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: Dr Mark R Leach.
Use the buttons below to select from the 1000+ Periodic Tables in the database:
Johann Döbereiner 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.
Döbereiner writes in An Attempt to Group Elementary Substances according to Their Analogies (in English)
From Poggendorf's Annalen der Physik und Chemie 15, 301-7 (1829) (in German) [from Henry M. Leicester & Herbert S. Klickstein, eds., A Source Book in Chemistry, 1400-1900 (Cambridge, MA: Harvard, 1952)]:
"The work of Berzelius on the determination of the atomic weights of bromine and iodine has interested me greatly, since it has established the idea, which I expressed earlier in my lectures, that perhaps the atomic weight of bromine might be the arithmetical mean of the atomic weights of chlorine and iodine. This mean is (35.470+126.470)/2 = 80.470. This number is not much greater than that found by Berzelius (78.383); however, it comes so close that it may almost be hoped that the difference will vanish entirely after repeated careful and exact determinations of the atomic weights of these three salt-forming elements. This idea was the motive for an attempt which I made twelve years ago to group substances by their analogies."
[Note: L&K noticed an error in the above math: (35.47 + 126.47)/2 = 80.97 not 80.47. Whoops...]
The diagram below 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:
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