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Polyatomic Ion

Polyatomic ion: charged species of ≥2 atoms; e.g., SO₄²⁻, NH₄⁺, CO₃²⁻
Quick Reference
Formula / NotationPolyatomic ion: charged species of ≥2 atoms; e.g., SO₄²⁻, NH₄⁺, CO₃²⁻
Also Known AsPolyatomic ion, compound ion, molecular ion (solid-state), radical ion

What is Polyatomic Ion?

An ion consisting of two or more atoms covalently bonded together and carrying a net electric charge. Common examples include hydroxide (OH⁻), sulfate (SO₄²⁻), nitrate (NO₃⁻), and ammonium (NH₄⁺). Polyatomic ions behave as single units in ionic compounds.

Formula & Notation

Polyatomic ion: charged species of ≥2 atoms; e.g., SO₄²⁻, NH₄⁺, CO₃²⁻

Other Names / Synonyms: Polyatomic ion, compound ion, molecular ion (solid-state), radical ion

Properties & Characteristics

A polyatomic ion is a charged chemical species composed of two or more atoms covalently bonded together, carrying an overall ionic charge. Common polyatomic anions: hydroxide (OH⁻), sulfate (SO₄²⁻), nitrate (NO₃⁻), carbonate (CO₃²⁻), phosphate (PO₄³⁻), acetate (CH₃COO⁻). Common polyatomic cations: ammonium (NH₄⁺), hydronium (H₃O⁺), mercury(I) (Hg₂²⁺). Polyatomic ions behave as a unit in ionic compounds and chemical reactions.

Uses & Applications

Polyatomic ions are fundamental in inorganic nomenclature, in ionic compound formulae, in acid-base chemistry (polyprotic acids give polyatomic conjugate bases), in biochemistry (phosphate groups in ATP and DNA, acetyl groups in acetyl-CoA), and in analytical chemistry (gravimetric and titrimetric determinations of specific polyatomic ions).

Safety Information

Toxicity of polyatomic ions varies: cyanide (CN⁻) is acutely lethal, chromate (CrO₄²⁻) is carcinogenic, azide (N₃⁻) is acutely toxic and explosive in the acid form (HN₃). Polyatomic anions of strong acids (ClO₄⁻, NO₃⁻) are oxidising agents that can ignite organic material. Always identify the specific polyatomic ion, not just the cation.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Polyatomic Ion
Formula Polyatomic ion: charged species of ≥2 atoms; e.g., SO₄²⁻, NH₄⁺, CO₃²⁻
Synonyms Polyatomic ion, compound ion, molecular ion (solid-state), radical ion

Frequently Asked Questions

An ion consisting of two or more atoms covalently bonded together and carrying a net electric charge. Common examples include hydroxide (OH⁻), sulfate (SO₄²⁻), nitrate (NO₃⁻), and ammonium (NH₄⁺). Polyatomic ions behave as single units in ionic compounds.

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