Editing Azimuthal quantum number (section)

== Nomenclature ==
The term "azimuthal quantum number" was introduced by [[Arnold Sommerfeld]] in 1915<ref>{{Cite book |last=Whittaker |first=Edmund Taylor |title=A history of the theories of aether and electricity |date=1989 |publisher=Dover |isbn=978-0-486-26126-3 |series=Dover classics of science and mathematics |location=New York}}</ref>{{rp|II:132}} as part of an ad hoc description of the energy structure of atomic spectra. Only later with the quantum model of the atom was it understood that this number, {{mvar|ℓ}}, arises from quantization of orbital angular momentum. Some textbooks<ref name=Schiff>{{Cite book |last=Schiff |first= Leonard  |title=Quantum mechanics |publisher= McGraw-Hill |year= 1949}}</ref>{{rp|199}} and the ISO standard 80000-10:2019<ref name="iso">{{Cite web |title=ISO Online Browsing Platform |url=https://www.iso.org/obp/ui/en/#iso:std:iso:80000:-10:ed-2:v1:en |access-date=2024-02-20 |at=10-13.3}}</ref> call {{mvar|ℓ}} the '''orbital angular momentum quantum number'''.

The energy levels of an atom in an external magnetic field depend upon the {{mvar|''m''{{sub|ℓ}}}} value so it is sometimes called the  magnetic quantum number.<ref>{{Cite book |last=Eisberg |first=Robert M. |title=Quantum physics of atoms, molecules, solids, nuclei, and particles |last2=Resnick |first2=Robert |date=2009 |publisher=Wiley |isbn=978-0-471-87373-0 |edition=2. ed., 37. [Nachdr.] |location=New York}}</ref>{{rp|240}}

The lowercase letter {{mvar|ℓ}}, is used to denote the orbital angular momentum of a single particle. For a system with multiple particles, the capital letter {{mvar|L}} is used.<ref name="iso"/>