Science, Tech, Math › Science Hydroxyl Group Definition in Chemistry Share Flipboard Email Print The hydroxyl functional group is an oxygen-containing group based on an alcohol or OH group. Ben Mills Science Chemistry Basics Chemical Laws 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 November 05, 2018 The hydroxyl group is a functional group consisting of a hydrogen atom covalently bonded to an oxygen atom. The hydroxyl group is denoted by -OH in chemical structures and has a valence charge of -1. The hydroxyl radical is very reactive, so it quickly reacts with other chemical species. Hydroxyl radicals can cause DNA and cell damage. Hydroxyl Versus Hydroxy The terms "hydroxyl" and "hydroxy" tend to be used interchangeably, but they don't technically mean the same thing. The term hydroxyl means the radical OH. The functional group -OH is more properly called a hydroxy group. Further, the [OH-] anion, which is called hydroxide, consists of a hydroxy group.