Rubidium oxide
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| Names | |
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IUPAC name
Rubidium oxide
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| Other names
Rubidium(I) oxide
Dirubidium oxide |
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| Identifiers | |
18088-11-4 
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| ECHA InfoCard | 100.038.161 |
| Properties | |
| Rb2O | |
| Molar mass | 186.94 g/moL |
| Appearance | Yellow solid |
| Density | 4 g/cm3 |
| Melting point | >500 °C |
| Reacts violently to give RbOH | |
| +1527.0·10−6 cm3/mol | |
| Structure | |
| Antifluorite (cubic), cF12 | |
| Fm3m, No. 225 | |
| Tetrahedral (Rb+); cubic (O2−) | |
| Hazards | |
| Main hazards | Corrosive, reacts violently with water |
| Flash point | Non-flammable |
| Related compounds | |
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Other cations
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Lithium oxide Sodium oxide Potassium oxide Caesium oxide |
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Rubidium suboxide Rubidium peroxide Rubidium superoxide |
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Related compounds
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Rubidium hydroxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox 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.
The alkali metal oxides M2O (M = Li, Na, K, Rb) 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 8 coordinate (cubic) and oxide ions 4 coordinate (tetrahedral).
Like other alkali metal oxides, Rb2O is a strong base. Thus, Rb2O reacts exothermically with water to form rubidium hydroxide.
So reactive is Rb2O toward water that it is considered hygroscopic. Upon heating, Rb2O reacts with hydrogen to rubidium hydroxide and rubidium hydride:
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:
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