Rubidium (Rb): Properties & Uses


Rubidium element

Rubidium is one of the rarest and expensive metals in the world. It is a chemical element with the symbol ‘Rb’ and classified as alkali earth metal (group 1) in the periodic table. Its name comes from the Latin word rubidus, meaning deep red, the colour of its emission spectrum. Its atomic number is 37 and has a standard atomic weight of 85.4678. It is very soft, silvery-white metal and cannot be stored under atmospheric oxygen, due to highly exothermic reaction, sometimes even resulting in the metal catching fire.


Physical Properties

It is a very soft, ductile, silvery-white metal. It reacts violently with water. This reaction is vigorous enough to ignite hydrogen gas it produces. It has also been reported to ignite spontaneously in air. It forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not with lithium (even though rubidium and lithium are in the same group.) It also shows a similar purple colour as potassium show in the flame test. It melts at a temperature of 39.3-degree celsius.

Rubidium metal

Partially molten rubidium metal in an ampoule (small sealed glass capsule)

Chemical Properties

It is one of the most active elements. It catches fire when exposed to oxygen in the air. Due to this reason, it must be stored completely submerged under kerosene. It forms a number of oxides when exposed to air, including rubidium monoxide (Rb2O), Rb6O, and Rb9O2; rubidium in excess oxygen gives the superoxide RbO2. Also, it combines violently with halogens (fluorine, chlorine, bromine, and iodine) and forms salts with halides, producing rubidium fluoride, rubidium chloride, rubidium bromide, and rubidium iodide. It also reacts vigorously with water, as it produces hydrogen gas which catches fire. Also, it combines violently with halogens (fluorine, chlorine, bromine, and iodine.)


Rubidium in the earth’s crust composed of two isotopes: the stable Rubidium-85 and the radioactive Rubidium-87. Additional 24 rubidium isotopes have been synthesized with a half-life less than 3 months, most are highly radioactive and have few uses. As Rubidium-87 beta decays to stable Strontium-87, rubidium has been extensively used in dating rocks.

Rubidium isotopes


It occurs naturally in the minerals leucite, pollucite, carnallite, and zinnwaldite, which contain as much as 1% rubidium oxide. Some potassium minerals and potassium chlorides also contain the element in commercially significant quantities. In seawater, rubidium is the 18th most abundant element. During magma crystallization, rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last. The two significant sources of rubidium in the world are pollucite at Bernic Lake, Manitoba, Canada, and the rubicline ((Rb, K)AlSi3O8) found as impurities in pollucite on the Italian island of Elba, with a rubidium content of 17.5%.

Rubidium in minerals

Rubidium in minerals


1) Specialty Glasses

Speciality glasses, which constitute the leading market for rubidium are used in fibre optics telecommunications systems and in night-vision devices. The carbonate (Rb2CO3) is used as an additive to these types of glass, where it reduces electrical conductivity and improve stability and durability.

Rubidium in optic fibre communication

2) Photoelectric Cells

A rubidium-tellurium photoemissive surface is used in photoelectric cells, which are incorporated in a variety of electronic detection and activation devices. It is due to the photoemission property of rubidium, which is that of surface-emitting free electrons when impinged upon by electromagnetic radiation.

Photoelectric cell

Photoelectric cell

3) Medical Imaging Equipment

A rubidium-caesium-antimony coating is commonly applied to the photocathodes of photomultiplier tubes, which are used in radiation detection devices, medical imaging equipment.

Medical imaging equipment

Medical imaging equipment


4) Rubidium Chloride Uses

Rubidium chloride (RbCl) and several other rubidium salts are used as density gradient media in the ultracentrifugal separation of viruses and the nucleic acids DNA and RNA. It is also used as a biomarker (anything that can be used as an indicator of particular disease state) because, in nature, it is found only in small quantities in living organisms. For example, it is tested for the influence on depression. Dialysis patient suffering from depression show depletion in rubidium and; therefore, supplementation may help during the depression.

Rubidium as Biomarker

Rubidium as Biomarker

5) Rubidium-82 in Positron Emission Tomography (PET)

Rubidium-82 is used for positron emission tomography (a functional imaging technique that uses a radioactive substance to visualize and measure changes in metabolic processes and other physiological activities including blood flow, regional chemical composition, absorption.). • Radiation from 82Rb, which is a decay product of 82Sr, is used in positron emission tomographic (PET) imaging. The rubidium isotope is one of several used in PET, but it is especially well suited for assessing regional blood flow in the heart (myocardial perfusion) and detecting coronary artery disease. Rubidium is very similar to potassium, and tissue with high potassium content will also accumulate the radioactive rubidium. One of the main uses is myocardial perfusion imaging. As a result of changes in the blood-brain barrier in brain tumours, rubidium collects more in brain tumours than normal brain tissue, allowing the use of radioisotope rubidium-82 in nuclear medicine to locate and image brain tumours. PET imaging is also used in imaging the treatment of Epilepsy.

Positron Emission Tomography Scan

Positron Emission Tomography Scan

6) Satellite Navigation and Communication

The resonant frequency of Rubidium-87 atom is used as the reference frequency in frequency standards and oscillators used in radio and television transmitters, for telecommunication network synchronization, and for satellite navigation and communication.

Satellite Navigation

Satellite Navigation

7) Atomic Clocks

Rubidium, which is sometimes used interchangeably with caesium, has been used to make a new kind of atomic clock. Atomic clocks are the most accurate time and frequency standards are known and are used as a frequency standard for international time distribution services, to control the wave frequency of television broadcasts, and in global navigation satellites systems such as GPS. It with further development is expected to achieve an accuracy of 1 part in 1016, which is better than the best timekeeping yet attained.

Rubidium Atomic clocks

8) Other Uses of Rubidium and its Salts

  1. Rubidium iodide (RbI) has sometimes substituted for potassium-iodide (KI) in treating enlargement of the thyroid gland (goitre.)
  2. Rubidium salts have been used as antishock agents following the administration of arsenical drugs.
  3. Radioactive rubidium is used as a tracer of blood flow.
  4. Traces of rubidium have been used as chemical tags for identification and tracing of manufactured goods of various kinds.
  5. Rb2CO3 has been used in the production of certain synthetic fibres.
  6. Rubidium has been used as a cocatalyst for some organic reactions.

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