Although electrons 'orbit' the nucleus, and they exist in defined electron levels, they do not orbit in the typical sense i.e. they do not travel around distinct spherical paths or shells as in the depiction below. Why say that they do then? Because this model is a lot easier to understand when you're first learning about electron configurations.
Instead, within these 'shells' exists smaller shells which we call sub-orbitals. The first of these sub-orbitals are named s-orbitals, p-orbitals and d-orbitals.
Electron Sub-Orbital Shapes
As you can see below, each type of orbital varies in shape. The s-orbitals are spherical, but the others can get very complicated. You can click on the images or text below to learn more about each type of sub-orbital, including the number of electrons they hold.
Number and Type of Sub-orbitals in Each Shell
Not every shell has s-orbitals, p-orbital and d-orbitals. Instead it varies depending on the shell; the further away it is from the nucleus of the atom, the more sub-orbitals it has.
- n=1 has only one s-orbital
- n=2 has an s-orbital, and a set of p-orbitals
- n=3 has an s-orbital, a set of p-orbitals and a set of d-orbitals.
- n=4 has an s-orbital, a set of p-orbitals, a set of d-orbitals and a set of f-orbitals.
One of the best ways to remember what sub-orbitals each shell contains is to remember this little picture.
The shell numbers are written in a vertical column (in red above), and the different sub-orbitals they contain are written horizontally along the same row, to the right (in black above). As you can see, there is a little pattern to it - which makes it easier to remember.