Question

write the merits and demerits of Mendeleev's periodic table(3 points )

Answer 1

Merits are as follows:-
 1. There was a regular gradation in physical and chemical properties of elements.
 2. The group number of an element indicates highest oxidation state that it can attain.
 3. There were many vacant spaces in Mendeleev's periodic table for the elements to be discovered. He  named them Eka-Boron, Eka-Aluminium and Eka-silicone He also predicted the properties of these  undiscovered elements including atomic masses. These elements were discovered as Sc ,Ga and Ge  with same features as he predicted.
 4. Mendeleev’s arrangement helped to correct atomic masses of a number of elements.

Demerits are as follows:-
 1. The elements, if arranged according to their atomic weights show an evident periodicity of  properties. 
 2. Elements which are similar as regards their chemical properties have atomic weights which are either  nearly the same value or which increase regularly. 
 3. The arrangement of the elements or of groups of elements in the order of their atomic weights,  corresponds with their so called valencies. 

Answer 2

merits:-

arranged elements in rows called periods and columns called groups

he arranged elements based of their properties and atomic mass

helped find new elements as Mendeleev had left spaces for these “probably” yet to be discovered elements and even gave the properties of the same which were later found true . eg;gallium(eka Al) and germanium (eka Si)

his predictions came out sucessful

demerits:-

he didn’t know where to place hydrogen as it possessed a dual nature of both alkali metals and halogens

he arranged elements according to atomic mass but at places placed elements with more atomic weight before a lighter one .so his table was modified by using atomic number instead of atomic mass to the present “modern periodic table “