Question

Question 9.11 What do you understand by the term “non-stoichiometric hydrides”? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Class XI Hydrogen Page 289

Answer 1

These type of hydrides are formed by many d - block ( except metal of 7 , 8 , 9 group) and f-block elements. these hydrides are always non- stoichiometric.in these hydrides , hydrogen atom occupies interstitial sites. e.g., LaH₂.₈₇, TiH₁.₅_₁.₈, etc

These types of hydrides are not formed by alkali metals . alkali metals form ionic or saline hydrides . Saline hydrides are stoichiometric . alkali metals are highly electropositive, they transfer of their electron to the H-atom.
by which H- ions form and these H- ions occupy holes in the lattice.

Answer 2

Answer:

Hydrides which are deficient in hydrogen and the ratio of the metal to hydrogen is fractional are non-stoichiometric hydrides.

Explanation:

This type of hydrides are formed by d-block and f-block elements. In these hydrides, the hydrogen atoms occupy holes in metal lattice. Usually some holes always remain unoccupied and hence these metals form non-stoichiometric hydrides.

Since alkali metals are highly reducing, they transfer their lone electrons to H atom,  thereby forming $H^{-}$ ion. In other words, alkali metals hydrides are ionic in which $H^{-}$ ions occupy holes in lattice. Since hydride ion is formed by complete transfer of an electron, therefore, the ratio of metal to hydrogen is always fixed and hence alkali metals form only stoichiometric hydrides.