All practice pages/Interatomic theory/Elements
Element 36, a noble gas
A hidden noble gas that once defined the length of a meter, and that does, reluctantly, form a few compounds.
Period 4, group 18. The other noble gases are tinted, and every cell opens its own article.
A full valence shell, so krypton is very unreactive. Under extreme conditions it does form a few compounds with fluorine, such as krypton difluoride.
About 1 part per million of air, collected when air is liquefied and separated.
William Ramsay and Morris Travers found it in May 1898 in the last traces left after liquid air evaporated, weeks before they found neon and xenon. They named it from the Greek kryptos, hidden.
Insulating gas in energy-efficient windows, some fluorescent and high-performance lamps, camera flashes, and krypton fluoride lasers for research. From 1960 to 1983 the meter was defined by the wavelength of orange-red light given off by krypton-86.