Common Polyatomic Ions: Names, Formulas, and Properties

Common Polyatomic Ions

Introduction to Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded, acting as a single unit in chemical reactions. They play a crucial role in the composition of many ionic compounds and are commonly encountered in general chemistry.

• Definition: A polyatomic ion is an ion consisting of multiple atoms bonded together, carrying a net positive or negative charge.

• Importance: Polyatomic ions are found in acids, bases, salts, and many other compounds.

• Examples: Sulfate ($SO_4^{2-}$), Nitrate ($NO_3^-$), Ammonium ($NH_4^+$)

Table of Common Polyatomic Ions

The following table lists the names and formulas of some of the most frequently encountered polyatomic ions in general chemistry.

Name	Formula	Name	Formula
Acetate	$C_2H_3O_2^-$	Hypochlorite	$ClO^-$
Carbonate	$CO_3^{2-}$	Chlorite	$ClO_2^-$
Hydrogen carbonate (bicarbonate)	$HCO_3^-$	Chlorate	$ClO_3^-$
Hydroxide	$OH^-$	Perchlorate	$ClO_4^-$
Nitrate	$NO_3^-$	Permanaganate	$MnO_4^-$
Nitrite	$NO_2^-$	Sulfite	$SO_3^{2-}$
Chromate	$CrO_4^{2-}$	Hydrogen sulfite (bisulfite)	$HSO_3^-$
Dichromate	$Cr_2O_7^{2-}$	Sulfate	$SO_4^{2-}$
Phosphate	$PO_4^{3-}$	Hydrogen sulfate (bisulfate)	$HSO_4^-$
Hydrogen phosphate	$HPO_4^{2-}$	Cyanide	$CN^-$
Dihydrogen phosphate	$H_2PO_4^-$	Peroxide	$O_2^{2-}$
Ammonium	$NH_4^+$

Key Properties and Examples

• Charge: Polyatomic ions can be positively charged (cations, e.g., ammonium $NH_4^+$) or negatively charged (anions, e.g., sulfate $SO_4^{2-}$).

• Bonding: Atoms within a polyatomic ion are held together by covalent bonds, but the ion as a whole participates in ionic bonding in compounds.

• Usage in Compounds: Polyatomic ions combine with oppositely charged ions to form neutral ionic compounds. For example, sodium sulfate ($Na_2SO_4$) contains two sodium ions ($Na^+$) and one sulfate ion ($SO_4^{2-}$).

• Naming: The names of polyatomic ions often reflect their composition and oxidation state. For example, chlorate ($ClO_3^-$) and perchlorate ($ClO_4^-$) differ by one oxygen atom.

Examples of Polyatomic Ion Applications

• Acids and Bases: Many acids contain polyatomic ions, such as sulfuric acid ($H_2SO_4$) containing sulfate ($SO_4^{2-}$).

• Biological Systems: Phosphate ions ($PO_4^{3-}$) are essential in biological molecules like DNA and ATP.

• Industrial Uses: Ammonium ions ($NH_4^+$) are found in fertilizers; nitrate ($NO_3^-$) is used in explosives and fertilizers.

Summary Table Purpose

The table above serves as a reference for identifying and memorizing the most common polyatomic ions encountered in general chemistry courses. Mastery of these ions is essential for success in chemical nomenclature, formula writing, and understanding chemical reactions.