Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a rare noble gas found in trace amounts in air, used in some lighting, lasers, insulated glazing, scientific instruments, and isotope applications.
What krypton is
Krypton is a noble gas element. At ordinary conditions it is colorless, odorless, nonflammable, and made of individual atoms rather than molecules. It is much rarer in air than argon and neon, which makes it more expensive and more specialized in everyday use.
Why krypton is a noble gas
Krypton belongs to Group 18 of the periodic table. Its outer electron shell is filled, so it reacts only under unusual conditions compared with most elements. This low reactivity makes krypton useful when a stable gas is needed, especially in lighting, sealed spaces, and scientific equipment.
Discovery and name
Krypton was discovered in 1898 by William Ramsay and Morris Travers while studying residues from liquefied air. Its name comes from the Greek word kryptos, or hidden, because the element was hard to find in the small leftover fraction after more abundant gases had been removed.
Where krypton comes from
Krypton is obtained from air by industrial gas separation. Air is liquefied and separated by boiling-point differences, producing major gases such as nitrogen, oxygen, and argon, plus smaller streams of rare gases. Because krypton is present only in trace amounts, recovery depends on large-scale air separation.
Lighting and discharge tubes
Krypton can glow in gas-discharge tubes when electricity excites its atoms. It has been used in some photographic flash lamps, high-intensity lamps, fluorescent lighting mixtures, and specialty signs. The exact color and performance depend on gas pressure, tube design, current, coatings, and mixtures with other gases.
Windows and insulation
Krypton can be used between panes in insulated glass units. It conducts heat less readily than ordinary air and can perform well in narrow gaps, making it useful in some high-performance windows. It is more costly than argon, so window designers weigh performance gains against price.
Lasers and measurement history
Krypton appears in some lasers and scientific instruments. One isotope, krypton-86, was historically important because a spectral line from krypton-86 was used to define the meter from 1960 until 1983. That role ended when the meter was redefined using the speed of light in vacuum.
Isotopes and safety
Natural krypton has several stable isotopes, and radioactive krypton isotopes can be produced by nuclear processes. Krypton gas is not chemically toxic, but like other inert gases it can displace oxygen in enclosed spaces. Compressed and cryogenic krypton also carry pressure and cold hazards.
Why it matters
Krypton matters because it shows how a rare, mostly inert element can still have practical value. Its light emission, low thermal conductivity, isotopes, and chemical quietness make it useful in places where ordinary air, nitrogen, argon, or neon do not quite fit the job.