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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.

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Year:  1939 PT id = 1056

Foster's Periodic Arrangement

L.S. Foster, "Why not modernise the textbooks also? I. The periodic table", Journal of Chemical Education, vol. 16, no. 9, pp. 409–412,

Foster writes:

"The [above] modern periodic table is simply an orderly array of the elements with all unnecessary ornamentation omitted, has been found highly satisfactory for instructional purposes.

"The transitional elements, with two unfilled electron shells, are separated from the non-metallic elements.

"The rare-earth elements, defined as those with three incomplete electron shells, are shown to be those of atomic numbers 58 to 70, while La and Lu, which have only two incomplete electron shells are classified as transitional elements.

"Copper, silver, and gold act as transitional elements except when the state of oxidation is one."

René Vernon writes:

Foster couldn't show the coinage metals – with their full d10 complements – as transitional elements, but by adding a broken line around them he was showing they had the capacity to act as if they were.

I tried to work out how he distinguished La & Lu from Ce to Yb. Foster seems to be saying that La 5d1 6s2, has incomplete 5th and 6th (ie. 6p) shells.

Same for Lu 4f14 5d1 6s2 having incomplete 5th and 6th shells. Whereas, for example, Ce 4f1 5d1 6s2 has incomplete 4th, 5th and 6th shells. Presumably this was in the years before the fact that the 4f shell became full at Yb was widely appreciated. So, strictly speaking, group 3a should have read:

On the other hand, Yb3+ has an f13 configuration, so it does meet his three unfilled shells criterion. Had he known, he probably would've put a broken line around Yb to indicate its full f14 complement but that it normally acted as a rare earth, with an incomplete 4f shell; whereas neither La nor Lu have this capacity.

Good to see Foster put so much thought into organising his table, and his experience with using it for instructional purposes.

Van Spronsen does not mention Forster's table. Mazurs has a reference to Foster's table but lumps it in with the other medium-long tables, not appreciating its subtlety.

Mark Leach writes:

This formulation is very much like the XBL 769-10601, Periodic Table Before World War II used by Seaborg and the Manhattan project and is a precursor to the modern periodic table.

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What is the Periodic Table Showing? Periodicity

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