Question
Sun November 20, 2011 By:

I am not getting the concept of fission of covalent bond, so please help me out with complete details on this topic

Expert Reply
Mon November 21, 2011
A covalent bond can get cleaved either by :
(i) heterolytic cleavage, or by (ii) homolytic cleavage.
In heterolytic cleavage, the bond breaks in such a fashion that the shared pair of electrons remains with one of the fragments. After heterolysis, one atom has a sextet electronic structure and a positive charge and the other, a valence octet with at least one lone pair and a negative charge. Thus, heterolytic cleavage of bromomethane will give  +CH3 and Br– as shown below :
 
 
In homolytic cleavage, one of the electrons of the shared pair in a covalent bond goes with each of the bonded atoms. Thus, in
homolytic cleavage, the movement of a single electron takes place instead of an electron pair. The single electron movement is shown by ‘half-headed’ (fish hook) curved arrow. Such cleavage results in the formation of neutral species (atom or group) which
contains an unpaired electron. These species are called free radicals.A homolytic cleavage can be shown as:
 
 
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