D. I. MENDELEEV'Sˈ PERIODIC TABLE OF CHEMICAL ELEMENTS. YESTERDAY. TODAY. TOMORROW
D.I. Mendeleev went down in the history of global science as the discoverer of the periodic law and the author of the periodic table of chemical elements, based on that law. On March 1, 1869 he published the periodic law and its consequence, i. e., a table composed of the rows containing the vertically located symbols of 67 elements known at that time. Inert gases had not been discovered yet, and no information had existed regarding atom structures. Vertically located symbols of elements became a preimage of the table periods with their horizontal arrangement. In subsequent decades, Mendeleev completed the table with newly discovered elements, including those he had predicted, i. e., the “stretchers” of the periodic law - Ga, Ge, and Sc. Mendeleev assumed that the properties of elements were similar for every eight positions, which number corresponded with the maximum possible valency, or acidity, of the elements in at least binary compounds. For this reason, many scientists remain committed to the number of 8 today (VIII is the ordinal number of the largest group). The group size has erroneously and forcedly become unnaturally cumbersome due to the fault of its systemizers (not the author of the periodic law, but the chemists of next generations). When reasoned, the table consisting of 8 groups did not consider the natural sequential arrangement of the elements in the table according to their ordinal (atomic) numbers. This resulted in creating an artificial agglomerate containing, as of today, three speculative families of totally 12 d-elements, and a group of six inert gases. In 1989, IUPAC recommended/approved the table version consisting of 18 groups. The long overdue legalization of the table was immediately accepted by foreign countries, including Russia’s nearest neighbors, such as Belarus, Poland, etc. The authors of this paper were the first to follow the IUPAC’s resolution in Russia. We have created a bilingual (Russian-English) table with as informative contents for each element as possible and published it in our large-edition monographs and in many educational journals. The table of 18 groups is optimal for chemical education. It was used in many learning guides earlier, well in advance of the IUPAC’s resolution; however, there was a difference in it - the groups were numbered using Roman numerals. Previously, the longest table version was known, consisting of 32 groups and including both lanthanides and actinides with their sequential arrangement within the table according to their original numbers. Since 2016, the discovery of element 118 (an extremely short-living inert gas, oganesson, Og) the seventh period of the table has been completed. Subsequent elements being synthesized and also short-living will take their places in the first groups of the eighth period of the table.