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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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Moseley's Periodic Law

Henry Moseley (1887-1915) subjected known elements to x-rays and was able to derive a relationship between x-ray frequency and number of protons.

From Scientific American:

"It was the clever young English physicist, Moseley, who discovered that the atomic number for each element was the number of external electrons in the atom.

"With this discovery came a law concerning the X-ray lines of any element in an X-ray target.

"Moseley's law states that the wavelength of these lines is inversely proportional to the square of the atomic number of the element. Therefore, if we know the atomic number of the element we are looking for, we can predict the wavelength of certain lines in its X-ray spectrum.

"If we set up our X-ray spectrograph so as to catch these lines where we expect them to fall, then, if the element is present in the target which we have chosen to use in our X-ray tube, we should know it. This provides one good way to identify difficult elements, but it is well to have another to use as a check. One of the best of these, and one which is almost as sensitive as the X-ray method, is that of positive ray analysis."

From his paper, The High Frequency Spectra of The Elements, H. G. J. Moseley, M. A. Phil. Mag. (1913), p. 1024, available here:

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What is the Periodic Table Showing? Periodicity

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