Initiation : The chlorination of methane follows a free radical mechanism. Initially, by the action of heat or sunlight on Cl2, the Cl – Cl bond breaks. $\mathrm{Cl}-\overset{\underset{↻}{↷}}{\mathrm{Cl}}$ → $\overset{.}{\mathrm{Cl}}+\overset{.}{\mathrm{Cl}}$ Propagation : This produces two free radicals which abstract a hydrogen free radical from the methane molecule thereby generating a methyl free radical. $\overset{.}{\mathrm{Cl}} + \mathrm{H}-\overset{\underset{↺}{↶}}{\mathrm{CH}_3}$ → $\mathrm{H-Cl}+\overset{\bullet}{\mathrm{CH}_3}\ \text{methyl radical}.$ Termination : Now this methyl free radical may either combine with a chlorine free radical to form the desired product – chloromethane or may combine with another methyl radical to form an ethane molecule. $\overset{.}{\mathrm{CH}_3}+\overset{.}{\mathrm{Cl}}$ → $\underset{\text{methyl chloride}}{\mathrm{CH}_3\mathrm{Cl}}$ or $\overset{.}{\mathrm{CH}_3}+\overset{.}{\mathrm{CH}_3}$ → $\underset{\text{ehtane}}{\mathrm{CH}_3-\mathrm{CH}_3}$ This is how ethane is generated during the chlorination of methane.