Why is Oxygen Diatomic? (+ 3 Fascinating Facts to Know)

Oxygen is a diatomic molecule. At standard temperature and pressure (STP), oxygen exists as a gas composed of diatomic molecules, each consisting of two oxygen atoms bonded together by a covalent bond. The chemical formula for this diatomic molecule of oxygen is O₂. ¹

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Explanation: Why is oxygen a diatomic molecule?

Oxygen is a diatomic molecule because it is more stable when it exists as two atoms bonded together in a molecule, rather than as individual atoms.

Oxygen is a highly reactive element and has a strong tendency to form chemical bonds with other elements. Each oxygen atom has six valence electrons in its outermost shell, which means that it needs two additional electrons to fill its outer shell and become stable. ^{2 3}

By sharing two electrons with another oxygen atom, both atoms can complete their outer shells and form a stable molecule.

The O-O bond in oxygen is a double bond, which means that two pairs of electrons are shared between the two atoms. ⁴ This results in a stable molecule of O2, which is the form of oxygen that is most commonly found in the Earth’s atmosphere.

Therefore, oxygen is a diatomic molecule because the O2 molecule is more stable than individual oxygen atoms, and the double bond between the two atoms allows them to achieve a stable configuration with filled outer shells.

Does monatomic oxygen exist?

Yes, monatomic oxygen (O) does exist, but it is relatively unstable and reactive. Monatomic oxygen is an intermediate in several chemical reactions involving oxygen, and it is also produced in some high-temperature processes such as combustion and high-energy radiation. ^{5 6}

Monatomic oxygen can be generated in the laboratory by various methods, such as by dissociating O2 molecules using ultraviolet radiation or electric discharges. However, monatomic oxygen is highly reactive and tends to react quickly with other molecules to form more stable compounds. ⁷

For example, when monatomic oxygen comes into contact with water vapor, it can react to form hydrogen peroxide (H2O2), which is a stable compound. ⁸

In nature, monatomic oxygen is not typically found in significant quantities because it quickly reacts with other molecules to form more stable compounds.

However, it is an important intermediate in many atmospheric processes, such as the production of ozone in the Earth’s atmosphere and the breakdown of pollutants such as nitrogen oxides.

How do oxygen atoms bond to form a diatomic molecule?

Oxygen atoms bond to form a diatomic molecule by sharing two electrons through a double covalent bond. Each oxygen atom has six valence electrons in its outermost shell and requires two additional electrons to fill its outer shell and become stable. 

When two oxygen atoms approach each other, they can share two electrons, which creates a double bond between them. This double bond allows both oxygen atoms to achieve a stable electron configuration, with eight electrons in their outermost shell, similar to the noble gas neon. 

The attraction between the positively charged nuclei of the two oxygen atoms and the negatively charged electrons shared in the bond holds the two atoms together in the O2 molecule.

This process results in the formation of a stable diatomic molecule of oxygen, which is the most common form of oxygen found in the atmosphere. ⁹

Further reading

Is Sulfur Diatomic?
Why is Iodine Diatomic?
Why is Chlorine Diatomic?
Is Nitrogen a Compound?
Is Oxygen a Compound? 

1. Molecular oxygen – Energy Education. (n.d.). Molecular Oxygen – Energy Education. https://energyeducation.ca/encyclopedia/Molecular_oxygen
2. Switching oxygen molecules between a reactive and unreactive state. (n.d.). Switching Oxygen Molecules Between a Reactive and Unreactive State. https://phys.org/news/2017-03-oxygen-molecules-reactive-unreactive-state.html
3. Reactions of Main Group Elements with Oxygen. (2013, October 2). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Main_Group_Reactions/Reactions_of_Main_Group_Elements_with_Oxygen
4. Lewis Structure for O2 (Dioxygen or Oxygen Gas). (n.d.). Lewis Structure for O2 (Dioxygen or Oxygen Gas). https://terpconnect.umd.edu/~wbreslyn/chemistry/Lewis-Structures/lewis-structure-for-O2.html
5. P. (n.d.). Atomic oxygen. Atomic Oxygen | O | CID 159832 – PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/159832
6. NASA – Out of Thin Air. (2011, February 17). NASA – Out of Thin Air. https://www.nasa.gov/topics/technology/features/atomic_oxygen.html
7. Johnston, H. L., & Walker, M. K. (1933, January). The Dissociation of Oxygen to 5000°K. The Free Energy of Atomic Oxygen1. Journal of the American Chemical Society, 55(1), 187–193. https://doi.org/10.1021/ja01328a019
8. Stanford scientists find water can transform into hydrogen peroxide when condensing on cold surfaces. (n.d.). Stanford Scientists Find Water Can Transform Into Hydrogen Peroxide When Condensing on Cold Surfaces. https://news.stanford.edu/press-releases/2020/11/23/cooled-water-vapydrogen-peroxide/
9. Boudreaux, K. A. (n.d.). The Parts of the Periodic Table. The Parts of the Periodic Table. https://www.angelo.edu/faculty/kboudrea/periodic/periodic_main6.htm