What do the letters s, p, d, and f in the orbital names stand for?


Vocabulary
angular momentum quantum number*
line spectrum*
orbital*
spectroscopy*
You might expect that the 's' stands for 'spherical' and 'p' stands for 'polar' because these imply the shapes of the s and p orbitals, but unfortunately, the letter designations have nothing to do with the orbital shapes.

Spectroscopists associated transitions involving energy levels with different ell values with different groups of lines in the line spectra of the alkali metals. The line groups were called sharp, principal, diffuse, and fundamental. When the angular momentum quantum number was used to describe and explain these groups of lines, s became an abbreviation for ell = 0, p meant ell = 1, d meant ell = 2, and f meant ell = 3. For consistency, higher values of the angular momentum quantum numbers are designated alphabetically (g means ell = 4, h means ell = 5, and so on).

Author: Fred Senese senese@antoine.frostburg.edu



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