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When did Dmitri Mendeleev present his first periodic table?

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Dmitri Mendeleev presented his first periodic table in 1869.1

While earlier chemists had attempted to classify chemical elements based on properties or atomic weight, Mendeleev’s innovation was to arrange them by atomic weight while also accounting for their valence. His initial 1869 table featured 17 columns, which he later refined into an eight-group table in 1871. This later version became particularly famous for his accurate predictions regarding the existence and properties of then-undiscovered elements.12