Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Krypton

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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 lighting airfields because the red light is visible for long distances and penetrates fog and haze to a greater extent than ordinary light. In 1960 the International Commission on Weights and Measures adopted as the length of the standard meter 1,650,763.73 wavelengths of light emitted by the isotope krypton-86. In 1983 the meter was redefined as the distance traveled by light in vacuum in 1/299,792,458 of a second.