Periodic Table |
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| What is the Periodic Table Showing? | Periodicity |
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. The database holds information on periodic tables, the discovery of the elements, the elucidation of atomic weights and the discovery of atomic structure (and much, much more).
| Year: 1950 | PT id = 14, Type = formulation |
The modern periodic table is based on quantum numbers and blocks, here.
A periodic table can be constructed by listing the elements by n and l quantum number:

The problem with this mapping is that the generated sequence is not continuous with respect to atomic number atomic number, Z: Check out the sequence Ar to K, 18 to 19.
Named after a French chemist who first published in the formulation in 1929, the Janet or Left-Step Periodic Table uses a slightly different mapping:

While the Janet periodic table is very logical and clear it does not separate metals from non-metals as well as the Mendeleev version, and helium is a problem chemically.
However, it is a simple mapping to go from the Janet or Left-Step periodic table to a modern formulation of Mendeleev's periodic table:

On this page web, "full" f-block included periodic tables are shown wherever possible, as above.
However, the periodic table is usually exhibited in book and on posters in a compressed form with the f-block "rare earths" separated away from the s-block, p-block and d-block elements:
However, the compression used introduces the well known problem known as a "fence post error".
The effect is that:
La and Ac: move from f-block to d-block
Lu and Lr: move from p-block to f-blockChemically, the elements can be fitted in and classified either way. Many thanks to JD for pointing the situation with the periodic table is a fence post error.
Mark Winter's Web Elements project, here, uses the formulation shown below:
Interestingly, the IUPAC periodic table separates out 15 lanthanides, La-Lu, and 15 actinides, Ac-Lr by leaving gaps in period 3 under Sc & Y:
This corresponds to:

By Mark Leach
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| What is the Periodic Table Showing? | Periodicity |
© Mark R. Leach Ph.D. 1999 –
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