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He developed groups of 3 elements with similar properties
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He arranged the known elements in order of atomic weights & observed similarities between some elements
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He developed an early version of the periodic table, with 28 elements organized by valence
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He produced a a table based on atomic weights but arranged periodically with elements with similar properties under each other. His Periodic Table included the 66 known elements organised by atomic weights.
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He determined the atomic number of each of the elements and modified the 'Periodic Law'.
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He synthesised transuranic elements (the elements after uranium in the periodic table)