The Periodic Law establishes that elemental properties function as a periodic variable dependent on atomic number rather than atomic mass, organizing elements into vertical groups sharing similar valence configurations and horizontal periods defined by increasing proton count. This classification partitions chemical substances into distinct domains of metals, metalloids, nonmetals, noble gases, transition metals, and inner transition series based on electronic structure boundaries. The framework explains periodic trends in physical attributes such as atomic radius and metallic character through systematic variations across the table's structural dimensions.
Prerequisite chain context: requires Major Divisions of the Periodic Table in Chemistry.