Question

How many types of cleavage are there?

Answer 1

Cleavage of any bond happens in accordance to the electronegativity difference. The atoms which are more electronegative in nature then the atom attached to it forms a polar bond and do cleavage where the negative charge moves towards more electronegative atom. Where there is no difference in electronegativity the cleavage happens in such a way that each atom has one electron.

Complete step-by-step answer:
There are two types of cleavage, as similar to the types of bond forms. We know that the formation of any bond can happen in accordance with the ability of atoms to share electrons with each other or ability to donate electrons or accept electrons.

When the bond forms by the donation of electrons by one atom and acceptance of an electron by another atom, the form is known as ionic bond. This is generally formed with metals while the other type of bond formed by sharing of electron clouds of each other, this is known as covalent bond.

We know there are atoms on the right hand side of the periodic table which are more electronegative and when they form bonds they attract the shared pair of electrons towards them and make the bond polar. In polar type of covalent bond and in the ionic bond, there is heterolytic type of cleavage when one atom gets the negative charge and the other gets the positive charge.

In $NaCl$ crystal when heterolytic cleavage happens sodium which is less electronegative gets the positive charge and shown as $N{a^ + }$ after the cleavage and chlorine gets the negative charge after the cleavage and shown as $C{l^ - }$ . Now if we take an example of covalent bond in a compound called chloroform $CHC{l_3}$ here we know that chlorine atoms are more electronegative as compared to hydrogen after heterolytic cleavage they break as follows.
$CHC{l_3}\,\, \to \,\,\,{H^ + }\,\, + \,\,CCl_3^ -$

Another type of cleavage is homolytic cleavage, in this type of cleavage bond to be broken are non-polar in nature that means there is no electronegativity difference. Let’s take an example for homolytic cleavage of chlorine gas $C{l_2}(g)$.

In this gas as both atoms are same and are of same electronegativity we get free radicals after the cleavage, $C{l_2}(g)\,\, \to \,\,2C{l^ \bullet }$

Any atom shown by a dot on its head is termed as free radical. Generally, homolytic cleavage happens when there are photochemical conditions given. But heterolytic cleavage normally happens in the presence of heat.
Note: Mainly the electronegativity difference decides the formation of a bond and also its breaking. Next point on which we have to keep an eye is the conditions given for the cleavage. In the branch of photochemistry where the reactions happen in the presence of sunlight happens by homolytic cleavage. Thermal reactions in which heterolytic cleavage happens normally take place when we give heat to the system.