Delocalization of Electrons: Resonance and Its Applications
What Is Resonance?
Definition
Resonance
Resonance arises from the delocalization of electrons, where electrons are not confined to a single bond or atom but are spread across multiple atoms in a molecule.
The Basics of Delocalization
- In most covalent bonds, electrons are localized between two atoms.
- However, in some molecules, electrons can be delocalized, meaning they are shared across more than two atoms.
- This occurs when there are multiple valid ways to position double or triple bonds while still satisfying the rules of chemical bonding.
- When this happens, no single Lewis structure can accurately describe the molecule. Instead, the molecule is represented by resonance structures.
Definition
Resonance structures
Resonance structures are alternative Lewis structures showing different possible arrangements of bonds and lone pairs.
The actual molecule exists as a resonance hybrid, which is a blend of all the resonance structures.Note
- Resonance structures are not physical forms of a molecule flipping back and forth.
- They are a way of representing the delocalized nature of electrons.
Ozone ($O_3$)
- Ozone consists of three oxygen atoms.
- Its Lewis structures suggest two possible arrangements for the double bond and lone pairs:
- A double bond between the first and second oxygen atoms, with a single bond between the second and third.
- A double bond between the second and third oxygen atoms, with a single bond between the first and second.
- These two resonance structures can be represented as:$$
\text{O=O-O ↔ O-O=O}
$$ - Experimental evidence shows that both $O–O$ bonds in ozone are identical in length and strength, intermediate between a single bond and a double bond.
- This indicates that the electrons in the double bond are delocalized across the entire molecule.
