Rubidium Rubidium is located between potassium and cesium in the first Group on the Periodic Table. It's atomic number is 37and its atomic mass is 85.4678. In French and German it is rubidium, in Italian and Spanish it is rubidio. History and General Facts Rubidium was discovered spectroscopically in1861 by Robert Bunsen and Gustav Kirchhoff in Germany. They experimented with spectral lines of light, now called spectroscopy. They noticed that, when heated or burned, different elements produced distinctive colors of light when transmitted through a prism. One element in the mineral lepidolite, when heated, produced a distinct red line, thi