BackCommon Polyatomic Ions and Their Formulas
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Polyatomic Ions
Introduction to Polyatomic Ions
Polyatomic ions are ions composed of two or more atoms covalently bonded, that together carry a net electrical charge. These ions are fundamental in general chemistry, especially in naming compounds, writing chemical formulas, and understanding chemical reactions.
Definition: A polyatomic ion is a charged species (ion) consisting of two or more atoms bonded together, acting as a single unit.
Importance: Polyatomic ions are commonly found in ionic compounds and play key roles in acid-base chemistry, precipitation reactions, and redox processes.
Notation: The charge on a polyatomic ion is shown as a superscript (e.g., SO42− for sulfate).
Common Polyatomic Ions
The following table lists some of the most frequently encountered polyatomic ions in general chemistry, along with their chemical formulas and charges.
Name | Formula | Charge |
|---|---|---|
Acetate | C2H3O2− | -1 |
Carbonate | CO32− | -2 |
Bicarbonate (Hydrogen carbonate) | HCO3− | -1 |
Hydroxide | OH− | -1 |
Nitrate | NO3− | -1 |
Nitrite | NO2− | -1 |
Chromate | CrO42− | -2 |
Dichromate | Cr2O72− | -2 |
Phosphate | PO43− | -3 |
Ammonium | NH4+ | +1 |
Hypochlorite | ClO− | -1 |
Chlorite | ClO2− | -1 |
Chlorate | ClO3− | -1 |
Perchlorate | ClO4− | -1 |
Permanganate | MnO4− | -1 |
Sulfate | SO42− | -2 |
Sulfite | SO32− | -2 |
Cyanide | CN− | -1 |
Thiosulfate | S2O32− | -2 |
Mercury (I) | Hg22+ | +2 |
Mercury (II) | Hg2+ | +2 |
Naming Compounds with Polyatomic Ions
When naming ionic compounds containing polyatomic ions, the name of the cation is given first, followed by the name of the polyatomic anion. If more than one polyatomic ion is needed to balance the charge, parentheses are used around the ion's formula.
Example: Calcium nitrate:
Example: Ammonium sulfate:
Patterns in Polyatomic Ions
Many polyatomic ions with the same central atom differ by the number of oxygen atoms and their prefixes/suffixes (e.g., chlorate, chlorite, perchlorate, hypochlorite).
"-ate" ions have more oxygen atoms than "-ite" ions (e.g., sulfate SO42− vs. sulfite SO32−).
Prefixes "per-" and "hypo-" indicate more or fewer oxygen atoms, respectively.
Practice and Application
Memorizing common polyatomic ions is essential for success in general chemistry.
They are used in writing chemical equations, predicting products, and balancing charges in compounds.
Additional info: Polyatomic ions are introduced in general chemistry courses under topics such as "Molecules and Compounds" and "Chemical Nomenclature." Understanding their structure and naming conventions is foundational for later topics such as acid-base chemistry, solubility, and redox reactions.
