Answer:
The following
are some of the important aspects of resonance:
(i) When a single Lewis structure cannot explain all the properties
of the molecule and the molecule is supposed to have many structures with
similar energy, position of nuclei, bonding and non-bonding pairs of electrons,
each of which can explain most of the properties of the molecule, the molecule
is said to have resonance. The actual structure is in between of all these
contributing structures and is called resonance hybrid and the different
structures are called canonical forms.
(ii) The molecule as such has a single definite structure which
cannot be depicted by a Lewis structure.
(iii) The resonance hybrid is more stable than any one of the
canonical forms, i.e., it has less energy.
(iv) The canonical forms do not have any real existence.
They are only imaginary. The resonance hybrid has only real
existence.
(v) It has been observed that a molecule which shows resonance
has greater heat of formation than the calculated heat of formation of most
stable canonical form. The difference is called resonance energy.
Higher the resonance energy, more stable will be the molecule.
Carbonate ion can be represented by the following
structures:
i.e., there are two single
bonds and one double bond between carbon and oxygen atoms, showing unequal
bonding.
However, it is observed in
experimental findings that all carbon and oxygen bonds are equivalent.
Therefore, the \[CO_{3}^{2-}\] ion is best described by a resonance hybrid of
the various canonical forms.
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