Seaborg's theoretical development of the actinide concept resulted in a redrawing of the Periodic Table of the Elements into its current configuration with the actinide series appearing below the lanthanide series.
12.
"' Protactinocene "', Pa ( C 8 H 8 ) 2, is an organoprotactinium compound composed of a protactinium atom sandwiched between two elements from the actinide series.
13.
"' Thorocene "', Th ( C 8 H 8 ) 2, is an organothorium compound composed of a thorium atom sandwiched between two elements from the actinide series.
14.
"' Plutonocene "', Pu ( C 8 H 8 ) 2, is an organoplutonium compound composed of a plutonium atom sandwiched between two elements from the actinide series.
15.
McCoy recommended Frank Spedding from Iowa State College in Ames, Iowa, as an expert on the rare earth elements, which were chemically similar to the actinide series that included uranium and plutonium.
16.
Chromium, molybdenum, tungsten, and uranium were sometimes included in this group, but they would be later rearranged as part of group VIB; uranium would later be moved to the actinide series.
17.
It was also pointed out that the actinide contraction at the end of the actinide series was larger than the analogous lanthanide contraction, with the exception of the last actinide, lawrencium : the cause was speculated to be relativistic effects.
18.
In addition to his theoretical work in the development of the actinide concept, which placed the actinide series beneath the lanthanide series on the periodic table, he postulated the existence of super-heavy elements in the transactinide and superactinide series.
19.
This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows ( periods ).
20.
Chemistry Nobel Prize winner Glenn T . Seaborg who first proposed the actinide concept which led to the acceptance of the actinide series also proposed the existence of a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153.
