This Day in World History
March 6, 1869
Mendeleev’s Periodic Table presented in publicOn March 6, 1869, Dmitri Mendeleev’s breakthrough discovery was presented to the Russian Chemical Society. The chemist had determined that the known elements — 70 at the time — could be arranged by their atomic weights into a table that revealed that their physical properties followed regular patterns. He had invented the periodic table of elements.
In his early twenties, Mendeleev had intuited that the elements followed some kind of order, and he spent thirteen years trying to discover it. In developing his system, he drew on the data and ideas of scientists around the world. Two — Lothar Meyer and British chemist John Alexander Reina Newlands — had published ideas about the periodicity of elements. But Mendeleev’s addressed every known element, which theirs had not.
His system also surpassed the others because he accounted for gaps in the sequence of elements. Mendeleev said that an element would be discovered to fill each gap and even predicted the properties of those elements. The discovery of the one of these missing elements — gallium, in 1875 — helped spur wide acceptance of Mendeleev’s system.
Later work showed that Mendeleev’s reliance on atomic weight to determine periodicity is not completely correct. While atomic weight tends to increase as one moves from element to element, there are exceptions. Mendeleev also did not have the theoretical understanding to explain why the elements exhibited these periodic characteristics. Nevertheless, his achievement marked an important milestone in the understanding of the physical world.
Mendeleev did not personally present his breakthrough to the Chemical Society. Ill on the day of the meeting, he asked a colleague to deliver the report.
Interestingly, the date celebrated for this event reflects Russia’s use of the “Old Style” Julian calendar. According to the “New Style” Gregorian calendar — not adopted in Russia until after 1918 — Mendeleev’s periodic table was presented twelve days later, on March 18.