actinide series a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series. The series always includes the 14 elements with atomic numbers 90 through 103. The other members are (in order of increasing atomic number) thorium , protactinium , uranium , neptunium , plutonium , americium , curium , berkelium , californium , einsteinium , fermium , mendelevium , nobelium , and lawrencium . Thorium and uranium... Read more