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The limits of Mendeleev’s insight

Abstract Between his initial proposal in February 1869 and his final table of November 1870, Mendeleev made radical improvements, linking his groups to highest oxidation states, clarifying the relationship of element and substance, and making detailed predictions of the properties of three missing elements. However, his inflexible belief in an alternating structure of rows of VII and VIII groups made it impossible for him to include the ‘rare earths’, and the relationship between the two rows of VII at the top confused the system. From 1873 onwards, other interests prevented him from thinking about his table, apart from accommodating the noble gases. His final table of 1906 shows no significant advance on that of 1870, and indeed, the top row contains absurd guesses about elements around hydrogen.