- Rubidium (Rb) is an alkali metal with atomic number 37, located in Group 1 of the periodic table between potassium and cesium.
- It is a soft, silvery-white metal that is highly reactive, rapidly oxidizing in air and reacting violently with water to produce hydrogen gas and rubidium hydroxide (RbOH), a strongly alkaline solution.
- Rubidium has one valence electron in the 5s subshell, which it readily loses to form the +1 oxidation state, its only common ionic form. Its atomic structure consists of thirty-seven protons, typically forty-eight neutrons, and thirty-seven electrons arranged in five shells.
- Naturally occurring rubidium is composed of two isotopes: rubidium-85 (⁸⁵Rb, 72.17%) and rubidium-87 (⁸⁷Rb, 27.83%). Rubidium-87 is mildly radioactive, with a half-life of about 4.88 × 10¹⁰ years, making it useful in geologic dating methods such as rubidium–strontium dating.
- Rubidium is relatively abundant in the Earth’s crust at about 90 parts per million, making it more common than lithium. However, it does not occur in native metallic form due to its reactivity. Instead, it is found dispersed in minerals such as lepidolite, pollucite, carnallite, and zinnwaldite, often alongside potassium and cesium. Commercial production of rubidium is typically as a by-product of lithium extraction from lepidolite or pollucite ores. Major sources are found in Canada, the United States, Namibia, and parts of Europe.
- The element was discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff using flame spectroscopy. They identified new spectral lines in the blue region and named the element from the Latin rubidus, meaning “deep red,” referring to the prominent red lines in its emission spectrum.
- Due to its rarity and high reactivity, rubidium has limited large-scale industrial use, but it has specialized applications in electronics, research, and materials science. Rubidium compounds are used in specialty glasses, including those for fiber optics, to improve refractive properties. Rubidium is also employed in atomic clocks—rubidium frequency standards—where it provides a compact and less expensive alternative to cesium clocks for applications requiring precise timing, such as telecommunications and GPS systems.
- In scientific research, rubidium is used in laser cooling and trapping experiments, where rubidium atoms are slowed and confined using tuned laser light for studies in quantum mechanics, Bose–Einstein condensates, and atomic physics. Rubidium isotopes also serve as chemical and tracer markers in various biochemical and geological investigations.
- Chemically, rubidium behaves similarly to other alkali metals but is even more reactive than potassium and slightly less reactive than cesium. It forms ionic salts with halogens, oxides, and other nonmetals, and can form amalgams with mercury. In the presence of oxygen, it can form rubidium oxide (Rb₂O), rubidium peroxide (Rb₂O₂), and rubidium superoxide (RbO₂) depending on conditions.
- Biologically, rubidium has no essential role in humans or animals, but the body can take up small amounts in place of potassium due to similar ionic sizes. While not particularly toxic, high doses of rubidium salts can interfere with potassium-dependent biological processes.
- From an environmental standpoint, rubidium is not considered hazardous in trace natural concentrations, but due to its reactivity, the metal itself must be stored under inert gas or mineral oil to prevent ignition or explosive reactions with moisture.
