(a) State the periodic law on which Mendeleev’s periodic table was based. Why and how was this periodic law changed ?

(b) Explain why, the noble gases are placed in a separate group.

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1 Answers

(a) According to Mendeleev’s periodic law: The properties of elements are a periodic function of their atomic masses. It was the discovery of atomic number which led to a change in Mendeleev’s periodic law which was based on atomic mass.

(b) The noble gases are placed in a separate group because they are chemically very inert or unreactive (having completely filled outermost electron shells).

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