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Rubidium oxide

Systematic name Rubidium oxide
Other names Rubidium(I) oxide
Dirubidium oxide
Molecular formula Rb2O
Molar mass 186.935 g/moL
Appearance Yellow or brown solid
CAS number [18088-11-4]
Density and phase 4000 kg m-3 when solid
Solubility in water Reacts with water
Melting point Decomposes at
400°C / 673K
Basicity -4
Main hazards Reacts violently with water
Related compounds
Other anions Rubidium fluoride
Rubidium chloride
Rubidium bromide
Rubidium iodide
Rubidium hydride
Rubidium hydroxide
Rubidium oxide
Rubidium sulfide
Rubidium selenide
Rubidium telluride
Other cations Lithium oxide
Sodium oxide
Potassium oxide
Caesium oxide
Francium oxide
and all other oxides
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Rubidium oxide is the chemical compound with the formula Rb2O. Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally. The rubidium content in minerals is often calculated and quoted in terms of Rb2O. In reality, the rubidium is typically present as a component of (actually, an impurity in) silicate or aluminosilicate. A major source of rubidium is lepidolite, KLi2Al(Al,Si)3O10(F,OH)2 wherein Rb sometimes replaces K.

Rb2O is a yellow colored solid. The related species Na2O, K2O, and Cs2O are colorless, pale-yellow, and orange, respectively. Like most other alkali metal oxides, Rb2O, adopts the anti-fluorite structure (Cs2O, uniquely for an oxide, adopts the anti-CdCl2 structure).



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

Rb2O + H2O → 2 RbOH

So reactive is Rb2O toward water that it is considered hygroscopic. Upon heating, Rb2O reacts with hydrogen to rubidium hydroxide and rubidium hydride:[4]

Rb2O + H2 → RbOH + RbH


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,[5] the best synthesis of Rb2O does not entail oxidation of the metal but reduction of the anhydrous nitrate:

10Rb + 2 RbNO3 → 6 Rb2O + N2

Typical for alkali metal hydroxides, RbOH cannot be dehydrated to the oxide. Instead, the hydroxide can be reduced to the oxide 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.[5] The suboxides of rubidium that have been characterized by X-ray crystallography include Rb9O2 and Rb6O, as well as the mixed Cs-Rb suboxides Cs11O3Rbn (n = 1, 2, 3).[1]

The final product of oygenation of Rb is principally RbO2, i.e. rubidium superoxide.

Rb + O2 → RbO2

This superoxide can then be reduced to Rb2O using excess rubidium metal:

3 Rb + RbO2 → 2 Rb2O

Safety considerations

Rubidium oxide, like other strongly alkaline compounds, can cause skin burns upon contact See MSDS.


  1. ^ Simon, A. ”Group 1 and 2 Suboxides and Subnitrides — Metals with Atomic Size Holes and Tunnels” Coordination Chemistry Reviews 1997, volume 163, Pages 253-270.doi:10.1016/S0010-8545(97)00013-1
  1. Rubidium oxide at Engineering Database, accessed in August 2005.
  2. Rubidium oxide at WebElements, accessed in December 2005.
  3. Rubidium oxide at Fisher Scientific, accessed in August 2005.
  4. H. Nechamkin, The Chemistry of the Elements, p 34; McGraw-Hill, New York, 1968.
  5. A. F. Holleman, E. Wiberg, "Inorganic Chemistry" Academic Press: San Diego, 2001.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Rubidium_oxide". A list of authors is available in Wikipedia.
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