Rubidium oxide is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

. Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally. The rubidium content in

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

s is often calculated and quoted in terms of . In reality, the rubidium is typically present as a component of (actually, an impurity in)

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is a ...

aluminosilicate Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals. Andalusite, kyanite, and sillimanite are naturall ...

. A major source of rubidium is

lepidolite Lepidolite is a lilac-gray or rose-colored member of the mica group of minerals with chemical formula . It is the most abundant lithium-bearing mineral and is a secondary source of this metal. It is the major source of the alkali metal rubidium. ...

, , wherein Rb sometimes replaces K. is a yellow colored solid. The related species , and are colorless, pale-yellow, and orange, respectively. The

alkali metal oxide The alkali metals react with oxygen to form several different compounds: suboxides, oxides, peroxides, sesquioxides, superoxides, and ozonides. They all react violently with water. Alkali metal suboxides * Hexarubidium monoxide (Rb6O) h * No ...

s crystallise in the antifluorite structure. In the antifluorite motif the positions of the

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s and

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s are reversed relative to their positions in CaF₂, with rubidium ions 4-coordinate (tetrahedral) and oxide ions 8-coordinate (cubic).

Properties

Like other alkali metal oxides, Rb₂O is a strong base. Thus, Rb₂O reacts exothermically with water to form

rubidium hydroxide Rubidium hydroxide is the inorganic compound with the formula RbOH. It consists of rubidium cations and an equal number of hydroxide anions. It is a colorless solid that is commercially available as aqueous solutions from a few suppliers. Like ot ...

. :Rb₂O + H₂O → 2 RbOH So reactive is Rb₂O toward water that it is considered

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...

. Upon heating, Rb₂O reacts with

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

to rubidium hydroxide and rubidium hydride: :Rb₂O + H₂ → RbOH + RbH

Synthesis

For laboratory use, RbOH is usually used in place of the oxide. RbOH can be purchased for ca. US$5/g (2006). The hydroxide is more useful, less reactive toward atmospheric moisture, and less expensive than the oxide. As for most alkali metal oxides, the best synthesis of Rb₂O does ''not'' entail oxidation of the metal but reduction of the anhydrous nitrate: :10 Rb + 2 RbNO₃ → 6 Rb₂O + N₂ Typical for alkali metal hydroxides, RbOH ''cannot'' be dehydrated to the oxide. Instead, the hydroxide can be decomposed to the oxide (by reduction of the hydrogen ion) using Rb metal: :2 Rb + 2 RbOH → 2 Rb₂O + H₂ Metallic Rb reacts with O₂, as indicated by its tendency to rapidly tarnish in air. The tarnishing process is relatively colorful as it proceeds via bronze-colored Rb₆O and copper-colored Rb₉O₂. The suboxides of rubidium that have been characterized by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

include Rb₉O₂ and Rb₆O, as well as the mixed Cs-Rb suboxides Cs₁₁O₃Rb_''n'' (''n'' = 1, 2, 3). The final product of oxygenation of Rb is principally RbO₂,

rubidium superoxide Rubidium superoxide or Rubidium hyperoxide is a compound with the formula . In terms of oxidation states, the negatively charged superoxide and positively charged rubidium give it a structural formula of (Rb+)(O2−). Chemistry It can be created b ...

: :Rb + O₂ → RbO₂ This superoxide can then be reduced to Rb₂O using excess rubidium metal: :3 Rb + RbO₂ → 2 Rb₂O

Properties

Synthesis

References

Further reading