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

Explanation

Molecular hydrides are classified on the basis of the process of the total number of electrons and bonds in their Lewis structures as:
1. Electron-deficient hydrides
2. Electrons precise hydrides
3. Electrons rich hydrides
An electrons deficient hydride has a very few electons, less than that required for representing its coventional Lewis structure e.g. diaborane `(B_(2)H_(6))`. In `B_(2)H_(6)` there are six bonds in all, out of which only four, bonds are regular two centered two electrons are shared by three atoms. Hence, its conventional Lewis structure cannote be drawn. An electron precise hydride has a sufficient number of electrons to be represented by its conventional Lewis structure e.g.`CH_(4)`. The Lewsi Structure can be written as:

Four regular bonds are formed where two electrons are shared by two atoms. An electrons rich hyrides contains excess electons as lone pairs e.g. `NH_(4)`

There are three regular bonds in alll a lone pair of electrons on the nitrogen atom.