Summary of bond polarisation and fission

A homoatomic bond exists between identical atoms. In such a case the bond is unpolarised, because the electrons are equally shared, and so there is no permanent charge separation. 

For most purposes the induced polarisation of the H-C bond can be ignored, while in H-O, H-F and H-Cl bonds it is significant. One consequence of this polarisation is that lone pairs can interact with the 8+ hydrogens by forming a hydrogen bond, which is a weak Coulombic interaction. This bond can be either intermolecular or intramolecular. 

When a carbon atom is bonded to oxygen, nitrogen or chlorine, it forms the positive end of the bond. In contrast, if it is bonded to a metal, it forms the negative end of the bond. 

The induced polarisations within a molecule can be summed together as vectors, to give the overall dipolar motion of the molecule. For some molecules, like methane and boron trichloride, the result is zero while for others, like water and ammonia, the result is non-zero. 

Homoatomic bonds tend to prefer homolytic bond fission, which results in radicals being formed while heteroatomic bonds often undergo heterolytic bond fission, which results in ions being formed. 

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