Question

what are the demerits of Mendeleevs periodic table ?​

Answer 1

Answer:

Defects of Mendeleev's periodic table:

1. Position of hydrogen is uncertain. It has been placed in 1A and 7 th A groups because of its resemblance with both the groups.
2. No separate positions given for isotopes.
3. No separate group for lanthanides and actinides.
4. Although there is no resemblance expect valency of subgroups A and B , they have been put in the same group.
5. The order of increasing weights is not strictly followed in the arrangements of elements in the periodic table. For example, Co(At.wt.58.9) is placed before Iodine (At.wt.127) and At(At.wt.39.9) before K(At.wt.39).

Answer 2

Explanation:

Here are some demerits of Mendeleev

periodic table:

1. Elements such as copper and silver bear no resemblance but they were placed together in the first group.
2. Elements that are chemically similar,such as gold and platinum have been placed in seperate groups.
3. It does not explain the electron arrangment of elements.
4. Hydrogen was not given a fixed position. It was considered in group IA as well as in group VII A .
5. According to Mendeleev's periodic law, isotopes of an element must be given seperate places in the periodic table since they have different atomic masses. But they were not assigned different places.

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