Krypton
. Krypton (Greek kryptos, “hidden”), symbol Kr, colorless, odorless gaseous element that makes up a tiny fraction of the earth's atmosphere . In group 18 (or VIIIa) of the periodic table , krypton is one of the noble gases . The atomic number of krypton is 36. Krypton was first isolated in 1898 by the British chemists Sir William Ramsay and Morris William Travers by fractional distillation of a mixture of the noble gases. Krypton is present in the atmosphere to the extent of 1 part in 20 million by volume or 1 part in 7 million by weight. Several compounds of krypton were discovered in 1962 and 1963. Krypton melts at -157.21° C (-250.98° F) and boils at -153.35° C (-244.03° F); liquid krypton has a specific gravity of 2.41 at its boiling point. The atomic weight of krypton is 83.80. Krypton is used alone or with argon and neon in incandescent bulbs. It emits a characteristic bright, orange-red color in an electric-discharge tube; such tubes filled with krypton are used in light