Dmitri Mendeleev published his first periodic table in 1869. On March 6, 1869, he presented his system to the Russian Chemical Society, arranging the known elements largely by atomic weight and grouping those with recurring chemical properties.
Mendeleev's table was more than a catalog. He deliberately left gaps where he believed undiscovered elements belonged and predicted several of their properties. Later discoveries of gallium, scandium, and germanium closely matched his forecasts, helping persuade chemists that periodic patterns reflected a genuine law of nature.
Other scientists had proposed earlier classifications. Johann Döbereiner described related groups called triads, John Newlands proposed his Law of Octaves, and Lothar Meyer independently developed a periodic arrangement. Mendeleev's system became especially influential because he defended it vigorously, corrected questionable atomic weights, and used it to make successful predictions.
The 1869 table was not identical to the modern periodic table. Mendeleev ordered elements by atomic weight because the structure of the atom was not yet understood. The modern table uses atomic number, a principle established after Henry Moseley's work in the early twentieth century. Mendeleev continued revising his system, including important versions published in 1870 and 1871.