Question

Why could no fixed position be given to hydrogen in Mendeleev's periodic classification?

Answer 1

It is so because hydrogen has 1 valence electron in its outermost shell.so according to modern periodic table, hydrogen can be arranged in halogen family i.e. group no. 17 but hydrogen does not possess the properties of halogen family. That's why hydrogen is given its position in the first group and first period of the modern periodic table.

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