Is Helium Diatomic? Why?

No, helium is not diatomic. Helium is a monatomic gas, meaning that it exists as individual atoms rather than as molecules. Helium atoms do not bond with each other because their outermost electron shell is already full, consisting of two electrons. 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.

Why is helium monatomic?

Helium is a monatomic gas because it exists as single, individual atoms rather than molecules. Unlike most other gases, which consist of molecules made up of two or more atoms, helium atoms are chemically stable on their own and do not naturally bond with other atoms to form molecules.

This is because helium is a noble gas, which means it has a full outer electron shell and is therefore very stable and non-reactive. ²

Helium’s electron configuration is 1s², which means it has two electrons in its innermost shell and two electrons in its outermost shell, giving it a full valence shell. ³

This stable electron configuration makes it energetically unfavorable for helium atoms to form chemical bonds with other atoms.

Therefore, helium gas exists as individual, monatomic atoms that move freely and independently of one another. 

Helium’s monatomic nature also makes it a very good thermal conductor, as its atoms are free to move and transfer heat energy without being hindered by molecular bonds. ⁴

Does diatomic helium exist?

No, diatomic helium does not exist under normal conditions. Helium is a noble gas and has a full outer electron shell, making it very stable and unreactive. ⁵

This stable electron configuration makes it energetically unfavorable for helium atoms to form chemical bonds with other atoms, including other helium atoms. 

As a result, helium exists as a monatomic gas, with each atom existing independently of one another. 

Therefore, it is not possible for helium atoms to bond together to form diatomic molecules under normal conditions.

Is Helium written as He or He₂?

Helium is written as “He”, without a subscript of “2”. This is because helium is a monatomic element and does not naturally exist as a diatomic molecule under normal conditions. ⁶

The chemical symbol “He” represents a single helium atom, which is the stable and most common form of helium. 

The subscript “2” in a chemical formula represents two atoms of that element bonded together to form a molecule, but since helium does not naturally bond with itself, the subscript “2” is not used in its chemical formula.

Further reading

Is Lithium a Metal or Nonmetal?
Why is Boron a Metalloid?
Is Boron a Metal?
Is Boron a Nonmetal?
Why is Oxygen a Nonmetal? 

1. Monatomic gas – Wikipedia. (2016, June 6). Monatomic Gas – Wikipedia. https://en.wikipedia.org/wiki/Monatomic_gas
2. It’s Elemental – The Element Helium. (n.d.). It’s Elemental – the Element Helium. https://education.jlab.org/itselemental/ele002.html
3. Electron Configuration for Helium (He). (n.d.). Electron Configuration for Helium (He). https://terpconnect.umd.edu/~wbreslyn/chemistry/electron-configurations/configurationHelium.html
4. ALLEN, J. F., PEIERLS, R., & UDDIN, M. Z. (1937, July). Heat Conduction in Liquid Helium. Nature, 140(3532), 62–63. https://doi.org/10.1038/140062a0
5. Helium dimer – Wikipedia. (2015, February 9). Helium Dimer – Wikipedia. https://en.wikipedia.org/wiki/Helium_dimer
6. Lohr, L. L., & Blinder, S. M. (2007, May). The Weakest Link: Bonding between Helium Atoms. Journal of Chemical Education, 84(5), 860. https://doi.org/10.1021/ed084p860