Question

why do we call "electron deficient hydrides"?​

Answer 1

Electron deficient compounds. Hydrides of group 13 (i.e. BH3, AlH3etc.) have lesser electrons to form normal covalent bonds and hence are called electron deficient hydrides. ... Electron precise compounds have the required number of electrons to write their conventional Lewis structures.

Answer 2

BH3, AlH3etc.) have lesser electrons to form normal covalent bonds and hence are called electron deficient hydrides. ... They act as Lewis acids i.e. electron acceptors. (ii) Electron-precise compounds. Electron precise compounds have the required number of electrons to write their conventional Lewis structures.