Question

why mendeleev could not assign a fixed position for hydrogen in the 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 halogensHydrogen 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.‘l) with formula H20 as NaZO. He also
found that H is similar to halogens in forming
diatomic molecule H2 like CIZ, Brz So he could
not assign fixed position to H.

Answer 2

Mendeleev couldn't assign a fixed position to hydrogen in his periodic table -->

1) Hydrogen has properties similar to alkali metals (sodium, potassium,lithium).It reacts with chlorine to form HCl. Even Na, K, Li react with Cl to form NaCl ,  KCl, LiCl respectively. All have similar general formula (RCl).

2) Hydrogen also has similar properties as that of halogens (Cl , F, Br). Like halogens  hydrogen is diatomic element.

So Mendeleev was unable to assign a proper place to hydrogen.

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