Why is a significant covalent character found in lighter metal hydrides like LiH , BeH2 , MgH2?

Hi

Covalent character is predominant in the compounds of beryllium, because of its small size and high nuclear charge. Beryllium and magnesium form many covalent compounds whereas the compounds of other metals of the group are essentially those of dipositive (M2+ ) ions.

Since the polarizing power of the cations is much greater, the compounds of Be and Mg have appreciable covalent character,

The extremely small size of Be2+ makes it so strongly polarizing that Be (II) compounds are almost covalent in nature. The number of covalent bonds can even be increased to four by donation and the use of sp3 hybrid orbitals, provided electron rich ligands are available. For the elements Ca to Ra, although M2+ ions are smaller than the corresponding M+ ions of alkali metals, they have low polarizing power and compounds are largely ionic. Magnesium as M2+ forms compounds, which are ionic as well as covalent in nature.