I know there are orbitals named S, P, D and F.

  1. But why they named like that. is there any significance for the letter?
  2. Is there any order in filling the orbitals?
  • $\begingroup$ In my old memory they were ; Sharp , Pronounced, Diffuse, and Foggy based on the film images. $\endgroup$ May 4, 2018 at 14:53

1 Answer 1


From the abstract of Structure of the Line Spectra of the Elements as published in the 1890 Journal of the Chemical Society.

There are three kinds of series — principal, sharp (well-defined), and diffuse (ill- defined). The principal series form the most vivid lines in the spectra, and only occur in the first, periodic group ; next come the diffuse (really double) lines ...

See also On the Structure of the Line Spectra of the Chemical Elements, also from 1890 by Rydberg:

Liveing and Dewar were the first to remark the existence of the series, as well as their different appearances. They are of three kinds : diffuse, sharp, and principal series. The first two are formed by the above-mentioned doublets or triplets ...

Later, "fundamental" was added.

For more information see The Origin of the s, p, d, f Orbital Labels J. Chem. Educ., 2007, 84, 757-758

  • 1
    $\begingroup$ Can you please add an image of how the different spectra actually look like? $\endgroup$
    – Shub
    May 23, 2021 at 15:59

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