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The difference between Mendeleev and modern periodic table is that Mendeleev’s periodic table was based on the increasing atomic masses while the modern periodic table is based on the increasing atomic numbers. Mendeleev is the pioneer of the modern periodic table, though a numerous number of changes had been made to the old version of the periodic table.

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The most important difference between Mendeleev's periodic table and modern periodic table is that Mendeleev took increasing atomic mass as the periodic property whereas in modern periodic table, it is increasing atomic number.

Another difference is that there were only 66 elements in Mendeleev's table whereas there are 118 elements.