Question

what are the merits and demerits of mendeleevs table?

Answer 1

Merits:
Elements were horizontally arranged according to atomic mass.
Elements were arranged in vertical columns called groups according to their resemblance in properties.
The periodic table had 8 groups and 7 periods.
Since only 63 elements were known at that time, he had left gaps for undiscovered elements.
Demerits :
Position of hydrogen: Hydrogen is placed in group 1A. It resembles the elements of group IA as well as elements of group VII A. Thus, position of hydrogen in the periodic table is not clear.
Position of isotopes: On the basis of atomic mass, various isotopes of the same element should be assigned different places in the periodic table. However, no separate place was assigned to the isotopes.
Similar elements placed separately: certain chemically similar elements have been placed in different groups, e.g. similar elements such as Cu and Hg have been placed in different groups.
Dissimilar elements placed together: curtain elements having very few similarities with other elements were grouped together, e. g. Mn has been placed in group VII.
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Answer 2

Answer:

Merits:-

1. elements are arranged by systamatic manner i.e similar properties

2. he left some gaps in discovered foe new elements

3. new elements are called 'eka' element

   Eka  Boran ⇒Sc

   Eka Aluminium⇒Ga

   Eka Silicon⇒Ge

   Eka Manganese⇒Tc

4. mendeleev's periodic table has helped in correction of doubtful atomic weigths.

        [Atomic weigths = valency × equivalent]

5. initially it was found that equivalent weight of Be is 4.5 a it is trivalent [v=3] so weight of Be was 13.5 and there is on space in mendeleev's table

6. After correction it was found that Be is actually divalent. so weight ofBe become 2×4.5=9

Explanation:

Demerits:-

1.  position of hydrogen [hydrogen resemble the alkalimetal as well as halogens  ∴It maybe placed 1 A {OR} 7 A thus the position of H is not clear].

2. position of isotopes [on the basis of atomic masses different isotopes of the periodic table . but they should be placed at the same place due to similar chemical properties].

3.similar elements separated in the table

Ex:- certain elements such as Cu &Hg[OR] Au&Pt  which posses similar chemcial properties are placed in different groups

4. dissimilar elements placed in same group

Ex:- Li Na K grouped with Cu Ag Au are properties are different.

HOPE IT HELPS YOU ; )))