The chemical element of atomic number 55, a soft, silvery, extremely reactive metal. It belongs to the alkali metal group and occurs as a trace element in some rocks and minerals. (Symbol: Cs)
- Those that produce a measurable spectrum when subjected to flame include, but are not limited to, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, zinc, and cadmium.
- They also can form condensates out of numerous different elements, including sodium, potassium, lithium, cesium, hydrogen and helium.
- These elements - lithium, sodium, potassium, rubidium, cesium and francium - all react with water to give solutions that change the color of a vegetable dye from red to blue.
Mid 19th century: from Latin caesius 'grayish-blue' (because it has characteristic lines in the blue part of the spectrum).
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