Science, Tech, Math › Science Oxidation Number Definition Chemistry Glossary Definition of Oxidation Number Share Flipboard Email Print The transition metals have multiple oxidation numbers, which are why they form so many colors of solutions. Ben Mills 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 July 03, 2019 Oxidation Number Definition:atomcoordination compoundligandsthe oxidation numberoxidation state The oxidation number is represented by a Roman numeral. The plus sign is omitted for positive oxidation numbers. The oxidation number is seen as a superscript to the right of an element symbol (e.g., FeIII) or in parentheses after the element name [e.g., Fe(III)] usually with no space between the element name and the parentheses.