Rubidium oxide

{{chembox

| verifiedrevid = 380552214

| ImageFile = Rubidium-oxide-xtal-3D-vdW-B.png

| IUPACName = Rubidium oxide

| OtherNames = Rubidium(I) oxide
Dirubidium oxide

|Section1={{Chembox Identifiers

| CASNo = 18088-11-4

| CASNo_Ref = {{cascite|correct|CAS}}

| ChemSpiderID = 8329869

| PubChem = 10154361

| SMILES = [Rb+].[O-2].[Rb+]

| StdInChI=1S/O.2Rb/q-2;2*+1

| StdInChIKey = YIONJVUULJNSMK-UHFFFAOYSA-N

}}

|Section2={{Chembox Properties

| Formula = Rb₂O

| MolarMass = 186.94 g/moL

| Appearance = Yellow solid

| Density = 4 g/cm³

| Solubility = Reacts to give RbOH

| MeltingPt = >500 °C

| MagSus = +1527.0·10⁻⁶ cm³/mol

}}

|Section3={{Chembox Structure

| CrystalStruct = Antifluorite (cubic), cF12

| SpaceGroup = Fm3m, No. 225

| Coordination = Tetrahedral (Rb⁺); cubic (O²⁻)

| LattConst_a =

| LattConst_alpha =

}}

|Section4={{Chembox Thermochemistry

| DeltaHf =

| Entropy =

| HeatCapacity =

}}

|Section7={{Chembox Hazards

| ExternalSDS =

| MainHazards = Corrosive, reacts violently with water

| NFPA-H = 3

| NFPA-F = 0

| NFPA-R = 1

| NFPA-S = W

| FlashPt = Non-flammable

}}

|Section8={{Chembox Related

| OtherAnions = Rubidium sulfide
Rubidium selenide
Rubidium telluride
Rubidium polonide

| OtherCations = Lithium oxide
Sodium oxide
Potassium oxide
Caesium oxide

| OtherFunction = Rubidium suboxide
Rubidium peroxide
Rubidium sesquioxide
Rubidium superoxide
Rubidium ozonide

| OtherFunction_label = rubidium oxides

| OtherCompounds = Rubidium hydroxide

}}

Rubidium oxide is the chemical compound with the formula {{chem|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 {{chem|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, {{chem|KLi₂Al(Al,Si)₃O₁₀(F,OH)₂}}, wherein Rb sometimes replaces K.

{{chem|Rb₂O}} is a yellow colored solid. The related species {{chem|Na₂O, K₂O}}, and {{chem|Cs₂O}} are colorless, pale-yellow, and orange, respectively.

The alkali metal oxides {{chem|1=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 4-coordinate (tetrahedral) and oxide ions 8-coordinate (cubic).{{cite book |last1= Wells|first1= Alexander Frank|title= Structural Inorganic Chemistry|edition= 5th|year= 1984|publisher= Clarendon Press|location= Oxford|isbn= 978-0-19-855370-0}}

Properties

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:{{cite book |last1= Nechamkin|first1= Howard|title= The chemistry of the elements|url= https://archive.org/details/chemistryofeleme00nech|url-access= registration|year= 1968|publisher= McGraw-Hill|location= New York|page= [https://archive.org/details/chemistryofeleme00nech/page/34 34]}}

: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,{{cite book |editor1-first= A.F.|editor1-last= Holleman|editor2-first= E.|editor2-last= Wiberg|title= Inorganic Chemistry|year= 2001|publisher= Academic Press|location= San Diego|isbn= 978-0-12-352651-9}} 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.{{cite book |editor1-first= A.F.|editor1-last= Holleman|editor2-first= E.|editor2-last= Wiberg|title= Inorganic Chemistry|year= 2001|publisher= Academic Press|location= San Diego|isbn= 978-0-12-352651-9}} The suboxides of rubidium that have been characterized by X-ray crystallography include Rb₉O₂ and Rb₆O, as well as the mixed Cs-Rb suboxides Cs₁₁O₃Rb_n (n = 1, 2, 3).{{Cite journal | last1 = Simon | first1 = A. | doi = 10.1016/S0010-8545(97)00013-1 | title = Group 1 and 2 suboxides and subnitrides — Metals with atomic size holes and tunnels | journal = Coordination Chemistry Reviews | volume = 163 | pages = 253–270 | year = 1997 }}

The final product of oxygenation of Rb is principally RbO₂, rubidium superoxide:

:Rb + O₂ → RbO₂

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

:3 Rb + RbO₂ → 2 Rb₂O

Rubidium oxide

Properties

Synthesis

References

Further reading