Hi Snoby.. !!!!
Limitations are :
Position of hydrogen : Hydrogen is placed in Group IA. However, it actually resembles the elements of Group-IA (alkali metals ) as well as the elements of Group VII-A (halogens ). Thus, the position of hydrogen in the periodic table is not clear.
Position of isotopes : On the basis of atomic weight , various isotopes of the same elements should be assigned different places in the periodic table. Mendeleev could not provide separate places for isotopes.
Position of lanthanides and actinides : Fourteen elements following Lanthanum(known as lanthanides or rare earths) and the fourteen elements following Actinium (known as actinides or transuranic elements ) have not been provided separate and proper places in the Mendellev 's table, rather they have been placed in two rows at the bottom of the table.
Disimilar elements placed together : Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.
Similar elements separated : In Mendeleev 's periodic table, certain chemically similar elements such as copper and mercury ; gold and platinum have been placed in different groups.
Anomalous pairs : In the Mendeleev 's Table based on atomic weight, the positions of certain pairs , e.g. Argon( at. wt = 39.94) and potassium ( at. wt = 39.1) : Cobalt( at wt =58.93 ) and nickel ( at wt = 58.71 ) ; Tellurium at wt = 127.60) and iodine (atomic weight = 126.90 ) would be reversed. In other words, certain pairs of elements are misfit in the periodic table, if atomic weight is the basis of classification.
Hope this helps !!!!!!