Science, Tech, Math › Science Spin Quantum Number Definition Chemistry Glossary Definition of Spin Quantum Number Share Flipboard Email Print The spin quantum number describes the shape and energy of electron orbitals. RICHARD KAIL / 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 December 07, 2018 The spin quantum number is the fourth quantum number, denoted by s or ms. The spin quantum number indicates the orientation of the intrinsic angular momentum of an electron in an atom. It describes the quantum state of an electron, including its energy, orbital shape, and orbital orientation. The only possible values of a spin quantum number are +½ or -½ (sometimes referred to as 'spin up' and 'spin down'). The value of spin is a quantum state, not something so easily understood as the direction in which an electron spins! Sources Atkins, P.; de Paula, J. (2006). Physical Chemistry (8th ed.). W. H. Freeman. ISBN 0-7167-8759-8.Bertolotti, Mario (2004). The History of the Laser. CRC Press. pp. 150–153.Merzbacher, E. (1998). Quantum Mechanics (3rd ed.). John Wiley. p.430-1 ISBN 0-471-88702-1.