Polyatomic Ion: Definition and Examples

What Is a Polyatomic Ion in Chemistry?

polyatomic ion
This is the chemical structure of the pyrophosphate anion, an example of a polyatomic ion. Todd Helmenstine
by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated January 12, 2019

Polyatomic ion definition: A polyatomic ion is an ion composed of two or more atoms.

Examples: The hydroxide cation (OH-) and the phosphate cation (PO43-) are both polyatomic ions.