This line chart tracks first ionization energy - the minimum energy needed to remove the outermost electron - across all elements. Clear periodic peaks and valleys appear.

The peaks occur at noble gases, whose complete electron shells strongly resist ionization. Valleys appear at alkali metals, which easily lose their single valence electron. The sawtooth pattern within each period reflects subshell effects: slight drops occur when filling p-orbitals begins and when p-orbitals become half-filled.