Ilya Abramovich Leenson - Candidate of Chemical Sciences, Senior Researcher, Faculty of Chemistry, Moscow State University, Associate Professor of the Higher College of Chemistry of the Russian Academy of Sciences, author of scientific and popular science articles, books and textbooks. The classic guide to the periodic table, which has survived several reprints, has been expanded and contains more complete information about each chemical element. The publication is supplemented with a chronological table containing background information on the history of chemistry.