Periodic table (detailed cells)
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev invented the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
2019
2019 has been designated as International Year of the Periodic Table of Chemical Elements by the United Nations General Assembly given that it coincides with the 150th anniversary of its creation by Dmitri Mendeleev in 1869.