Bond fission

A covalent bond is formed when electrons are shared between two atoms. A single bond (sigma bond) is thus formed after sharing of two electrons. Now a chemical reaction takes place when old bonds are broken and new ones are created. There are two ways of breaking a bond as shown below.

Homolytic fission

Figure 1. Homolysis

Homolytic fission is the type of fission in which electrons are equally shared after breaking of covalently bonded atom having same electro negativity. After this type of bond breaking free radical is formed and usually for this purpose light particles or photons is needed. Free radicals are the species of odd electron.

Heterolytic fission

Figure 2. Heterolysis

Heterolytic fission is the type of fission in which electrons are unequally shared after breaking of polar covalently bonded atom having different electro negativity. After this type of bond breaking carbocation (positively charged species) or carbanion (negatively charged species) is formed and usually for these purpose reagents (electrophiles or nucleophiles) is needed.