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.
with chlorine (especially fluoride) reaction may occur very rapidly.To prevent explosion, halogen preferably mixed with nitrogen.
Similar reactions occur with fluorine, chlorine and bromine;iodine, although it is also halogen, they do not go.