Rubidium: Occurrence, Properties, Uses, and Isotopes of Rubidium


Rubidium is an alkali metal present in group number 1 of the periodic table. Its atomic number is 37 whereas its atomic mass is 85.46. Rubidium has 37 electrons. It has 37 protons and 48 neutrons in its nucleus. Rubidium is represented by the symbol “Rb”.

Naming and History

The name of rubidium comes from the Latin word “Rubidius” which means “deep red”. The atomic spectra of rubidium showed ruby red lines, that were never seen before. It was named after that spectrum.

Robert Bunsen and Gustav Kirchhoff

In 1861, Robert Bunsen and Gustav Kirchhoff discovered rubidium, in Heidelberg, Germany, by utilizing spectroscopy. Bunsen and also Kirchhoff placed different salts in the fire of the recently invented Bunsen burner.

They saw colored lines in each of the spectra they took. They discovered that these colored lines were unique to whichever substance was burnt. The lines in a range were a method of ‘fingerprinting’ an element (known or not known).


Bunsen extracted rubidium metal from its chloride salt by electrolysis. He found that the rubidium was a lot more electropositive than potassium and decomposed water releasing hydrogen.

Further Reading:  Alkanes [Properties, Structure, Reactivity, and Uses of Alkanes]

A sample of pure rubidium was obtained in 1928.

Occurrence of Rubidium


It is estimated that rubidium is the 16th most abundant element in Earth’s crust. Although it does not have its own minerals. It never occurs as a free element. It is present in other minerals such as carnallite, lepidolite, etc. Trace amounts are also found in leucite, zinnwaldite, etc.

Large amounts of rubidium are obtained as a byproduct of lithium in lithium refining, nowadays.

Properties of Rubidium

Rubidium is a silvery-white, metallic, soft alkali metal. It is considered among one of the most electropositive elements. It exists as solid at room temperature but can easily melt on a hot day as its melting point is 39.31 °C.

The boiling point of rubidium is 688°C. It has a density of 1.53 grams per cubic centimeter. Rubidium ignites spontaneously in the air and can vigorously react with water even with ice. It liberates hydrogen and is set on fire immediately.

Rubidium, like other alkali metals, forms amalgams with mercury. On burning, it produces a yellowish-violet flame.

Rubidium in Biological Systems

There is no known significant role of rubidium in living organisms. However, some researches show its usage in the treatment of depression. The patients of kidney dialysis tend to be depressed and showed reduced levels of rubidium.

Uses of Rubidium 

Rubidium has not a wide range of uses. But some of them are given:

  • It is used to remove traces of oxygen and residual gases from vacuum tubes.
  • Rubidium is used in making special types of glasses and manufacturing photocells.
  • Rubidium is used in fireworks, pyrotechnics to give them purple color.
  • It is used in ceramics.
  • The compound of rubidium, iodine, silver has characteristic electrical properties and is used in thin-film batteries.
  • It can be easily ionized so used in ion engines of space vehicles.
  • It is used as a working fluid for vapor turbines and thermoelectric generators.
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Isotopes of Rubidium

There are almost 29 known isotopes of rubidium. Two naturally occurring isotopes are Rb- 85 and Rb- 87.

  • Rb- 87 is slightly radioactive and used in locating tumors in the brain and in the precise dating of rocks.