Mendeleev’s periodic table is an arrangement of elements in an increasing atomic mass order in a tablet form, such that it reflects similarities and trends in the behaviour of elements. Mendeleev initially arranged elements, one below the other, in the order of increasing atomic weight. Elements having similar properties are placed nearby. Elements with similar properties are found in the same horizontal row.
A tabular arrangement of elements in groups and periods which highlights the regular trends in properties of elements is defined as the periodic table. There are eighteen vertical columns known as groups in the modern periodic table which are arranged from left to right and seven horizontal rows which are known as periods.
|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 separate 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.|