Atomic Mass
132.90545196 u
Density
1.93 g/cm³ (at 20 °C)
Discovery
Cesium was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff in Germany using the newly developed technique of spectroscopy.
Common Uses
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Used in atomic clocks, which are extremely accurate timekeeping devices.
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Cesium-137, a radioactive isotope, is used in medical radiation therapy and industrial gauges.
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Used in photoelectric cells.
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Used in some infrared lamps.
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Used as a propellant in ion propulsion systems for spacecraft.
Interesting Facts
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Cesium is a soft, silvery-gold alkali metal that is extremely reactive. It ignites spontaneously in air and reacts explosively with water.
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It was the first element discovered using spectroscopy; its existence was predicted based on blue lines in a spectrum of mineral water.
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The name "cesium" comes from the Latin word "caesius," meaning "sky-blue," referring to the blue lines in its spectrum.
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Cesium has one of the lowest melting points of all metallic elements.
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