<P> Moseley's research showed that there were gaps in the periodic table at atomic numbers 43 and 61, which are now known to be occupied by technetium and promethium respectively . </P> <P> 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 . </P> <P> 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 actinide series is the second row of the f - block (5f series). In both the actinide and lanthanide series, an inner electron shell is being filled . The actinide series comprises the elements from actinium to lawrencium . Seaborg's subsequent elaborations of the actinide concept theorized a series of superheavy elements in a transactinide series comprising elements from 104 to 121 and a superactinide series of elements from 122 to 153 . </P>

Who is the scientist that arrange the elements in the periodic table and what is his basis