Electron configuration and elemental properties of rubidium.
Electron configuration and elemental properties of rubidium.
Credit: Greg Robson/Creative Commons, Andrei Marincas Shutterstock
Atomic Number: 37
Atomic Symbol: Rb
Atomic Weight: 85.4678
Melting Point: 102.7 F (39.3 C)
Boiling Point: 1,270 F (688 C)

Word origin: The word rubidium derives from the Latin rubidus, meaning deepest red.

Discovery: Rubidium was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff. They found it in the mineral lepidolite by using a spectroscope.

Properties of rubidium

At room temperature, rubidium can be a liquid. It is a soft, silvery-white metallic element in the alkali group. [See Periodic Table of the Elements]

Rubidium is the second-most electropositive and alkaline element. As with other alkali metals, it forms amalgams with mercury and alloys with gold, cesium, sodium and potassium. It can ignite spontaneously in air and react violently in water, setting fire to the liberated hydrogen. Its presence colors a flame yellowish violet.

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

As a metal, it can be prepared by reducing rubidium chloride with calcium, in addition to many other methods. Rubidium must be kept under a dry mineral oil or in a vacuum or inert atmosphere.

Sources of rubidium

Several years ago, rubidium was considered to be relatively rare. It has now been discovered to be fairly abundant, the 16th most abundant element in Earth’s crust.

Rubidium occurs in pollucite, leucite and zinnwaldite, which can contain traces up to 1 percent in the form of the oxide. Lepidolite can contain up to 1.5 percent rubidium, and the element can be recovered commercially from this source.

Rubidium can also be recovered commercially from potassium minerals and potassium chloride. It is found, along with cesium, in the extensive pollucite deposits at Bernic Lake, Manitoba.

Rubicline, a mineral with rubidium as an essential constituent, was discovered in Campo, Elba, Italy, in 1998.

Uses of rubidium

Rubidium is useful in high-precision timing and is often the main component in atomic clocks.

Rubidium is used as a getter in vacuum tubes because it combines with and removes trace gases. It is also a component in photocells and has been used in making special glasses.

Rubidium has been considered for use in ion engines in space shuttles, because it can be easily ionized. Cesium, however, is more efficient. It has been proposed that rubidium could be a working fluid for vapor turbines and a thermoelectric generator through the magnetohydrodynamic principle that would cause rubidium ions to be formed by high-temperature heats.

Rubidium silver iodide (RbAg4I5) could possibly be used in thin film batteries and other applications, because it has the highest room conductivity of any known crystal. At 20 C (68 F), its conductivity is about the same as dilute sulfuric acid.

One of the most important rubidium compounds, rubidium chloride (RbCl), is used in biochemistry.


There are 24 known isotopes of rubidium. Naturally occurring rubidium is made of two isotopes, 85Rb and 87Rb. Rubidium-87 is present to the extent of 27.85 percent in natural rubidium and is a beta emitter with a half-life of 4.9 x 1010 years. Ordinary rubidium is radioactive enough to expose a photographic film in about 30 to 60 days. Rubidium forms four oxides: Rb2O, Rb2O2, Rb2O3, Rb2O4.

(Source: Los Alamos National Laboratory)