All Group I and II elements, except beryllium, form hydrides by
direct combination with hydrogen. The hydrides of the metals
except those of beryllium and magnesium, are white mainly ionic
solids, all Group I hydrides having the sodium chloride lattice
structure. All the hydrides are stable in dry air but react with water,
the vigour of the reaction increasing with the molecular weight of
the hydride for any particular group.