(i) The extraordinary stability of benzene molecule may be attributed to resonance in the molecule. In benzene, each of the 6 C atoms is sp2 hybridised with one p-orbital on each carbon atom left unhybridised. While 2 of the sp2 orbitals form bonds with 2 C-atoms, the third one is involved in bonding with hydrogen atom. Thus, 3 of the valencies of C are satisfied.
(ii) This leaves the unhybridised p-orbital containing 1 electron each for bonding. Each of these p-orbitals can overlap with the adjacent C atom and thus, results in bonding.
(iii) Since the probability for each π-orbital to overlap with either of the two immediate neighbours is equal. Therefore, it alternately does so.
(iv) Thus, the π electrons (in unhybridised p-orbitals) are no more localised between just 2 carbon atoms but these 6π electrons are shared or attracted by all the 6 carbon atoms.
(v) This increased attraction is the reason for the ‘extraordinary’ stability of the benzene molecule with 3 double bonds.
(vi) These 3 π-bonds are not localised but are spread over the entire molecule.