In this post we will try to find out the correct structure and right way to represent the fractional bond of (CO3)-2ion. When we draw Kekulé structure of (CO3)-2 ion, we show double bond between C and O atom and single bonds in between C and O-ion. But in MOT we discovered that the bonds between C and O are neither double nor single; instead, their bond order is 1(1/3)
In MOT we have seen that the pi bond is delocalised over all atoms. Here all O atoms demonstrate their comradeship and one by one share the negative charge and pi bond as well. Let’s see how.
These structures don’t exist separately but they contribute to form the actual structure. The real structure is a combination of all these structures. These structures all called resonating structures and they combine to form a resonance hybrid which represents the actual structure. This phenomenon of delocalisation of charge and pi bond is known as resonance.
These structures don’t exist separately but they contribute to form the actual structure. The real structure is a combination of all these structures. These structures all called resonating structures and they combine to form a resonance hybrid which represents the actual structure. This phenomenon of delocalisation of charge and pi bond is known as resonance.
Resonance has a great significance in stability of a number of molecules like (NO3)- ion which has bond order 1(1/3) and (NO2)- ion which has bond order 1.5.
Resonance plays an important role in determining the stability of Benzene (C6H6). In the whole aromatic chemistry we study Benzene and its derivatives. Stability of Benzene was a big question because it is a cyclic molecule and has 3 double bonds. It is expected to be 1(1/2) very unstable because of the above mentioned qualities. MOT determines its bond order to be , that means double bonds are delocalised over all the 6 C atoms.
The higher number of resonating structures gives extra stability to Benzene molecule. In resonating hybrid you can see 3 delocalised pi bonds which are represented by rings above and below the plane hexagon.
You have learned about ionic and covalent bonds. But if you try to guess the bonding in O3 molecule you need a third type of bond covalent co-ordinate bond. In the next post we will discuss it in detail.
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