How did the modern periodic table rectify various problems of Mendeleev classification?
Three different points are required
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Answers
the defects in Mendeleev's periodic table are-
1.Electron arrangement -It does not explain the electron arrangement of elements
2. Grouping of chemically dissimilar elements- elements such as copper and silver bear no resemblance to alkali metals but they have been placed together in the first group.
3. Position of Hydrogen- hydrogen was not given to fix position . it was considered in group 1A as well as group 7A because it forms both a positive Ion .
4. Separation of chemically similar elements- elements that are chemically similar such as gold and Platinum have been placed in separate groups
5. Position of isotopes- according to Mendeleev periodic law isotopes of an element must be given separate places and the periodic table since they have different atomic masses. but they were not assigned separate places
1.) mendeleeves Periodic Table::-
No fixed place could be given to hydrogen as it formed compounds similar to the halogens
Modern Periodic Table
As hydrogen atomic no. was 1 , it had a fixed place in the modern Periodic Table.
2.) Mendeleeves Periodic Table
Elements such as Cobalt and Nickel had their places exchanged i.e Nickel's atomic mass was less than cobalt but still nickel was placed after cobalt.
Modern periodic table
As , elements were arranged according to their atomic number , there was no issue about cobalt and nickel . Also, nickel was placed after cobalt as its atomic number was greater than cobalt.
3.) Mendeleeves Periodic Table
There was no place for isotopes of elements.
Modern periodic table
As elements were arranged according to their atomic numbers, there was no issue about isotopes. As we know that isotope of elements are those with same atomic no.s but different atomic masses.
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