Final answer:
Resonance is a way of describing bonding in molecules and ions by combining different contributing structures. Resonance structures help represent molecules or ions that cannot be correctly described by a single Lewis structure.
Step-by-step explanation:
Resonance is a way of describing bonding in molecules and ions by a combination of contributing structures into the actual structure. The hybrid of the contributing structures, called a resonance hybrid, represents the overall delocalization of electrons within the molecule or ion. When a molecule or ion cannot be correctly represented by a single Lewis structure, resonance structures are used to depict the different possible arrangements of electrons.
For example, ozone (O3) is an example of a molecule that cannot be represented by a single Lewis structure. It is best described by multiple resonance structures, where the double bond is delocalized between the oxygen atoms, creating an average of one-and-a-half bonds between each oxygen atom.
Resonance structures are indicated by a double-headed arrow and are used to show the different possibilities of electron arrangement within the molecule or ion.