Question

state demerits of mendeleev's periodic table​

Answer 1

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$\sf\red{⟶}$He was unable to locate hydrogen in the periodic table.

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$\sf\red{⟶}$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.

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$\sf\red{⟶}$Later on, isotopes of elements were found which violated Mendeleev’s periodic law.

Answer 2

Explanation:

i. Mendeleev could not assign a correct position to hydrogen in the periodic table as hydrogen resembles alkali metals as well as halogens.

ii. Isotopes had to be given the same position in the periodic table though isotopes of the same elements have different atomic masses.

iii. It was observed that at certain places, an element of higher atomic mass Cobalt (Co=58.93) has been placed before an element of lower atomic mass Nickel (Ni = 58.71).

iv. Some elements placed in the same sub - group varies in their properties. Manganese is placed with halogens which totally differ in the properties

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