Question

What are the defects of Mendeleev’s periodic table?

Answer 1

As we know that Mendeleev’s periodic table was introduced by the Russian chemist, Dmitri Ivanovich Mendeleev. He worked on 63 elements which were known till then and after studying the properties of each element, he found that the properties of elements were related to their atomic mass in a periodic way and gave his periodic table. So here we have to explain the defects of Mendeleev’s periodic table.

Complete answer:
Let us discuss the defects of Mendeleev’s periodic table as follows:-
-Anomalous Pairs: The following pairs of elements shown don’t follow the principles of Mendeleev:
Cobalt (58.9) has a higher atomic mass than Nickel (58.6) but precedes it in the periodic table.
Tellurium (127.6) has a higher atomic mass than Iodine (126.9) but precedes it in the periodic table, hence not according to the principles instructed by Mendeleev.
-Grouping of chemically dissimilar elements: Elements such as Cu and Ag have no resemblance with the alkali metals but they are still placed together in the first group according to his table.
-Position of Isotopes: The later found isotopes of an element must be given separate places in his periodic table because they have different atomic masses but it was completely neglected.
-Electronic arrangement: It does not give any explanation regarding the electronic arrangement of elements.
-Separation of chemically similar elements: Elements which are chemically similar like Gold and Platinum have been placed in separate groups which were completely wrong.
-The position of hydrogen: Hydrogen was not given a fixed position in this periodic table.

Note:
-Remember that even after having so many defects his table was proven to be the origin of modern periodic table because the trend he gave regarding elements’ atomic masses and hence he is also known as the father of Modern periodic table.