Question

why mendeleev did noy assign a fixed position to hydrogen in his periodic table

Answer 1

Mandeleev's periodic table was based on atomic mass. He explaind the physical and chemical properties of elements on the basis of atomic mass. In chemical properties he concentrated mainly on compounds form with Oxygen and halogens.Hydrogen has atomic mass 1 so definately it must be in 1st period but the group was confusing. He found that hydrogen forms oxides like alkali earth metal (gr.1) with formula H₂O as Na₂O. He also found that H is similar to halogens in forming diatomic molecule H₂ like Cl₂, Br_2. So he could not assign fixed position to H.