The subshells are named SPDF because these letters originated as descriptors of spectral lines observed in alkali metals.
Origin of SPDF Notation
The letters s, p, d, and f, which designate the subshells (and corresponding atomic orbitals), don't come from arbitrary choices. Instead, they have historical roots in spectroscopy. When scientists studied the light emitted by excited atoms, they noticed distinct patterns of lines in the spectra. These lines were categorized based on their appearance.
Spectroscopic Origins
- s - Sharp: Lines described as "sharp" in their appearance.
- p - Principal: Lines described as "principal" in their appearance.
- d - Diffuse: Lines described as "diffuse" in their appearance.
- f - Fundamental: Lines described as "fundamental" in their appearance.
According to the reference, the orbital names s, p, d, and f stand for names given to groups of lines originally noted in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental.
Summary Table
| Subshell | Origin | Description |
|---|---|---|
| s | Sharp | Related to sharp spectral lines |
| p | Principal | Related to principal spectral lines |
| d | Diffuse | Related to diffuse spectral lines |
| f | Fundamental | Related to fundamental spectral lines |
These initial letters were then adopted to label the atomic orbitals corresponding to those spectral transitions. Higher angular momentum orbitals follow alphabetically (g, h, i, k, etc.), but these are rarely encountered in most chemical contexts.
