caesium(redirected from Element 55)
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Related to Element 55: Element 66
n. Chiefly British
Variant of cesium.
(Elements & Compounds) a ductile silvery-white element of the alkali metal group that is the most electropositive metal. It occurs in pollucite and lepidolite and is used in photocells. The radioisotope caesium-137, with a half-life of 30.2 years, is used in radiotherapy. Symbol: Cs; atomic no: 55; atomic wt: 132.90543; valency: 1; relative density: 1.873; melting pt: 28.39±0.01°C; boiling pt: 671°C
ce•si•um(ˈsi zi əm)
a rare highly reactive soft metallic element of the alkali metal group used chiefly in photoelectric cells. Symbol: Cs; at. wt.: 132.905; at. no.: 55; sp. gr.: 1.9 at 20°C; melts at 28.5°C.
[1861; < Latin caesium, neuter of caesius bluish gray (see -ium2); so named from the blue lines in its spectrum]
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|Noun||1.||caesium - a soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal|
metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
cesium 137 - a radioactive isotope of cesium used in radiation therapy
pollucite - a rare mineral that is an important source of cesium