1)For placing the elements in proper groups, the order of the elements according to atomic mass was reversed in certain cases. He placed Iodine (127) after Tellurium (128) Potassium (39) and Ni (58) after Co (59). Which is against his periodic law but correct according to properties.
2. Mendeleev’s periodic table does not provide a clear idea about the structure of atom.
3. Lanthanide and Actinide have been assigned places in the periodic table which is against the periodic law.
4. Alkali metal and coinage metals (Cu, Ag and Au) which differ widely in properties are placed into the same group.
5. There is no separate position for isotopes in his periodic table.
6. The change in atomic mass of two successive elements is not constant. Hence it is not possible to predict the number of missing elements by knowing the atomic masses of two known elements.