3.9 Atomic Energy Diagrams
It is important to understand how with each additional electron addition made to an atom, the shells and subshells are filled, with the lowest energy orbitals filling first. Below is an atomic energy diagram showing the differences in energy levels for the different shells and subshells.
Notice that the smallest principal quantum number (1) is at the lowest energy of the diagram. As you move to higher shells (higher principal quantum numbers) the energy associated is increasing. Additionally, as the l values increase (s < p < d < f) the energies associated with each subshell is increasing. Notice that orbitals with the same principal quantum number and same l value are equivalent in energy. Another name for orbitals that are equal in energy is degenerate.