Rubidium oxide is the chemical compound with the formula . 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 . 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, , wherein Rb sometimes replaces K.

is a yellow colored solid. The related species , and are colorless, pale-yellow, and orange, respectively.

The alkali metal oxides crystallise in the antifluorite structure. In the antifluorite motif, the positions of the anions and cations 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.

1. 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:

1. Rb2O + H2 → RbOH + RbH

Synthesis

For laboratory use, RbOH, which is available commercially, is used in place of the oxide. The hydroxide is less reactive than the oxide.

As is the case for potassium oxide, Rb2O can be prepared by thermal reaction of the metal with a deficiency of oxygen:

The Rb reaction with O2 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 include Rb9O2 and Rb6O, as well as the mixed Cs-Rb suboxides Cs11O3Rbn (n = 1, 2, 3).

The product of oxygenation with excess oxygen is principally RbO2, rubidium superoxide:

1. Rb + O2 → RbO2

This superoxide can then be reduced to Rb2O using excess rubidium meta.

Alternatively rubidium metal reacts with mercuric oxide:

Typical for alkali metal hydroxides, RbOH cannot be dehydrated to the oxide.

References

Further reading