The angular momentum quantum number, ℓ, is the quantum number associated with the angular momentum of an atomic electron. The angular momentum quantum number determines the shape of the electron's orbital.

**Also Known As: **azimuthal quantum number, second quantum number

**Example: **A p orbital is associated with an angular momentum quantum number equal to 1.

### History

The angular momentum quantum number came from the Bohr model of the atom, as proposed by Arnold Sommerfeld. The lowest quantum number from spectroscopic analysis had an angular momentum quantum number of zero. The orbit was considered to be an oscillating charge, which appeared as a sphere in three dimensions.

### Source

- Eisberg, Robert (1974).
*Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles*. New York: John Wiley & Sons Inc. pp. 114–117. ISBN 978-0-471-23464-7.