Britannica Sources used in this answer

What are the two main allotropes of oxygen?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — oxygen group element Modern version of the periodic table of the elements (printable).

The two main allotropes of oxygen are:

Diatomic oxygen ( $O_{2}$ ): This is the most stable form of the element under ordinary conditions.12
Triatomic oxygen (ozone, $O_{3}$ ): This form is less stable than diatomic oxygen and is characterized by its pungent odor and powerful oxidizing properties.123

While there is some evidence for a highly unstable tetratomic species ( $O_{4}$ ), diatomic and triatomic oxygen are recognized as the primary allotropic forms.13