merits and demerits of Mandlev
Answers
Merits of Mendeleev Periodic Table
Some gaps were left for the elements yet to be discovered. Thus, if a certain new element is discovered, it can be placed in a new group without disturbing any existing group.
Demerits of Mendeleev Periodic Table
He was unable to locate hydrogen in the periodic table.
Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.
Later on, isotopes of elements were found which violated Mendeleev’s periodic law.
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.