What do you understand by (i) electron-deficient, (ii) electron-precise and (iii) electron-rich compounds of hydrogen? Provide justification with suitable examples.

Explanation

(i) Electron deficient hydribes are those which donot have sufficient number of electrons to form nomal covalent bonds. For example, hydribes of group 13 `(BH_3 , AlH_3 , ` etc.). To make up their deficiency they generally exist in polymeric forms such as `B_2 H_6, Al_2 H_6 , ` etc.
(ii) Electron precise hydribes are those which have sufficient number of electrons required for forming covalent bonds. for example , hydribes of group 14 `(CH_4 , SiH_4 , GeH_4 , SnH_4 , PbH_4 , ` etc `)`. These have tetrahedral shapes.
(iii) Electron rich hydribes are those which have excess electrons as required to form normal covalent bonds. For example , hydribe of group 15 or 17 (i.e. , `NH_3 , PH_3 , H_2 O , H_2 S , H_2 Se , H_2 Te , etc.)` The excess electrons in these hydribes are present as lone pairs.