Write the drawbacks in Mendeleev’s periodic table that led to its modification.


• Some elements do not fit to his classification that was based on the atomic weights. For example, cobalt was placed before nickel, tellurium before iodine etc.


• He violated his periodic law at certain places to assign the correct position to elements on the basis of their properties.


• The position of hydrogen was not defined correctly as it resembled few characteristics of alkali metals and few of halogens.


• Position of isotopes would be different according to Mendeleev’s periodic table.


• No separate positions were given to lanthanoids and actinoids.


• Position of group VIII elements was not justified.


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