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.

Explanation

The hydrides in which the ratio of the metal to hydrogen is fractional and does not correspond to actual formula are called non-stoichiometric hydrides. Their composition varies with temperature and pressure. For example, the hydrides of titanium or zirconium are represented as `TiH_x` (x= 1.8 to 2) and `Zr H_x` (x = 1.30 to 1.75) respectively. This type of hydrides are formed by elements of d-and f-block.
Alkali metals are very strong reducing agents and they transfer their lone electron to H-atom to form `H^(-)` ion. In other words, alkali metal hydrides are ionic in which `H^-` ions occupy holes of lattice. Since hydride ion is formed by the transfer of an electron, therefore, the ratio of metal to hydrogen is always fixed and hence alkali metals form only stoichiometric hydrides. Thus, alkali metals donot form non-stoichiometric hydrides.