Second Quantum Number Definition

The second quantum number describes the shape of an electron's orbit.
The second quantum number describes the shape of an electron's orbit. PASIEKA / Getty Images
by Anne Marie Helmenstine, Ph.D.
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.
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.