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The Development of the Periodic Table
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Skills for Chemistry - Open Book Paper By Sarah Newton 6B2 The Development of the Periodic Table During the 19th Century there were several scientific breakthroughs regarding classifying, ordering and predicting elements. The first came from Johann Dobereiner in 1829. He ordered all the known elements by atomic weight, (relative atomic mass) and began to identify triads. These were groups of three elements which had similar properties, and whose middle element's mass had an approximately the average masses of the other two. The first triad he noted was Barium, Calcium and Strontium. These elements are found consecutively in Group 2. 1 Triad 1 Triad 2 Triad 3 Mass of First Element Calcium = 40.1 Chlorine = 35.5 Sulphur = 32.1 Mass of Third Element Barium = 137.3 Iodine = 126.9 Tellurium = 127.6 Average of First and Third 88.7 81.2 79.9 Actual Mass of Second Element Strontium...
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