Consider one of the varieties of chemical chain reactions - halogenation of saturated hydrocarbons (alkanes).Take for example, the simplest hydrocarbon - methane.Its formula CH4.How is the chlorination of methane?
First of all, you need to initiate the process.Under the action of ultraviolet radiation, the molecule breaks up into atoms of chlorine: Cl2 = Cl.+ Cl.
atomic chlorine is extremely chemically active, it immediately "attacked" molecule hydrocarbon,
"selecting" her electron, by which completes the electronic level to its steady state.But the result is a another radical CH3, which immediately reacts with the molecule Cl2, forming a molecule of chloromethane SN3Sl and atomic radical Cl.The general scheme of this step: CH4 + Cl2 = CH3Cl + HCl.
Accordingly, the molecule is exposed to chloromethane instantly "attack" of the atomic chlorine, which "selects" the second electron from the hydrogen atom.As a result, again formed hydrocarbyl.And that reacts with another molecule of chlorine, and the obtained molecule dichloromethane, or dichloromethane and hydrogen chloride: CH3Cl3 + Cl2 + HCl = CH2Cl2.
In exactly the same way is the subsequent stage of the reaction, resulting from dichloromethane (methylene chloride) is formed trichloromethane (chloroform): CHCl3.
And the last stage - the formation of chloroform, carbon tetrachloride (or carbon tetrachloride) CCl4.The reaction is complete when the chlorine atom can no longer displace the hydrogen atoms, taking their place.