History of the periodic table managed to get thallium, lead, mercury and platinum into the right groups, which is something that Mendeleev failed to do at his first attempt. Odling failed to achieve recognition, however, since it is suspected that he, as Secretary of the Chemical Society of London, was instrumental in discrediting Newlands' earlier work on the periodic table. By 1912 almost 50 different radioactive elements had been found, too many for the periodic table. Frederick Soddy in 1913 found that although they emitted different radiation, many elements were alike in their chemical characteristics so shared the same place on the table. They became
History of the periodic table and promethium respectively. During his Manhattan Project research in 1943, Glenn T. Seaborg experienced unexpected difficulties in isolating the elements americium and curium. Seaborg wondered if these elements belonged to a different series, which would explain why their chemical properties were different from what was expected. In 1945, against the advice of colleagues, he proposed a significant change to Mendeleev's table: the actinide series. Seaborg's actinide concept of heavy element electronic structure, predicting that the actinides form a transition series analogous to the rare earth series of lanthanide elements, is now well accepted and included in the periodic table. The