This line chart tracks the electron shell filling pattern across all elements. Each line represents one of the seven principal energy levels (shells) and how many electrons occupy it.

The chart reveals the aufbau principle in action - electrons fill lower energy orbitals first, but the pattern is complex due to orbital energy crossings. Notice how the 3d orbitals fill after 4s, and 4f after 6s. Transition metals show the d-orbital filling, while lanthanides and actinides demonstrate f-orbital filling.