Dmitri Mendeleev presents on 6 March 1869 to the Russian Chemical Society his periodic table, ordering the 63 elements then known by increasing atomic mass and grouping them by similar chemical properties into periods and groups. Mendeleev's most extraordinary contribution was not ordering the known elements but predicting the existence and properties of three then-unknown elements — eka-boron (gallium), eka-aluminium (scandium), and eka-silicon (germanium) — which were discovered in the following years with exactly the properties he had predicted. Lothar Meyer (Germany) independently developed a similar table in 1870, but priority — and above all the predictive capacity — belong to Mendeleev. The periodic table is the fundamental map of matter.