What is the structural formula for ozone?

Ozone Resonance Hybridization Structures

In order for the central oxygen atom to have an octet (8) electrons, there needs to be one single-bonded O atom and one double-bonded O atom. Typically a double bond is shorter than a single bond, however, experimental evidence indicates that both of the #"O-O"# and #"O=O"# bonds are the same length and the central O atom has an #sp^2# hybridization. In order to accommodate this, the ozone molecule is written so that the double bond is on one side and the single bond is on the other and then the other diagram is a mirror image. A double arrow is written between them to show that the structure is not exactly as it is shown, but is a resonance structure.

The diagram below shows the bond length for both #"O-O"# bonds is the same. The diagram on the left is another way to write the resonance structure of ozone. Instead of drawing a double bond on one side and a single bond on the other side and its mirror image, we draw one single bond for both and a dashed line under the single bond to indicate that it is a resonance structure and both of its bond lengths are the same.