21 Chemistry -- Chemical Bonding and Shapes of Molecules

Define resonance and resonating structures. Write the rules to indicate the phenomenon of resonance. Also write the characteristics of resonance.

Define resonance and resonating structures. Write the rules to indicate the phenomenon of resonance. Also write the characteristics of resonance.

Resonance is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by a single Lewis formula.

A molecule or ion with such delocalized electrons is represented by several resonance structures. Resonance structures represent different ways of placing electrons on the atoms in a molecule's Lewis dot structure. 

It is possible to write more than one equivalent resonance structure for a molecule or ion, the actual structure is the average of the resonance structures known as a resonance hybrid.

The conditions of resonating structure are:

  • same positions of atoms
  • same number of paired and unpaired electrons
  • almost equal energy

Characteristics of Resonance are: 

brings change in bond length (single bond< double bond)

gives the ides of bond order (for example in Benzene=3/2 =1.5)

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