Molecular hydrides are classified into electron deficient, electron precise and electron rich compounds.

B₂H₆ is an electron deficient hydride. These have an incomplete octet. They are formed generally by the group 13 elements like B, Al, etc.

Structure of B₂H₆

An electron-precise hydride is a type of hydride which has the exact number of electrons required to form normal covalent bonds, no excess no deficient. These are formed generally by group 14 elements like Si and C which have 4 valence electrons.

Eg. CH₄ , SiH₄, etc.

Structure of CH₄

NH₃, H₂O are examples of electron rich hydrides. These contain excess number of electrons on the central atom called lone pairs. These are formed by group 15,16,17 elements like N, O, F, etc.

Structures of NH₃ and H₂O