What are the merits of Mendeleev's periodic table?
- Characteristics of science:-
Science is a process and has the freedom to revise the old inference by using more advanced means and methods of doing experiments. It is seen in Mendeleev's periodic table.
- Proper places:-
Atomic masses of some elements were revised to give them a proper place in the periodic table following their properties.
- Vacant places:-
Mendeleev kept vacant places for the elements not discovered till then in the periodic table.
- No places reserved for noble gases:-
There were no places reserved for noble gases in Mendeleev's periodic table. But Mendeleev organized the zero group without disturbing the original periodic table in which noble gases were fitted very well towards the end of the 19th century.
Mendeleev's periodic table
The Russian scientist, Dmitri Mendeleev, developed the periodic table of elements during the period 1869 to 1872 A.D. He created the periodic table based on the chemical and physical properties of the elements which are the molecular formula of hydride and oxide of the elements, melting & boiling points and density of the elements with their atomic mass. He also selected that the element which has similar physical and chemical properties repeat after a definite interval. That is, the properties of elements are periodical functions of their atomic masses.
What are the demerits of Mendeleev's periodic table?
- Ambiguity:-
There was ambiguity regarding their sequence in Mendeleev's periodic table as the atomic mass of element Cobalt (Co) and nickel (Ni).
- No place for isotopes:-
Isotopes were discovered long times after Mendeleev put forth the periodic table. (Isotopes have the same chemical properties, but the different atomic mass is called isotopes.)
Increasing order of atomic masses does not appear to be uniform:-
It was not possible to predict how many elements could be discovered between heavy elements when elements are arranged in increasing order of atomic masses.
Position of hydrogen:-
Hydrogen shows similarity with halogen. In the same way, there are some similarities in the chemical properties of alkali metals. Therefore, it cannot be decided the correct position of the hydrogen.
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