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The INTERNET Database of Periodic Tables

There are thousands of periodic tables in web space, but this is the only comprehensive database of periodic tables & periodic system formulations. If you know of an interesting periodic table that is missing, please contact the database curator: Mark R. Leach Ph.D.

Use the drop menus below to search & select from the more than 1100 Period Tables in the database:

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Seaborg's "How the Periodic Table Evolved Over 40 Years" (1939 – 1979)

From the C&EN paper THE PERIODIC TABLE: Tortuous path to man-made elements 57, 1979, pp 46-52.

Until World War II, the three heaviest known elements – thorium, protactinium & uranium – were believed to be related to hafnium, tantalum & tungsten respectively. Similarly, elements 93 to 100 were expected to fit neatly into the periodic table:

Synthesis and study of the transuranic elements – neptunium & plutonium – indicated that these new elements were "cousins" of uranium and in 1944 should be placed into a new "uranide" group.

Subsequently (1944/45), Seaborg advanced the theory that elements heavier than actinium actually constitute a distinct "actinide" group that mirrors the lanthanide rare-earth group:

Finally, Seaborg postulated what a future periodic table, up to Z = 168, may look like:

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What is the Periodic Table Showing? Periodicity

© Mark R. Leach Ph.D. 1999 –

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