Inorganic Chemistry - First Class .….. (2017-2018) .… Second Course
1
It is often observed that a single Lewis structure is inadequate for the
representation of a molecule in conformity with its experimentally
determined parameters. For example, the ozone, O3 molecule can be
equally represented by the structures I and II shown below:
Resonance in the O3 molecule
*(structures I and II represent the two canonical forms while the structure
III is the resonance hybrid).
According to the concept of resonance, whenever a single Lewis structure
cannot describe a molecule accurately, a number of structures with
similar energy, positions of nuclei, bonding and non-bonding pairs of
electrons are taken as the canonical structures of the hybrid which
describes the molecule accurately. Thus for O3, the two structures shown
above constitute the canonical structures or resonance structures and their
hybrid, the III structure represents the structure of O3 more accurately.
This is also called resonance hybrid. Resonance is represented by a
double headed arrow.
* Some of the other examples of resonance structures are provided by the
carbonate ion and the carbon dioxide molecule.
