Science, Tech, Math › Science Molecular Orbital Definition Share Flipboard Email Print A molecular orbital is a mathematical function that describes an electron in a molecule. Adisonpk, Getty Images 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 10, 2019 A molecular orbital is an orbital or wave function of a molecule's electron. The function may be used to calculate the probability of finding an electron within a specified space or to predict the molecule's chemical and physical properties. Robert Mulliken introduced the term "orbital" in 1932 to describe a one-electron orbital wave function. Electrons around a molecule can be associated with more than one atom and are often expressed as a combination of atomic orbitals. Atomic orbitals within a molecule can interact if they have compatible symmetries. The number of molecular orbitals is equal to the number of atomic orbitals combined to form a molecule.