Hydrides which are deficient in hydrogen and in which the ratio of hydrogen to metal is fractional are called non-stoichiometric hydrides. This type of hydrides are formed by d-and f-block element.
Since alkali metals are highly reducing, they transfer their own electron to H atom thereby forming H- ion. Therefore the ratio of metal to hydrogen is always fixed and they form only stoichiometric hydrides. In other words alkali metals do not form non-stoichiometric hydrides.
