Ionic or Saline Hydrides

Ionic Hydrides

Ionic hydrides form with most of the highly electropositive s-block elements and are stoichiometric compounds. Interestingly, the lighter members — $LiH$, $BeH_2$ and $MgH_2$ — show significant covalent character, and $BeH_2$/$MgH_2$ are actually polymeric solids rather than simple ionic lattices.

Physical behaviour: in the solid state, ionic hydrides are crystalline, non-volatile and do not conduct electricity. Their molten form, however, does conduct, and electrolysing the melt liberates dihydrogen at the anode — direct evidence for the existence of the hydride ion, $H^-$:

Reactivity: saline hydrides react violently with water, releasing hydrogen gas:

$NaH(s) + H_2O(aq) \rightarrow NaOH(aq) + H_2(g)$ …