When Was the Periodic Table Created?

In 1869, Russian chemist Dmitri Mendeleev arranged the 63 known elements by increasing atomic weight and noticed that properties repeated periodically. He published his table on 6 March 1869, leaving gaps for elements he predicted would be discovered. Remarkably, three of his predictions — gallium (1875), scandium (1879), and germanium (1886) — were confirmed with properties matching his forecasts almost exactly. German chemist Lothar Meyer independently developed a similar table around the same time. The modern periodic table organises 118 confirmed elements by atomic number (protons) rather than weight, as proposed by Henry Moseley in 1913.