Johann Dobereiner (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-
Queries, Suggestions, Bugs, Errors, Typos...
If you have any:
Suggestions or periodic table representations not shown on this page
Suggestions for links
Bug, typo or grammatical error reports about this page,
please contact Mark R. Leach, the author, using email@example.com
This free, open access web book is an ongoing project and your input is appreciated.