Rubidium
The deep red alkali metal discovered by flame spectroscopy.
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Rubidium is a chemical element with the symbol Rb and atomic number 37, belonging to the alkali metal group. It is a very soft, whitish-grey solid, chemically similar to potassium and caesium, and is the first alkali metal with a density greater than water. Natural rubidium on Earth consists of two isotopes: about 72% is stable rubidium-85, while the remaining 28% is the slightly radioactive rubidium-87, which has a half-life of 48.8 billion years—more than three times the estimated age of the universe.
The element was discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff using the then-new technique of flame spectroscopy. Its name derives from the Latin word for deep red, referencing the color of its emission spectrum. Rubidium metal is easily vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms. Although rubidium is not a known nutrient for any living organism, its ions share similar properties and the same charge as potassium ions, so animal cells actively take them up and process them in analogous ways.
Chemical properties
Physically, rubidium is very soft, ductile, and silvery-white, melting at 39.3 °C and boiling at 688 °C. It forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not with lithium. Chemically, it is the second most electropositive stable alkali metal, with a very low first ionization energy of 403 kJ/mol and an electron configuration of [Kr]5s1. It reacts explosively with water, producing rubidium hydroxide and hydrogen gas; being denser than potassium, it sinks in water, and the reaction is often vigorous enough to ignite the metal or hydrogen. Rubidium also ignites spontaneously in air.
Compounds
Its most common compound, rubidium chloride, is used to induce cells to take up DNA and as a biomarker. Other notable compounds include rubidium hydroxide, rubidium carbonate for optical glasses, and rubidium silver iodide, which has the highest room temperature conductivity of any known ionic crystal. Rubidium forms several oxides when exposed to air, including the superoxide in excess oxygen, and salts with all halogens.
Quick Facts
- Atomic number
- 37
- Discovered by
- Robert Bunsen and Gustav Kirchhoff
- Group
- alkali metal
- Melting point
- 39.3 °C
Facts from the source article.
Lore & Background
Rubidium is a chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid belonging to the alkali metal group, closely resembling potassium and caesium. Notably, it is the first alkali metal with a density greater than water. The element was discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff using flame spectroscopy, and its name derives from the Latin word for deep red, referencing the color of its emission spectrum.
Rubidium is highly reactive: it is the second most electropositive stable alkali metal and has a very low first ionization energy. It reacts explosively with water, producing rubidium hydroxide and hydrogen gas, and can ignite spontaneously in air. Its melting point is 39.3 °C, and it boils at 688 °C. Rubidium forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not with lithium.
In nature, rubidium consists of two isotopes: about 72% stable rubidium-85 and 28% slightly radioactive rubidium-87, which has a half-life of 48.8 billion years. It is not abundant, ranking as the 23rd most common element in Earth’s crust, and occurs in minerals such as leucite, pollucite, carnallite, zinnwaldite, and lepidolite, the latter being the commercial source. Rubidium compounds, like rubidium chloride, are used to induce cells to take up DNA and as biomarkers, while rubidium silver iodide has the highest room temperature conductivity of any known ionic crystal. It is not a nutrient for any living organism, but rubidium ions are actively taken up by animal cells similarly to potassium ions.
Reader's Guide
Rubidium is a very soft, ductile, silvery-white metal. It has a melting point of 39.3 °C and a boiling point of 688 °C. It forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not lithium. Rubidium reacts explosively with water to produce rubidium hydroxide and hydrogen gas.
It has a very low first ionization energy of only 403 kJ/mol. Rubidium chloride is probably the most used rubidium compound. Rubidium is not a known nutrient for any living organisms, but rubidium ions have similar properties and the same charge as potassium ions, and are actively taken up and treated by animal cells in similar ways.
Frequently Asked Questions
Who is Rubidium?
Rubidium (Rb, atomic number 37) is a soft, silvery-white alkali metal sitting in Group 1 of the periodic table. It sits just below potassium and above cesium, making it part of the famously reactive 'first column' family.
What is Rubidium known for?
As an alkali metal, Rubidium reacts explosively with water and ignites on its own in moist air, so it must be stored under oil. Its melting point is a mere 39.3 °C, meaning it can soften in a warm hand—far lower than most metals.
What is Rubidium's origin story?
Robert Bunsen and Gustav Kirchhoff spotted Rubidium in 1861 by running mineral samples through a flame and reading the deep-red lines in the emission spectrum. They named it from the Latin 'rubidus,' meaning deep red, after that signature crimson glow.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Rubidium (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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