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Johann Wolfgang Dobereiner (1780-1849), the German chemist. He improved organic analysis, studied the action of catalysts, and made the first estimates of the abundance of elements in the Earth's crust. His main claim to fame is his observation of triads of elements. These are groups such as chlorine, bromine and iodine in which the atomic mass of the middle element is close to the mean of the first and last elements in its group; and its physical and chemical properties likewise appear average. By 1829 this was developed as the Law of Triads. It attracted little attention then, but can now be seen as a step towards the Periodic Classification of the elements.
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