Question

Compare and contrast the arrangement of elements in Mendeleev’s periodic Table and the Modern Periodic Table.

Answer 1

Mendeleev’s periodic table	Modern periodic table
Elements are arranged in the increasing order of their atomic masses.	Elements are arranged in the increasing order of their atomic numbers.
There are 8 Groups.	There are 18 Groups.
Each groups are subdivided into sub group ‘a’ and ‘b’	Groups are not subdivided into sub-groups.
Groups for Noble gas was not present as noble gases were not discovered by that time.	A seprate group is meant for noble gases.
There was no place for isotopes.	This problem has been rectified as slots are determined according to atomic number.