Mendeleev Publishes the Periodic Table of Elements

Dmitri Mendeleev presented his periodic table to the Russian Chemical Society on March 6, 1869, arranging the 63 known elements by atomic weight and recurring chemical properties. His table predicted the existence and properties of undiscovered elements — including gallium, scandium, and germanium — all subsequently confirmed. Lothar Meyer independently developed a similar arrangement the same year. The periodic table provided the first systematic organizational framework for all matter, transforming chemistry from an empirical catalog into a predictive science, and remains the foundational reference structure of the discipline.