 | |
| Names | |
|---|---|
| IUPAC name Rubidium oxide | |
| Other names Rubidium(I) oxide Dirubidium oxide | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
| 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 to giveRbOH | |
| +1527.0·10−6 cm3/mol | |
| Structure | |
| Antifluorite (cubic),cF12 | |
| Fm3m, No. 225 | |
| Tetrahedral (Rb+); cubic (O2−) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Corrosive, reacts violently with water |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Related compounds | |
Otheranions | Rubidium sulfide Rubidium selenide Rubidium telluride Rubidium polonide |
Othercations | Lithium oxide Sodium oxide Potassium oxide Caesium oxide |
| Rubidium suboxide Rubidium peroxide Rubidium sesquioxide Rubidium superoxide Rubidium ozonide | |
Related compounds | Rubidium hydroxide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Rubidium oxide is thechemical compound with theformulaRb2O. Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally. The rubidium content inminerals is often calculated and quoted in terms ofRb2O. In reality, the rubidium is typically present as a component of (actually, an impurity in)silicate oraluminosilicate. A major source of rubidium islepidolite,KLi2Al(Al,Si)3O10(F,OH)2, wherein Rb sometimes replaces K.
Rb2O is a yellow colored solid. The related speciesNa2O, K2O, andCs2O are colorless, pale-yellow, and orange, respectively.
Thealkali metal oxidesM2O (M = Li, Na, K, Rb) crystallise in the antifluorite structure. In the antifluorite motif, the positions of theanions andcations are reversed relative to their positions inCaF2, with rubidium ions 4-coordinate (tetrahedral) and oxide ions 8-coordinate (cubic).[1]
Like other alkali metal oxides, Rb2O is a strongbase. Thus, Rb2O reacts exothermically with water to formrubidium hydroxide.
So reactive is Rb2O toward water that it is consideredhygroscopic. Upon heating, Rb2O reacts withhydrogen to rubidium hydroxide andrubidium hydride:[2]
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,[3] the best synthesis of Rb2O doesnot entail oxidation of the metal but reduction of the anhydrous nitrate:
Typical for alkali metal hydroxides, RbOHcannot be dehydrated to the oxide. Instead, the hydroxide can be decomposed to the oxide (by reduction of the hydrogen ion) using Rb metal:
Metallic Rb reacts with O2, as indicated by its tendency to rapidlytarnish in air. The tarnishing process is relatively colorful as it proceeds via bronze-colored Rb6O and copper-colored Rb9O2.[4] Thesuboxides of rubidium that have been characterized byX-ray crystallography include Rb9O2 and Rb6O, as well as the mixedCs-Rb suboxides Cs11O3Rbn (n = 1, 2, 3).[5]
The final product of oxygenation of Rb is principally RbO2,rubidium superoxide:
This superoxide can then be reduced to Rb2O using excess rubidium metal:
