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Salters Open Book Paper April/May 2004 One of the earliest attempts to organise chemical elements was that of Johann Dobereiner, who was a German scientist. He noticed that there were several groups of three elements that had similar properties, and that the middle of these (when ordered by atomic weight) had a weight roughly equal to the mean of the other two. Although Dobereiner's contemporaries looked upon these discoveries as mere coincidences, they were important and the idea of trends in the properties of elements was born. Triad 1 Triad 2 Name Atomic Mass Name Atomic Mass First element calcium 40.1 lithium 6.9 Third element barium 137.3 potassium 39.1 Average mass 88.7 Average mass 23.0 Second element strontium 87.6 sodium 23.0 Doberiener's Law of Triads [1]. Note the similarities between the average mass of the first & third elements, and the second. All the elements in a given Triad have similar chemical and/or physical properties. In 1863, the British scientist John Newlands noticed that a pattern occurred in every eighth element when they...

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