Dmitri Mendeleev

Dmitri Mendeleev created the definitive version of the Periodic Table of the Elements, one of the most iconic and predictive tools in all of science. While others noted patterns, Mendeleev's genius was in arranging elements by atomic weight and chemical properties, leaving gaps for undiscovered elements. He boldly predicted the properties of these missing elements (e.g., gallium, scandium, germanium) with remarkable accuracy. When they were discovered, his table was validated, transforming chemistry from a collection of disparate facts into a coherent, logical system. The periodic table revealed the fundamental periodicity in the properties of elements, later explained by atomic structure, and remains the central organizing principle of chemistry.