rubidium

Rubidium is a chemical element with atomic number 37 and the symbol Rb. It is a soft, ductile, whitish-gray alkali metal. Rubidium had few applications until the 1920s, but since then the element has had wide variety of uses, from giving fireworks a purple color to a component of atomic clocks. Rubidium-87 was used to produce a Bose-Einstein condensate in 1996, which earned the scientists a Nobel Prize in 2001.

Rubidium was discovered in 1860 by Gustav Kirchhoff and Robert Bunsen. It was discovered simultaneously with cesium. These two elements were the first ones discovered through spectrography. The pair took the name from the Latin rubidus (red), due to the two distinct lines in the red portion of the visual spectrum. The pair wrote in their 1861 announcement of their discovery:

Unter denselben sind besonders zwei rothe dadurch merkwürdig, dass sic tiorh jenseits der Fraunhofer'schen Linie A oder der mit dieser zusammenfallenden Linie Ka ɑ, also im alleräufsersten Hoth des Sonnenspetrums liegen. Wir schlagen daher für dieses Alkalimetall, mit Beziehung auf jene besonders merkwürdigen dunkelrothen Spectrallinien die Benennung Rubidium vor mit dem Symbol Rb, von rubidus, welches von den Alten für das dunkelste Roth gebraucht wird.

(Among them, two red ones are particularly remarkable in that they lie far beyond Fraunhofer's line A or the line Ka ɑ that coincides with it, and thus in the very outermost region of the solar spectrum. We therefore propose the name rubidium for this alkali metal, with reference to those particularly remarkable dark red spectral lines, with the symbol Rb, from rubidus, which is used by the ancients for the darkest red.)

Sources:

Kirchhoff, G. and R. Bunsen. “Chemische Analyse durch Spectralbeobachtungen” (June 1861). Annalen der Physik, 189.7, 1861, 337–81 at 339. DOI: 10.1002/andp.18611890702.

Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022. DOI: 10.1007/s10698-022-09451-w.

Oxford English Dictionary, third edition, March 2011, s.v. rubidium, n.

Photo credit: Tomihahndorf, 2006. Wikimedia Commons. Public domain photo.