1. Some elements with similar properties were placed in different groups whereas some elements having dissimilar properties were placed in same group, but iodine (127) was placed in VII group.
Example: Tellurium (127.6) was placed in VI group.
2. Some elements with higher atomic weights were placed before lower atomic masses in order to maintain the similar chemical nature of elements. This concept was called inverted pair of elements concept.
Example : 5927CO and 58.728Ni
3. Isotopes did not find any place in Mendeleev’s periodic table.
4. Position of hydrogen could not be made clear.
5. He did not leave any space for lanthanides and actinides which were discovered later on.
6. Elements with different nature were placed in one group,
Example: Alkali metals and coinage metals were placed together.
7. Diagonal and horizontal relationships were not explained.
