Electron configuration and elemental properties of cesium.
Electron configuration and elemental properties of cesium.
Credit: Greg Robson/Creative Commons, Andrei Marincas Shutterstock
Atomic Number: 55
Atomic Symbol: Cs
Atomic Weight: 132.9054519
Melting Point: 83.3 F (28.5 C)
Boiling Point: 1,239.8 F (671 C)

Word origin: Cesium, or caesium, was named after the Latin word for the color sky blue, caesius.

Discovery: Cesium was discovered in 1860 by German chemists Robert Bunsen and Gustav Kirchhoff through spectroscopic analysis of mineral water from the Durkheim region of Germany. They named it cesium after the sky-blue lines in its spectrum.

Lepidolite crystal is a source of lithium, rubidium and cesium.
Lepidolite crystal is a source of lithium, rubidium and cesium.
Credit: farbled Shutterstock

Properties of cesium

Cesium is a silvery-white alkali metal that is very soft and ductile. It has the second lowest melting point of all metallic elements and is liquid near room temperature. Besides two bright blue lines in its spectrum, it also has red, yellow and green wavelengths. [See Periodic Table of the Elements]

Cesium reacts aggressively when combined with water and ice to form cesium hydroxide (CsOH). Cesium hydroxide is the strongest base available and can attack glass.

Cesium has more isotopes than any element — 32 — with masses ranging from 114 to 115.

Sources of cesium

Cesium is a relatively rare metal that occurs in lepidolite (also a source of lithium and rubidium), pollucite (which is a hydrated silicate of aluminum and cesium), and some other sources. Bernic Lake, Manitoba, contains one of the world’s largest reserves of cesium.

Cesium is obtained by electrolysis of the fused cyanide. Very pure cesium that is gas-free is obtained through heating cesium azide (CsN3).

Uses of cesium

Cesium easily combines with oxygen and is often used as a “getter” or material that combines with and removes trace gases from vacuum tubes. The element is also used in atomic clocks, photoelectric cells and as a catalyst for the hydrogenation of several organic compounds.

As cesium can be easily ionized, cesium ions could be used as a propellant in ion engines on spacecraft in the future.

(Source: Los Alamos National Laboratory)