Periodic Table
T-Shirts & more
from the

Merch Store

previous home next

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:

  Text Search:       

Periodic Tables from the year 1829:

1829   Döbereiner's Triads
1829   Discovery of Thorium


Döbereiner's Triads

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:

Top of Page


Discovery of Thorium


Thorium, atomic number 90, has a mass of 232.038 au.

Radioactive element with a very long half-life.

Thorium was first observed or predicted in 1829 by J. Berzelius and first isolated in 1914 by D. Lely, Jr. and L. Hamburger.

Top of Page

previous home next
What is the Periodic Table Showing? Periodicity

© Mark R. Leach Ph.D. 1999 –

Queries, Suggestions, Bugs, Errors, Typos...

If you have any:

Suggestions for links
Bug, typo or grammatical error reports about this page,

please contact Mark R. Leach, the author, using

This free, open access web book is an ongoing project and your input is appreciated.