- s orbital → round (sphere), holds 2 electrons.
- p orbitals → dumbbell-shaped, 3 types (px, py, pz), together hold 6 electrons.
- d orbitals → cloverleaf shapes, 5 types, together hold 10 electrons.
- f orbitals → very complex shapes, 7 types, together hold 14 electrons.
So, s is simplest, f is the most complex.