reactors produce radioactive krypton isotopes as by-products of power generation. These isotopes can also be created by nuclear particle accelerators.
When the first Superman comic book appeared in 1938, the word "krypton" entered the American vocabulary as the planet where the hero was born and "kryptonite" as the mysterious substance that could rob him of his powers. While the planet and the mineral are fiction, their namesake exists as an inert gas. The story of krypton's discovery began when Sir William Ramsay responded to a puzzle posed in a scientific journal by John William Strutt ( Lord Rayleigh), a fellow chemist. Why was nitrogen extracted from the air heavier than nitrogen obtained from chemical compounds? As it turned out, atmospheric nitrogen contained a small amount of unidentified gas. When analyzed, this mysterious gas proved to be an entirely new element, which Ramsay and Rayleigh named argon, after the Greek word for "lazy," because it would not react with other elements to form compounds. The new gas's position on the periodic table of elements implied that argon was one of a family of gases--other new elements with a similar nature--so Ramsay set out to find argon's relatives.
In 1898, after identifying helium, Ramsay and another English chemist, Morris Travers (1872-1961), isolated certain fractions of argon that turned out to contain three more new gases, one of which was krypton. They named the new element after the Greek word for "hidden" because it had been so difficult for them to isolate. Since then, much more has been learned about krypton and the other inert gases-- neon, xenon, and radon, in addition to argon and helium.
Until 1962, krypton and its sister elements were thought to be totally inert, or nonreactive. Then British chemist Neil Bartlett created a stable compound containing xenon, and scientists soon formed compounds with krypton as well. However, no one has been able to prepare a krypton compound that is stable at room temperature, and the only well-characterized compound is krypton difluoride. Certain unstable complexes of krypton and fluorine, which act as powerful fluorinating agents, have been used to create other exotic new chemicals, such as a synthesis of gold and fluorine.
For more than 20 years (from 1960 to 1983), krypton's light waves enjoyed the status of serving as the international standard for the metric unit of length, the meter. This concept had been suggested by French scientist Jacques Babinet (1794-1872) in the 1820s and again by German-American physicist Albert Abraham Michelson in the 1890s, just before krypton's discovery. The light waves emitted by krypton gas include an orange-red component whose wavelength is unusually sharp and well-defined. Beginning in 1960 the meter was defined as an exact multiple of that wavelength (1,650,763.73 times). Eventually, however, with the advent of computer technology, the krypton wavelength measurement was displaced.
But krypton gas has many other valuable applications. For example, it is used to fill electric arc lamps that can pierce through fog for more than 1000 feet (305 m). These brilliant flashing lights, strung along airport runways, guide pilots at night. The extremely brief flash (17 microseconds) avoids blinding the pilot, even though the lights flash on some 40 times per minute. Another type of krypton light uses no electrical energy. Filled with one of krypton's radioactive isotopes, the light operates fluorescently, with the radiation activating the lamp's phosphor coating. Illumination from this light can last for several years. Krypton and krypton-argon mixtures are also used to fill ordinary fluorescent lamps and incandescent filament lights. Although krypton gas costs more than argon, it can provide the same brightness over a longer period of time or, alternatively, it can give a brighter, more efficient light with a slightly reduced life. Slide and movie projectors often use these brighter, krypton-filled lights. Krypton is also employed in gas lasers. Other uses for krypton have been suggested however, its use is limited as a result of its high cost.
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