Answer:
Disadvantage: the isotopes and no separate position also as they have different atomic mass but same atomic number. Since the change in atomic mass of two successive elements was not constant therefore it was difficult to predict the number of missing elements with the help of atomic number only.
It could predict the existence of other elements and could predict their properties so, as to leave space in the periodic table. It could accommodate all the sixty elements discovered at that time and could accommodate the noble gases which, where discovered later.
