Following are the defects in the Mendeleev periodic table:
- Anomalous Pairs
The following pairs of elements don’t follow the follow Mendeleev’s Principles:
Cobalt (58.9) with a higher atomic mass precedes Nickel (58.6) in the periodic table.
Tellurium (127.6) with a higher atomic mass than Iodine (126.9) precedes it in the periodic table.
- Grouping of chemically dissimilar elements
Elements such as Copper and Silver bear no resemblance with the alkali metals, but they have been placed together in the first group.
- Position of Isotopes
According to Mendeleev’s Periodic Law, isotopes of an element must be given separate places in the periodic table because they have different atomic masses.
- Electronic arrangement
It does not explain the electronic arrangement of elements.
- Separation of chemically similar elements
Elements that are chemically similar such as Gold and Platinum have been placed in separate groups.
- The position of hydrogen
Hydrogen was not given a fixed position because it was considered in Group IA as well as in Group VIIA.