An Overview about the Chemical Element Rubidium


Symbol: Rb

Atomic Number: 37

Atomic Mass: 85.4678 amu (atomic mass units)

Melting Point: 39.31 C (312.46 K, 102.76 F)

Boiling Point: 688.0 C (961.15 K, 1270.4 F)

Number of Protons: 37

Number of Electrons: 37

Number of Neutrons: 48

Classification: Metal

Group Name: Alkali Metal

Crystal Structure: Cubic

Density @ 293 K: 1.532 grams per cubic centimeter

Color: silver

Rubidium was discovered spectroscopically in 1861 by the German chemists Robert Bunsen and Gustav Kirchhoff. They were using a spectroscope to examine a sample of the mineral lepidolite. Within the spectrum they noticed some deep red spectral lines that they realized were due to an undiscovered element. Bunsen in his search for the element managed to precipitate out some salts containing rubidium from spring water. Eventually Bunsen produced some of the pure metal by reducing a sample of rubidium hydrogen tartrate with carbon. Rubidium gets its name from the Latin word “rubidus” which translates as deepest red.

Pure rubidium is a very soft metal and is cut easily with a knife. The element is also highly reactive; it will even react with air. When added to water the reaction produces hydrogen gas and so much heat that the hydrogen will ignite. To prevent reactions with air or water vapor samples of rubidium must be kept in mineral oil. When held in a flame the element will burn with a yellowish violet color.

The element has one stable isotope – rubidium-85. This isotope makes up 72.17% of the total abundance of rubidium. The remaining 27.83% is made up of rubidium-87 which is unstable and has a half-life of 48,100,000,000 years. Other unstable rubidium isotopes with mass numbers that range from 71 to 101 are known.

Because rubidium so reactive it has never been found as a free element in nature. Commercial production of rubidium is as a by-product from the refining of another alkali metal, lithium.

Rubidium has a few industrial uses.

* It is used as a “getter” to remove trace gases from vacuum tubes.

* Rubidium is used in the manufacture of photocells and some special glasses.

* A future application for the element may be in as a propellant for ion drives in spacecraft.

Rubidium makes compounds with many other elements. As yet none of its compounds have any industrial uses. A compound of rubidium, silver and iodine (RbAg4I5) may find an application in the production of thin film batteries. At room temperature it has the highest conductivity of any known ionic crystal.