What are the demerits of Mendeleev’s periodic table?

1.	What are the demerits of Mendeleev’s periodic table?
Answer» Demerits of Mendeleev’s periodic table: i. No fixed position was given to hydrogen because it resembled alkali metals as well as halogens. ii. Isotopes of same element have different atomic masses. So each of these isotopes should be given different position. But isotopes which were chemically similar had to be given same position. iii. At certain places, an element of higher atomic mass has been placed before an element of lower mass. Eg. Cobalt (Co = 58.93) is placed before nickel (Ni = 58.71). iv. Some elements placed in the same subgroup had different properties. Eg. Manganese (Mn) is placed with halogens which totally differ in the properties.

Answer»

Demerits of Mendeleev’s periodic table:

i. No fixed position was given to hydrogen because it resembled alkali metals as well as halogens.

ii. Isotopes of same element have different atomic masses. So each of these isotopes should be given different position. But isotopes which were chemically similar had to be given same position.

iii. At certain places, an element of higher atomic mass has been placed before an element of lower mass. Eg. Cobalt (Co = 58.93) is placed before nickel (Ni = 58.71).

iv. Some elements placed in the same subgroup had different properties.

Eg. Manganese (Mn) is placed with halogens which totally differ in the properties.

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