CHAPTER THIRTEEN FERMIUM, MENDELEVIUM, NOBELIUM, AND

Chemistry (IUPAC) recently reviewed the names of all the trans‐fermium ele-ments; Münzenberg (1999) has published a detailed discussion of the problems and the resolution. First, a Transfermium Working Group decided the priority of discoveries. Next, the discoverers proposed names to the IUPAC and names were officially accepted by that body. The names for the elements mendelevium, nobelium, and lawrencium were retained as originally proposed at the time of their discoveries. As of this writing, the number of known isotopes of Fm, Md, No, and Lr is 58, ranging in half‐life from as short as 0.25 ms for 250No to as long as 100.5 days for 257Fm. Relativistic effects have been predicted to affect ground state electronic configurations, ionic radii, and oxidation state for the heavier acti-nides. While the 3þ oxidation state remains a dominant feature of the heavier actinides, a tendency toward the formation of lower oxidation states has emerged. Divalency had been observed in solution for fermium through nobeli-um, in fact, the elements Fm,Md, and No are divalent in the metallic state. Due to increased 5f electron binding of the filled 5f14 shell, the 2þ oxidation state is the most stable in aqueous solution for nobelium. However, lawrencium, the last member of the actinide series, returns to the 3þ oxidation state as the most stable in aqueous solution, as predicted (Seaborg, 1949)