Question

what are the defects of Mendeleev periodic table​

Answer 1

the defects of mandeeleve periodic table Is

1.he did not leave gaps between table for undiscovered element.

2.he couldnot place space for hydrogen.

Answer 2

Mendeleev placed elements according to their similarities in properties and not in increasing order of their atomic masses. Thus, the position of these elements was not justified e.g. cobalt (atomic mass 58.9) was placed before nickel (atomic mass 58.6)

When Mendeleev arranged the elements in order of increasing atomic mass, the properties where repeated. ... He corrected the known atomic masses of some elements and he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered.

He was unable to locate hydrogen in the periodic table. Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.