Starting in 2020, scientists will attempt to synthesize elements 119 and 120, with a newly inaugurated Superheavy Element Factory and an experimental apparatus that is 100 times more sensitive. They hope to reach the “island of stability,” a fabled region of the periodic table populated by superheavy elements with greater longevity.

Like Pandora’s box, the discovery of superheavy elements presents tricky questions, Dr. Oganessian said. Will these elements behave the way the periodic table predicts? So far, only some deviations in behavior are expected. But as the atomic numbers go up, deviations will increase rapidly, challenging the periodic table’s schematic integrity.

Will the periodic table hold up? Or as Pekka Pyykkö, a computational chemist at the University of Helsinki, put it in the title of a 2016 paper: “Is the Periodic Table All Right (‘PT OK’)?” Probably, with modifications, he concluded. Dr. Pyykkö formulated a periodic table that chemically classifies the elements up to atomic number 172.