Periodic table of chemical elements or, as it is called, the periodic table, which made it possible to classify chemical elements, depending on their properties and the charge of the atomic nucleus was discovered by Russian scientist-chemist D. I. Mendeleev in 1869. According to legend, the system of chemical elements came to Mendeleev in a dream, but the author himself said that he spent 20 years looking for a solution.
The discovery of the periodic table was facilitated by Mendeleev's love of solitaire unfolding. The scientist pointed out the atomic weights of certain elements on playing cards, and then laid them out as if he was playing a card game. Initially, it consisted of 56 elements, however, with the development of fundamental and applied science (including nuclear fusion) in the XX century, the number of elements discovered at the moment reached 118. The 113th, 115th, 117th, and 118th elements were declared by IUPAC (international Union of theoretical and applied chemistry) most recently, on December 30, 2015. There are 26 letters in the Latin alphabet, and almost all of them are used to name elements in the periodic table. Except for one "J". In total, over the past 50 years, D. I. Mendeleev's Periodic table has been replenished with 17 new elements (from 102 to 118), 9 of which were synthesized at the Joint Institute for nuclear research in Dubna near Moscow. Most isotopes of superheavy elements (elements with a sequence number >100) are unstable and undergo decay for a very short period of time. Thus, the recently discovered ununpentium, also known as element 115 and Eka-bismuth, has a half-life of only about 220 milliseconds. One important feature that makes the periodic table an outstanding discovery is its predictive power. The table at the time of its appearance left empty cells for elements that, according to the assumptions of Mendeleev, should exist, but have not yet been opened. For example, the properties of gallium, scandium and magnesium Mendeleev described even before their discovery. If we take the modern periodic table, cut out of its middle columns and put them in half in groups of 4 elements, the groups that will touch ("kiss"), in the chemical sense can" love each other", that is, interact. The elements of these groups will have complementary (i.e. complementary) structures, which makes possible reactions between them. The largest periodic table was installed on the walls of the faculty of chemistry at the University of Murcia in Spain. In total, the installation occupies a total of about 150 m2 and consists of 118 metal squares 75×75 cm in size.
