Cesium

Robert Bunsen (the German chemist who invented the Bunsen burner) and Gustav Kirchhoff (a German physicist best known for his work on electrical circuits and “blackbody” radiation from heated objects) discovered cesium together by flame spectroscopy.

Spectroscopy is a method of chemical identification based on the specific colors (wavelengths) of light emitted or absorbed by an element. It was done with a spectroscope, which Bunsen and Kirchhoff invented one year earlier. Their spectroscopic observations of flames from evaporated mineral water from Dürkheim, Germany, included a combination of several prominent blue lines (specific shades of blue) that had not been seen by spectroscopy before. Bunsen and Kirchhoff concluded that there was a new element present and named it after the latin word caesius, which means bluish gray. Cesium was the first element to be discovered by spectroscopy.

While spectroscopy made it possible for Bunsen and Kirchhoff to identify cesium, their efforts to isolate the element were unsuccessful. It was first isolated in 1882 by Swedish chemist Carl Setterberg.

Cesium is a shiny alkali metal with a pale gold color. Alkali metals form the first column of the periodic table. Like the other alkali metals, cesium is ductile (stretchable) and soft enough to be cut with a knife.

Unlike most other metals, cesium has a very low melting point; it is a shiny metallic liquid above 28.5°C, slightly above room temperature. Only five metals are liquid at or near room temperature. The other four are gallium, mercury, rubidium, and francium. Rubidium and francium sit immediately above and below cesium on the periodic table.

Cesium is extremely reactive. It reacts explosively with water, especially cold water, sometimes shattering the water container. It is so reactive because it is the most electropositive element. That means it is the most likely of all the elements donate an electron to another element, making that element into a negative ion and making cesium into a positive ion so the two can form an ionic bond between them.

It is also the most alkaline (highest pH) element. It is a strong enough base that it eats through glass.

The most well-known application of cesium is the atomic clock. The most accurate clock—indeed, the most accurate measurement of any kind—relies on electromagnetic transitions between two states in the cesium atom, using the cesium-133 isotope. Modern cesium atomic clocks are so accurate that they would only lose or gain one second every 20 million years. In fact, the behavior of cesium forms the basis for the modern definition of one second.

The compound cesium formate is widely used as an environmentally friendly well-drilling fluid in oil extracting.

Cesium metal is used in photoelectric cells and as a catalyst in the hydrogenation of certain organic compounds. Cesium is also used in a variety of scientific instruments and other electronic, industrial, and medical applications.

Cesium comes primarily from a whitish mineral called pollucite. A particularly rich source of pollucite is located at Bernic Lake, Manitoba. The deposits are estimated to contain 300,000 tons of pollucite, averaging 20 percent cesium. The cesium can be isolated by electrolysis (chemical separation via electric current) and other methods.