The drawbacks of Mendeleev's Periodic Table are:
Position of Hydrogen was unclear
Position of Lanthanides and Actinides
Position of Isotopes
Anomalous positions of some elements
Mendeleev's table had some major drawbacks:
(i) The position of Hydrogen- Hydrogen resembles the elements of both group 1 and group 7. So, its position was controversial in the table.
(ii) The position of isotopes- On the basis of atomic masses, different isotopes of the same element should be given different positions in the periodic table. But they were assigned a single position.
(iii) The position of Lanthanides and Actinides- Lanthanides and Actinides were placed at the bottom of the periodic table. They were not placed in the regular periodic table.