Science, Tech, Math › Science Second Quantum Number Definition Share Flipboard Email Print The second quantum number describes the shape of an electron's orbit. PASIEKA / 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 August 08, 2019 The second quantum number, ℓ, is the quantum number associated with the angular momentum of an atomic electron. The second quantum number determines the shape of the electron's orbital. When the second quantum number is combined with the principal, magnetic, and spin quantum numbers, an electron in an atom is described completely. Also Known As: azimuthal quantum number, angular momentum quantum number Examples: A p orbital is associated with a second quantum number equal to 1.