Atoms are built with layers of electrons called principal shells. You can think of these main shells like the floors of a parking garage. Inside each floor, there are different parking sections with specific shapes.
These sections are the subshells. We label these subshells with the letters s, p, d, and f. The letters describe the physical shape of the electron clouds.
An s subshell looks like a hollow sphere. A p subshell looks like a pinched dumbbell. The d and f subshells have much more complex flower shapes.
Each shape determines how atoms can bond with one another. We find the number of a subshell using the azimuthal quantum number. This mathematical rule dictates exactly how many subshells fit on each main level.
A common student mistake is confusing a subshell with an orbital. A subshell is a collection of orbitals that share the same energy level and shape. Each individual orbital inside the subshell can only hold two electrons.
The total capacity of a subshell depends on its shape. An s subshell holds two electrons. A p subshell holds six electrons.
A d subshell holds ten electrons. An f subshell holds fourteen electrons.