How does Mendeleev’s version of the periodic table differ from the modern one?
While the first edition of Mendeleev’s table contained 63 elements, the current periodic tables include 118 elements.
Mendeleev used the horizontal format in his versions, and now chemical 'groups' are shown vertically.
Mendeleev's periodic table is based on atomic mass while today's periodic tables are arranged by increasing atomic numbers.
Mendeleev placed transition elements together with other elements, and the modern periodic table shows these elements in a separate block.
Not discovered at that time noble gases were not placed by Mendeleev in his table, but nowadays these elements are in a separate group named Group-18.
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