The INTERNET Database of Periodic Tables
|2019 has been designated the International Year of the Periodic Table as it is the 150th Anniversary of the formulation of Mendeleev's Tabelle I|
Johann Döbereiner (1780 - 1849) found 'triads', a sequence of three similar elements, where the middle element has a mass equal to the average of the least and most massive. A brief biography can be found on the Nature website.
The diagram below, updated from here, uses mid-nineteenth century atomic mass information rather than modern data. If atomic numbers (Z) are used (a property unknown in 1850), the triads are exact:
|Periodic Table, What is it showing?||
© Mark R. Leach 1999-
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