An electron subshell is a division of a larger electron shell with the same azimuthal quantum number based on energy levels. The number of electrons permitted in a subshell is equal to 2l + 1. Energy subshells identified by the angular momentum quantum number, . They can also be described using spectroscopic notation:
|Angular momentum quantum number||Spectroscopic notation||Spectroscopic name|
Spectroscopic notation originates from before a quantum model of the hydrogen atom, where in the spectrum of hydrogen it was noticed that the lines had different shapes. Subshells of with an angular momentum number greater than 3 are represented by the letters after f, so corresponds to the g subshell and so on.
Each subshell corresponds to a particular shape of the location in which electrons can be found, for example the s subshells take the shape of a sphere while the p subshells take the shape of a dumbbell. The number of electrons that can be held in each subshell varies, with s holding 2, p holding 6, d holding 10 and f holding 14. It can be seen that the maximum number of electrons a subshell can have is . Generally electrons around an atom are primarily divided in energy levels by shell and then subshell, although this is not always the case (for instance the 3d subshell is of a higher energy level than the 4s subshell).