The United Nations General Assembly has proclaimed 2019 the International Year of the Periodic Table of Chemical Elements in honor of the 150th anniversary of its creation.
On 1 March 1869, Russian scientist Dmitry Mendeleev drew up a table An Experiment on a System of Elements Based on Their Atomic Weights and Chemical Similarities. The idea was that with the grow of atomic weights of the elements, their chemical properties change periodically, not monotonically. For instance, sodium resembles potassium, fluorine resembles chlorine, and gold resembles silver and copper. Mendeleev created several variants of his periodic table and used it to correct the atomic weights of some already discovered elements, to predict the properties of the elements yet to be discovered (gallium, germanium and scandium), and also left spaces, where new elements had to be placed.
The Periodic Table was pivotal for the development of knowledge of atoms and molecules. Thanks to it, the modern concept of a chemical element was formed, and the understanding of elements and compounds was ascertained.
The composition of the souvenir pack in cover “International Year of the Periodic Table of Chemical Elements” includes a postal block №2455 “International Year of the Periodic Table of the Elements” with an overprint.
Edition: 4000 pcs.