What is a Diatomic Element? – Definition & Examples

Diatomic elements are very unique compounds because they contain two atoms. Explore this lesson to learn about diatomic elements. Understand what they are, discovering the several different examples of them along the way.
What Is a Diatomic Element?
If you study the composition of earth, you will see there are major components that make up the earth’s atmosphere: nitrogen, oxygen and even a tad bit of argon. To be more specific, nitrogen makes up 78% of the atmosphere while oxygen makes up 21%. This oxygen, O2, and nitrogen, N2, have something in common: both are called diatomic elements.

As pure elements, diatomic elements are seven unique molecules that are composed of two atoms. All of the elements in this elite group are gases. If we look at the prefix ‘di-‘ in the word diatomic, it comes from the Greek origin of ‘two.’ One great way to know you are working with a diatomic element is to consider its formula. Every molecule has its own unique molecular formula, and for diatomic elements, their formula always contains a subscript of 2, which represents two atoms in its structure. As an example, the diatomic element oxygen has a formula of O2, meaning there are two separate oxygen atoms present.

Formation of Diatomic Elements
At room temperature, there are five diatomic elements, all of which exist in the gas form: hydrogen, nitrogen, oxygen, fluorine, and chlorine. If the temperature is raised slightly higher, two additional elements will be present: bromine and iodine. At room temperature, bromine and iodine commonly exist in the liquid form. However, with that higher temperature they will also exist as gases.

Diatomic elements are special as the atoms that form it do not like to be alone. That is, you will never find a nitrogen or fluorine atom, for example, hanging out solo. Rather, these atoms will always be paired together because they need to pool resources to have enough electrons. One great way to remember which atoms form the lucky seven diatomic elements is to think of the following mnemonic device: I Bring Cookies For Our New Home.

Useful Way To Remember The Seven Diatomic Elements
diatomic elements
If there is ever a need to identify these diatomic elements on the periodic table, they can be spotted by remembering the ‘seven rule’ as well. Shown in the illustration, if you take your finger and draw the number seven, starting at nitrogen, you will see that six of the diatomic elements are arranged in the shape of a number seven. When drawing the number seven don’t forget about the seventh element, hydrogen.

Location of diatomic elements on the Periodic Table.
periodic table
Looking at the molecular geometry of diatomic elements, they are classified as linear. Molecular geometry refers to the three dimensional shape of a compound. For example, diatomic chlorine has two chlorine atoms bonded together, and they are not bent at all. Instead, they look like a straight line.

Molecular Geometry of Diatomic Chlorine
diatomic chlorine