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Atomic symbol Kr
Atomic number 36
Classification Noble Gas
Atomic mass 83.8 amu
Number of Stable Isotopes 6
Density (grams per cc) .0037493 g/cm^3
Other Information
Date of discovery 1898
Name of discoverer Sir William Ramsay and M. W. Travers
Name origin From the Greek word kryptos, hidden
Uses Lighting and scientific standards
Obtained from Production of liquid air

Krypton is an element in the "noble gas" class (or "inert gas") of the periodic table. It is colorless and odorless. It is almost (but not completely) chemically inert. Its density as a gas (at standard temperature and pressure) is .0037493 g/cm^3, about 3 times that of air. As a solid (below 116 degrees K) its density is 2.823 g/cm^3.

It is noteworthy in that, between 1960 and 1983, one of its spectral lines was used as the official scientific definition of length—1 meter was 1650763.73 wavelengths. (Prior to that, the meter was defined as the distance between two lines scratched on the "International Standard Meter stick". Since 1983, the unit of length has been defined in terms of time.)