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The Development of the Periodic Table.
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Chemistry Open Book Exam: The Development of the Periodic Table By Osman Khan Lee 12 Early attempts at the Periodic Table Johann Dobereiner The first scientist to classify the elements into similar properties was the German chemist, Johann Dobereiner. He attempted to arrange them in terms of atomic weights- which we now call relative atomic mass. He identified a number of triads which he classified as having the same properties. His discovery enabled him to identify that the mass of the middle element was approximately the average of the other two. E.G. Element Relative Atomic Mass Lithium 6.9 Sodium 23 Potassium 39.1 The table above shows a triad. The middle element's relative atomic mass can be determined by calculating the average of the two around it: RAM of Sodium = (6.9 + 39.1) / 2 = 23 As well as this there were several other triads identified. However, people believed that this theory was merely coincidence, and was therefore not taken very seriously. Dimitri Mendeleev A...
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