Rubidium cation (22537-38-8) Physical and Chemical Properties
Rubidium cation
Monovalent rubidium (Rb+) cation supplied for use in inorganic salts, analytical standards and specialty R&D applications.
| CAS Number | 22537-38-8 |
| Family | Alkali metal cations / inorganic salts |
| Typical Form | Powder or crystalline solid (as salts) |
| Common Grades | EP |
Rubidium cation is a monovalent inorganic cation belonging to the alkali metal family and represents the singly charged ionic form of the element rubidium. Structurally it is a monoatomic cation with closed-shell noble-gas electronic configuration after loss of the single valence \(5s\) electron; the nominal formula is \(\mathrm{Rb}^+\). As an alkali metal cation, \(\mathrm{Rb}^+\) exhibits low polarizing power relative to smaller, higher-charge cations and is strongly hydrated in aqueous media, forming labile first-shell solvation complexes.
Electronically and chemically, \(\mathrm{Rb}^+\) behaves as a hard, monovalent spectator cation in most aqueous and many nonaqueous systems: it shows negligible Brønsted acidity, minimal hydrolysis, and weak specific interactions with neutral ligands except when selected by size-specific complexants (for example, crown ethers or cryptands). Relative lipophilicity is low for the bare ion; solvation and ion pairing govern partitioning behavior in mixed solvents. Oxidation/reduction behavior is relevant for the metallic element (rubidium metal is highly reducing), whereas the cationic form is chemically stable under typical laboratory and industrial conditions and is commonly encountered as soluble salts.
Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting or Decomposition Point
Listed melting point: \(39\,^\circ\mathrm{C}\). Note that this value corresponds to the metallic element phase transition; melting or decomposition temperatures for salts and complexed forms of \(\mathrm{Rb}^+\) vary widely and are determined by the specific counter‑ion and lattice/solvation structure.
Solubility in Water
No experimentally established value for this property is available in the current data context.
Solution pH (Qualitative Behavior)
As a simple monovalent alkali cation, \(\mathrm{Rb}^+\) is essentially non‑hydrolyzing in water and behaves as a spectator ion in acid–base chemistry. Aqueous solutions of rubidium salts (when prepared from neutral counterions such as chloride, nitrate or sulfate) are typically near neutral pH unless the counterion or dissolved impurities impart acidity or basicity. Significant perturbation of \(\mathrm{pH}\) by \(\mathrm{Rb}^+\) itself is not expected under normal concentrations used in laboratory and industrial processes.
Chemical Properties
Acid–Base Behavior
\(\mathrm{Rb}^+\) is not a proton donor and shows negligible Brønsted acidity; it does not have a measurable \(\mathrm{p}K_a\) associated with deprotonation. In water the ion is strongly solvated but does not undergo hydrolysis to an appreciable extent because of its single positive charge and large ionic radius, which yield low charge density and weak polarization of water molecules in the first solvation shell. In mixed solvent systems or in the presence of strongly coordinating ligands, \(\mathrm{Rb}^+\) can form coordination complexes, but these are typically labile and dominated by electrostatic interactions.
Reactivity and Stability
The rubidium cation is chemically stable in common aqueous and solid matrices. It forms ionic crystals with typical counterions; these salts are generally stable to air and moisture under normal handling conditions. The cation can participate in ion‑exchange equilibria, be sequestered by macrocyclic ligands (e.g., crown ethers and cryptands) that are size‑selective for larger alkali ions, and be exchanged on inorganic ion‑exchange media. Redox chemistry is not relevant to \(\mathrm{Rb}^+\) (reduction to the metal requires strongly reducing conditions and pertains to the elemental form rather than the cation). Thermal, photochemical, or oxidative instability of \(\mathrm{Rb}^+\) salts is governed primarily by the properties of the counterion and the solid‑state lattice rather than the cation itself.
Molecular and Ionic Parameters
Formula and Molecular Weight
- Formula: \(\mathrm{Rb}^+\)
- Molecular weight (nominal): \(85.468\,\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact / monoisotopic mass: \(84.91178974\) (atomic mass units)
Additional computed descriptors: topological polar surface area \(=0\); formal charge \(=+1\); heavy atom count \(=1\).
Constituent Ions
The primary ionic species is the rubidium cation, \(\mathrm{Rb}^+\). In practice \(\mathrm{Rb}^+\) is encountered paired with a wide variety of anions (common examples in industrial and laboratory contexts include chloride, nitrate, sulfate, and halide or oxyanion counterions). Ion pairing, lattice packing and solvation shell structure determine the macroscopic properties (solubility, melting point, conductivity) of the resulting salts.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS RN: 22537-38-8
- InChI: InChI=1S/Rb/q+1
- InChIKey: NCCSSGKUIKYAJD-UHFFFAOYSA-N
- SMILES: [Rb+]
- UNII: PR87B22TGJ
- ChEBI: CHEBI:49847
- DTXSID: DTXSID50177059
- HMDB: HMDB0001327
- KEGG: C17061
- Wikidata: Q27104730
Synonyms and Common Names
Depositor-supplied synonyms and common names include: - rubidium cation - RUBIDIUM ION - rubidium(1+) - Rubidium, ion (Rb1+) - UNII-PR87B22TGJ - PR87B22TGJ - rubidium(I) cation - rubidium(1+) ion - RUBIDIUM ION(1+) - CHEBI:49847 - DTXSID50177059 - RefChem:180179 - DTXCID2099550 - 22537-38-8 - Rb+ - rubidium(I) - Rubidium + - Rubidium (I) ion - Rubidium [UN1423] - Rb(+) - SCHEMBL29494657 - C17061 - Q27104730
Industrial and Commercial Applications
Functional Roles and Use Sectors
Rubidium in its ionic form is primarily used where the chemical or physical properties of a large alkali cation are required. Commercial and technical roles for rubidium salts and solutions include use as doping agents in specialty glass formulations, components in certain electronic and optical materials, reagents in chemical synthesis and analytical chemistry, and as a research reagent in fundamental studies of ion transport and ion coordination. Isotopically specific forms of rubidium (e.g., radioactive isotopes) have applications in nuclear medicine and tracer studies; such applications concern the isotope and its radiochemical handling rather than any unique chemical reactivity of the nonradioactive cation.
Typical Application Examples
- Laboratory reagent for studies of alkali metal ion effects and ion‑exchange experiments.
- Dopant or modifier in specialty glass and ceramic formulations to tailor refractive index or other properties.
- Source of rubidium ions for electrochemical and conductivity reference experiments.
- Component of standardized solutions and calibration materials in analytical protocols (chosen for ionic size and behavior similar to potassium in certain contexts).
If a specific concise application summary is required for procurement or formulation decisions, selection should be informed by the intended counterion, purity grade, and isotopic composition.
Safety and Handling Overview
Health and Environmental Hazards
Rubidium salts are generally of low acute chemical toxicity compared with many transition‑metal salts, but, as with other soluble alkali salts, excessive exposure may disturb electrolyte balance if significant amounts are absorbed. As a biologically active alkali cation, rubidium can substitute partially for potassium in some biological systems; chronic or high‑dose exposure should be avoided. Environmental fate is dominated by solubility and mobility in aqueous media; soluble rubidium compounds can be mobile in soil and water and should be managed to minimize uncontrolled release.
Storage and Handling Considerations
Handle rubidium salts using standard industrial chemical hygiene measures: avoid inhalation of dust, prevent contact with skin and eyes, use appropriate gloves and eye protection, and provide local exhaust for dust‑generating operations. Store in tightly closed containers in a cool, dry, well‑ventilated area away from incompatible materials (evaluate compatibility with strong complexing agents and reactive metals). Rubidium metal (elemental form) is highly reactive and requires specialized storage and handling; this does not apply to the typical ionic salts discussed here. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
