Question

Demerit of Mendeleev's periodic table

Answer 1

the demerits of mendeleev periodic table are as follows:

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.

hope it will help you.....

Answer 2

$\large\mathcal\purple{Mendeleev's\:Periodic\:Table\:!!}$

${\boxed{\tt{Definition\::-}}}$

He arranged then known Elements in order of their increasing atomic masses considering the facts that elements with similar properties should fall in the same vertical columns and leaving out blank spaces where necessary.

$\sf\small{Demerits\:Of\:Mendeleev's\:Periodic\:Table\::-}$

• Position of Hydrogen is uncertain. It has been placed in IA and VIIA groups because of its resemblance with both the groups.
• No seperate positions were given to isotopes.
• Anomalous positions of lanthanides and actindes in Periodic Table.
• Similar elements were placed in differents groups (Cu IB and Hg IIB) and the elements with different properties were placed in same groups (Alkali metals IA and Coinage metals IB).
• It didn't explained the cause of periodicity.

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