page_title: Rubidium
section_title: Compounds
hierarchical_section_title: Rubidium / Characteristics / Compounds
caption_attribution_description: Rb9O2 cluster confacial octahedra in Rb suboxides
context_page_description: Rubidium is the chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group. Rubidium metal shares similarities to potassium metal and caesium metal in physical appearance, softness and conductivity. Rubidium cannot be stored under atmospheric oxygen, as a highly exothermic reaction will ensue, sometimes even resulting in the metal catching fire.
  Rubidium is the first alkali metal in the group to have a density higher than water, so it sinks, unlike the metals above it in the group. Rubidium has a standard atomic weight of 85.4678. On Earth, natural rubidium comprises two isotopes: 72% is a stable isotope ⁸⁵Rb, and 28% is slightly radioactive ⁸⁷Rb, with a half-life of 49 billion years—more than three times as long as the estimated age of the universe.
  German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed technique, flame spectroscopy. The name comes from the Latin word rubidus, meaning deep red, the color of its emission spectrum. Rubidium's compounds have various chemical and electronic applications.
context_section_description: Rubidium chloride (RbCl) is probably the most used rubidium compound: among several other chlorides, it is used to induce living cells to take up DNA; it is also used as a biomarker, because in nature, it is found only in small quantities in living organisms and when present, replaces potassium. Other common rubidium compounds are the corrosive rubidium hydroxide (RbOH), the starting material for most rubidium-based chemical processes; rubidium carbonate (Rb₂CO₃), used in some optical glasses, and rubidium copper sulfate, Rb₂SO₄·CuSO₄·6H₂O. Rubidium silver iodide (RbAg₄I₅) has the highest room temperature conductivity of any known ionic crystal, a property exploited in thin film batteries and other applications.
  Rubidium forms a number of oxides when exposed to air, including rubidium monoxide (Rb₂O), Rb₆O, and Rb₉O₂; rubidium in excess oxygen gives the superoxide RbO₂. Rubidium forms salts with halides, producing rubidium fluoride, rubidium chloride, rubidium bromide, and rubidium iodide.
caption: Rb
  9O
  2 cluster
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