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The term “resonance structure” refers to a collection of two or more Lewis Structures that together describe the electronic bonding of a single polyatomic species, including fractional bonds and charges. Resonance structures are capable of explaining delocalized electrons that cannot be described in an integer number of covalent bonds using a single Lewis formula.
The different structures are called resonance structures because they “resonate” with each other, implying that they are all equally acceptable representations of the molecule. The resonance structures are drawn with the same link lengths and angles, and the electrons are dispersed in the same way between the atoms. The electrons in a resonance structure participate in more than one covalent bond, and the electron pairs are shared between the atoms in diverse ways.
Even when formal charges are taken into account, the bonding of certain molecules or ions cannot always be described by a single Lewis structure. Resonance is a term used to describe delocalized electrons within specific compounds or polyatomic ions whose bonding cannot be represented using a single Lewis formula. Numerous contributing structures are used to depict a molecule or ion with such delocalized electrons (also called resonance structures or canonical forms).
The carbon atom is connected to two oxygen atoms in the first resonance structure. A dashed line indicates the double bond between the carbon and oxygen atoms. The carbon atom is connected to a single oxygen atom and a second carbon atom in the second resonance structure. A dashed line indicates the solitary link between the carbon and oxygen atoms. The carbon atom is connected to a single oxygen atom and a hydrogen atom in the third resonance structure. A dashed line indicates the solitary link between the carbon and oxygen atoms. The carbon atom is connected to a single oxygen atom and a chlorine atom in the fourth resonance structure. A dashed line indicates the solitary link between the carbon and oxygen atoms.
How to draw resonance structure of carbonate ion
As with ozone, the carbonate ion’s electronic structure cannot be explained by a single Lewis electron structure. Unlike O3, however, CO32- ‘s real structure is a composite of three resonance structures.
1. Due to the fact that carbon is the least electronegative element, it is positioned centrally:
2. Carbon has four valence electrons, each oxygen has six, and there are two more for the valence charge of two. This results in a total of 4 + (3*6) + 2 = 24 valence electrons.
3. Three bonding pairs between the oxygen and carbon atoms are formed using six electrons:
4. We evenly distribute the remaining 18 electrons across the three oxygen atoms by attaching three lone pairs to each and showing the 2 charge:
5. There are no remaining electrons for the centre atom.
6. Because the carbon atom only has six valence electrons at this point, we must employ one lone pair from an oxygen to build a carbon–oxygen double bond. However, in this scenario, there are three viable options:
As is the case with ozone, none of these structures precisely describes the bonding. Each anticipates the formation of one carbon–oxygen double bond and two carbon–oxygen single bonds, but all C–O bond lengths are identical experimentally. We can write the carbonate ion’s resonance structures (in this example, three of them) as follows:
The final structure is a combination of these three resonance structures.
To complete the octet on the central atom, one oxygen atom must form a double bond with carbon. However, all oxygen atoms are equal, thus the double bond can originate from any of the three atoms. This results in the formation of three carbonate ion resonance forms. We know that the real arrangement of electrons in the carbonate ion is the average of the three configurations since we can write three identical resonance patterns. Again, studies demonstrate that all three C–O bonds are identical.
CONCLUSION
Resonance arises when two or more Lewis structures with similar atom configurations but distinct electron distributions can be written. The real electron distribution (the resonance hybrid) is a weighted average of the distribution represented by the various Lewis structures (the resonance forms). Formal charges can be assigned to each atom in a Lewis structure by considering each bond as if one-half of the electrons were assigned to each atom. These fictitious formal charges serve as a guide for establishing the optimal Lewis structure. It is preferable to have a structure with formal charges as near to zero as possible.
