Ozone is oxygen in a triatomic state. Ozone is an allotrope of oxygen with the chemical formula 0₃.

Ozone is depicted as a resonance structure. Oxygen can form a double bond with itself to give diatomic oxygen. The triatomic molecule ozone contains one single bond and one such double bond. The location of these bonds constantly switches (i.e., resonates) between the two possible bond configurations.

The name ozone comes from the Greek Ozon meaning smell. At atmospheric temperatures, ozone is a colorless gas with an odor similar to chlorine that can usually be detected at a level of about 0.01 parts per million.

High in the atmosphere, ozone plays an important protective role by diminishing the amount of potentially damaging ultraviolet radiation reaching the Earth. In sufficient concentration, however, ozone is a poison that at lower atmospheric levels is a pollutant that can be damaging to health. Ozone is...