Development of the Periodic Chart

synthetic elements


Edwin M McMillan (born 1907, died 1991) and Abelson discovered Neptunium in 1940.

In 1941 Glenn T. Seaborg (b1912, d1999, photo at right→), Kennedy, and Wahn, continuing McMillan's efforts, discovered PlutoniumSeaborg contributed to the discovery of many of the other transuranium elements.

Based on the unexpected difficulty isolating elements #95 and #96, Seaborg began wondering in 1944 if such elements might form an Actinide series on the periodic chart, similar to the Lanthanide series.  Upon the discovery of those elements based on that assumption, Seaborg proposed in 1945 the Actinides, like the Lanthanides, to be named for the first element in the series.  Previously Actinides were believed to be transition elements.  Note in his first version of the revised periodic chart (below↓), Seaborg cautiously located the Actinide elements (starting with element #89) in BOTH locations!  (Note the similar duplication of Hydrogen #1 and Aluminum #13.  Read more about the related discovery of elements #95 and #96.)

McMillan and Seaborg were awarded the 1951 Nobel Prize for Chemistry.  In 1997 element # 106 was named Seaborgium after Glenn Seaborg.

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created 23 March 2002
latest revision 1 May 2010
by D Trapp
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