Science, Tech, Math › Science Polyatomic Ion: Definition and Examples What Is a Polyatomic Ion in Chemistry? Share Flipboard Email Print This is the chemical structure of the pyrophosphate anion, an example of a polyatomic ion. Todd Helmenstine Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College 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. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. 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.