What Is Rubidium?
Rubidium is an alkali metal with an atomic number of 37 and an atomic weight of 85.4678. Discovered by Bunsen and Kirchhoff in Germany in 1861, it’s relatively abundant in the Earth’s crust, though rarely found in ore form. Rubidium is typically obtained as a byproduct of refining lithium and is designated as a hazardous material for its spontaneous combustibility.
Uses of Rubidium
Rubidium strengthens glass and enhances its electrical insulation properties, primarily mixed with glass as rubidium carbonate (Rb2CO3). Its applications include use in cathode ray tubes and atomic clocks, though its commercial and industrial uses are limited. Another application is in dating materials, utilizing the Rubidium87 to Strontium87 ratio to determine the materials’ age from their crystallization time.
Properties of Rubidium
A soft, silvery-white metal, rubidium exhibits a dark red color in flame reactions, similar to potassium. It has a low melting point of 39°C and a boiling point of 688°C, with a gaseous state that appears blue. Sharing properties with other alkali metals, Rubidium has the second lowest electronegativity among nonradioactive alkali elements and a low ionization energy of 406 kJ/mol. In compounds, its valence is +1, and Rubidium ions are readily taken up by plant and animal cells.
Structure of Rubidium
At room temperature, rubidium has a density of 1.532 g/cm3 and adopts a body-centered cubic structure. Its electron configuration is [Kr] 5s1. Due to its large ionic radius, rubidium falls into the category of incompatible elements, which are not easily incorporated into the crystals of rock-forming minerals.
Other Information About Rubidium
1. Reactions of Rubidium
Rubidium is more reactive than potassium and sodium, capable of spontaneously combusting in air and quickly oxidizing to form peroxide (Rb2O2) and superoxide (RbO2). It reacts violently with halogens and water, producing hydrogen gas that can ignite and explode. Rubidium can also form alloys with potassium, sodium, cesium, calcium, and gold, and amalgamate with mercury.
2. Natural Rubidium
The 23rd most abundant element in the Earth’s crust, rubidium is found in ores such as leucite, carnallite, pollucite, and zinnwaldite, with concentrations up to 1%. Lithia mica contains 0.3 to 3.5% rubidium, making it a commercial source. Seawater averages 125 μg/L of Rubidium, less than potassium but more than cesium. Major sources include rubidium microcline on the island of Elba, Italy, and porphyritic deposits at Burnick Lake, Canada.
3. Production of Rubidium
Annually, 2-4 tons of Rubidium compounds are produced. Separation from potassium allows for the production of pure rubidium alum through fractional crystallization from rubidium cesium alum.
4. Rubidium Isotopes
There are 24 known isotopes of Rubidium, including the stable isotope 85Rb and the radioactive isotope 87Rb, with natural abundances of 72.2% and 27.8%, respectively. 87Rb, with a half-life of 4.88 x 1010 years, is used for dating as it decays to stable 87Sr. 82Rb, produced from 82Sr decay, has a half-life of 1.273 minutes and is used in positron emission tomography of the heart.