Dobereiner 's triads - wikipedia Dobereiner 's triads This article may require cleanup to meet Wikipedia 's quality standards. The specific problem is : Need to sync the masses and elements used here with those used in the actual publications not later modern refinements. Please help improve this article if you can. ( December 2013 ) Johann Wolfgang Dobereiner, who attempted to sort the elements in an order which consisted of triads. In the history of the periodic table, Dobereiner 's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Dobereiner 's observations of the alkaline earths ; namely, that strontium had properties that were intermediate to those of calcium and barium. By 1829, Dobereiner had found other groups of three elements ( hence `` triads '' ) whose physical properties were similarly related. He also noted that some quantifiable properties of elements ( e.g. atomic weight and density ) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements. Predicted vs actual atomic mass of the central atom of each triad Triad name Elements and atomic masses Element 1 Mass Element 2 Mean of 1 and 3 Actual mass Element 3 Mass Alkali - forming elements Lithium 6.94 Sodium 23.02 22.99 Potassium 39.10 Alkaline - earth - forming elements Calcium 40.1 Strontium 88.7 87.6 Barium 137.3 Salt - forming elements Chlorine 35.470 Bromine 80.470 78.383 Iodine 126.470 Acid - forming elements Sulfur 32.239 Selenium 80.741 79.263 Tellurium 129.243 - Iron 55.8 Cobalt 57.3 58.9 Nickel 58.7 References Jump up ^ Wurzer, Ferdinand ( 1817 ). `` Auszug eines Briefes vom Hofrath Wurzer, Prof. der Chemie zu Marburg '' ( Excerpt of a letter from Court Advisor Wurzer, Professor of Chemistry at Marburg ). Annalen der Physik ( in German ). 56 : 331 -- 334. From pp. 332 -- 333 : `` In der Gegend von Jena ( bei Dornburg )... Schwerspaths seyn möchte. '' ( In the area of Jena ( near Dornburg ) it is known that celestine has been discovered in large quantities. This gave Mr. Dobereiner cause to inquire rigorously into the stoichiometric value of strontium oxide by a great series of experiments. It turned out that it ( i.e., the molar weight of strontium oxide ) -- if that of hydrogen is expressed by 1 or that of oxygen is expressed by the number 7.5 -- is equal to 50. This number is, however, precisely the arithmetic mean of that which denotes the stoichiometric value of calcium oxide ( = 27.55 ) and of that which denotes the stoichiometric value of barium oxide ( = 72.5 ) ; namely ( 27.5 + 72.5 ) / 2 = 50. For a moment, Mr. Dobereiner found himself thereby caused to doubt the independent existence of strontium ; however, this withstood both his analytical and synthetic experiments. Even more noteworthy is the circumstance that the specific weight of strontium sulfide is likewise the arithmetic mean of that of pure ( water - free ) calcium sulfide and that ( i.e., the sulfide ) of barium, namely ( 2.9 + 4.40 ) / 2 = 3.65 ; which must cause ( one ) to believe even more that celestine might be a mixture of equal stoichiometric amounts of anhydrite ( i.e., anhydrous calcium sulfate ) and barite. ) ^ Jump up to : Dobereiner, J.W. ( 1829 ). `` Versuch zu einer Gruppirung der elementaren Stoffe nach ihrer Analogie '' ( An attempt to group elementary substances according to their analogies ). Annalen der Physik und Chemie. 2nd series ( in German ). 15 : 301 -- 307. For an English translation of this article, see : Johann Wolfgang Dobereiner : `` An Attempt to Group Elementary Substances according to Their Analogies '' ( Lemoyne College ( Syracuse, New York, USA ) ) Jump up ^ `` Johann Wolfgang Dobereiner ''. Archived from the original on 2016 - 03 - 23. Retrieved 2016 - 03 - 23. `` A Historic Overview : Mendeleev and the Periodic Table '' ( PDF ). Retrieved 2013 - 01 - 15. Retrieved from `` https://en.wikipedia.org/w/index.php?title= Döbereiner % 27s_triads&oldid = 864170799 '' Categories : History of chemistry Classification systems Hidden categories : CS1 German - language sources ( de ) Articles needing cleanup from December 2013 All pages needing cleanup Cleanup tagged articles with a reason field from December 2013 Wikipedia pages needing cleanup from December 2013 All pages needing factual verification Wikipedia articles needing factual verification from March 2018 Talk About Wikipedia Dansk Magyar മലയാളം ਪੰਜਾਬੀ پنجابی Polski සිංහල Edit links This page was last edited on 15 October 2018, at 15 : 18 ( UTC ). About Wikipedia

Question: who organized known elements by placing them into groups of three called triads
Answer: Johann Wolfgang Dobereiner