Question

What do you understand by (i) electron-deficient, (ii) electron-precise and (iii) electron-rich compounds of hydrogen?

Answer 1

The answers to these questions are obtained by the basic definitions of these which are reliant on the number of electrons present or absent in the compounds formed by hydrogen.

Complete Solution :
We have come across various definitions regarding the electrons in which in some compounds they are less in number and in some excess in number.
Let us now refresh some of these concepts and understand the base of the terms used for this.
Firstly let us consider one by one definition.
(i) From the name ‘electron – deficient’, we can understand that there is a deficiency of electrons in that particular compound. Therefore this term can be defined as ‘Electron – deficient compounds are those compounds which do not have sufficient number of electrons required for the formation of covalent bonds.
An example for this type of compound is hydrides of group 13 like $B{{H}_{3}},Al{{H}_{3}}$ etc.

(ii) Now electron precise compounds of hydrogen are having sufficient electrons for the formation of covalent bonds and thus are reverse to that of electron deficient compounds.
The examples for this type of compounds are the hydrides of group 14 which have tetrahedral shapes like $C{{H}_{4}},Si{{H}_{4}}$ etc.

(iii) The name electron rich itself suggests that the electrons are present in excess from that required for covalent bond formation.
Therefore this can be defined as ‘these are compounds containing excess of electrons for the formation of covalent bonds’. These excess electrons can be in the form of lone pairs.
Examples for these types of compounds are hydrides of group 15 and 17 like $N{{H}_{3}},HCl,HBr$ etc.

Note: Usually some of the definitions can be written directly based on the name given but concentrate on the fact that it is mentioned as hydride and do not cite examples other than hydrides.