This bar chart displays the number of valence electrons for elements across the periodic table. Valence electrons are those in the outermost shell, determining chemical reactivity.

The periodic pattern is clear: elements in the same group share the same valence electron count. Alkali metals have 1, halogens have 7, and noble gases have 8 (except helium with 2). Understanding valence electrons predicts oxidation states, bonding behavior, and explains why elements in the same column show similar chemical properties.