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Cesium (Cs)

a yellow/silvery alkali metal



atomic number 55
atomic weight 132.9055 cmu

One of only four metals to be liquid at room temperature (gallium, francium, and mercury being the others), cesium's melting point of 83.2 F (28.45 C) is the second lowest of all elements; it boils at 1,253.12 F (671 C).

An extremely reactive element, cesium must be kept under an inert liquid or gas in a vacuum. It will explode on contact with water and produce cesium mydroxide, the strongest base known (it is so strong that it can quickly corrode glass). It also readily combines with oxygen.

Occurence and Sources

Elemental cesium is most commonly found in the minerals pollucite and lepidolite. Those minerals are crushed and heated with sodium metal to 650 C, forming an alloy that can then be separated with a process known as fractional distillation. More than two-thirds of world's reserves of cesium minerals are in Bernic Lake, Manitoba, Canada.

Cesium is more commonly produced as a byproduct of lithium metal production. Due to its reactive nature, cesium is usually sold in the form of cesium azide (CsN3), with the cesium subsequently recovered through heating.


The most well-known use of cesium is as the "mechanism" behind the "world atomic clock," which is accurate to 1 second in 60 million years.

Its readiness to bind with oxygen makes cesium an ideal "getter," a substance that combines with and removes gases from vacuum tubes.

Cesium is also used in photoelectric cells and as a catalyst in the hydrogenation of organic compounds.

Cesium chloride (CsCl) and cesium nitrate (CsNO3) are used in the production of other chemicals.


Cesium was discovered by German chemists Robert Bunsen and Gustav Kirchhoff in 1860, in Heidelberg, Germany, during the spectroscopic analysis of Durkheim mineral water. They named it "cesium," which is from the Latin word caesius, meaning "sky blue," after the blue lines they saw in the spectrum.


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The Robinson Library >> Science >> Chemistry >> Chemical Elements

This page was last updated on 06/19/2017.