Merits and demerits of mendleevs periodic table
Answers
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.
1. systematic arrangements of 66 elements in groups and periods.
2. corrected doubtful masses of some elements like Be,Pd,Pt etc.
3. predicted properties of elements which were not discovered -like scandium , gallium , germanium , which were correct and left gaps for them.
demerits-
1. controversial position of hydrogen.
2. position of isotopes were not correct.
3. two similar elements like Cu & Hg were grouped differently.
4. Co with higher atomic no. was placed before lower atomic no. Ni which was contradicting arrangement of element in increasing atomic no.