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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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Leach's Empirical Periodic Table

The common/conventional/standard 'medium form' periodic table is based on the 1945 Seaborg formulation, and it is interesting to explore where this formulation – and its 1939 predecessor – come from. (Interestingly, the Werner formulation of 1905 is not cited as a source and there are no other similar formulations in the (this) Periodic Table Database.)

However, it is possible to get to the common/conventional/standard periodic table directly from two readily available data-sets: (1) first ionisation energy of the gas phase atoms, and (2) atomic radius.

The procedure involved plotting the data, rotating 90°, squeezing vertically and smoothing. The points need a little tidying up, and then they can be mapped directly onto the Seaborg formulation periodic table.

The only element which does no obviously 'line-up' with the periodic table is hydrogen, but many modern periodic tables have H floating as it is not obvious if it should be considered to be a Group 1 alkali metal or a Group 17 halogen.


There are advantages and disadvantages to each data set. The 1st ionisation energy data from NIST is known with up to seven significant figures of precision, but the data jumps about at times due to the presence of the s & p-orbitals, which appears to make the data a little noisy. (Actually, this 'noise' is embedded information about the electronic structure of the atoms.) The atomic radius gives smoother data, but as gas phase atoms do not have hard edges calculated (Clementi 1967) rather than experimental values, must be used.

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What is the Periodic Table Showing? Periodicity

© Mark R. Leach Ph.D. 1999 –

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