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. Updated March 06, 2017 Polyatomic Ion Definition A polyatomic ion is an ion comprised of two or more atoms. Examples: The hydroxide cation (OH-) and the phosphate cation (PO43-) are both polyatomic ions. Continue Reading