Beginner Topic 721 of 1102 Inorganic Chemistry
Polyatomic Ions
Charged groups of covalently bonded atoms such as sulfate, nitrate and ammonium.
In-depth explanation of Polyatomic Ions
Polyatomic ions are charged groups of covalently bonded atoms that behave as a single unit in reactions. Common examples include ammonium, NH4+, nitrate, NO3-, sulfate, SO4 2-, carbonate, CO3 2-, phosphate, PO4 3-, and dichromate, Cr2O7 2-. When a formula contains more than one polyatomic ion, brackets are used, as in Ca3(PO4)2. Their charges must be memorized, since they determine the formulas of the compounds they form. Nitrate and ammonium salts are generally soluble.
Going deeper: Polyatomic Ions
Key ideas: Memorize the common ones: NH4+, OH-, NO3-, NO2-, CO3 2-, HCO3-, SO4 2-, SO3 2-, PO4 3-, ClO4-, ClO3-, ClO2-, ClO-, CN-, C2H3O2- (acetate), MnO4-, CrO4 2-, Cr2O7 2-, SCN-, C2O4 2-, O2 2- (peroxide). Series with chlorine show -ate means one oxygen more than -ite. Hydrogen additions reduce charge by one: HSO4- is hydrogen sulfate. Parentheses mark more than one polyatomic unit: Ca3(PO4)2.
Common mistakes and connections: Students confuse sulfate and sulfite, nitrate and nitrite, and also mis-assign charge on phosphate and ammonium. Peroxide O2 2- is not oxide. The formulas keep ion identity in solution, so do not split them in net ionic equations. Links to nomenclature, solubility rules, acid-base and net ionic equations.
Visualization of Polyatomic Ions
The ammonium ion NH4+ is a tetrahedral polyatomic cation with a covalently bonded group that carries an overall charge. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Calcium phosphate is written Ca3(PO4)2 because two phosphate ions, each with charge -3, balance three calcium ions, each with charge +2.
Frequently asked questions about Polyatomic Ions
What is Polyatomic Ions?
Charged groups of covalently bonded atoms such as sulfate, nitrate and ammonium.
Is Polyatomic Ions a beginner, intermediate or advanced topic?
Polyatomic Ions is a beginner topic in Inorganic Chemistry. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Polyatomic Ions?
Study these earlier topics in Inorganic Chemistry first: Photovoltaic Materials, Water Treatment, Inorganic Nomenclature.
What comes after Polyatomic Ions?
The next topics in Inorganic Chemistry are Chemical Formula Types and Hydrates.
Can I practise Polyatomic Ions with quizzes?
Yes. The interactive lesson includes a self-check question on Polyatomic Ions, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Polyatomic Ions fits in Inorganic Chemistry
Polyatomic Ions is topic 106 of 113 in Inorganic Chemistry.