The Diatomic Elements

The periodic table has several diatomic elements, sometimes known as “molecular elements”. Let’s learn what they are, and how they are different from diatomic molecules.

What are the 7 Diatomic Elements?

The 7 diatomic elements, which exist in nature as molecular elements, are listed below. More detailed information on each is provided in the following sections.

List of Diatomic Elements

  • Hydrogen (H2)
  • Nitrogen (N2)
  • Fluorine (F2)
  • Oxygen (O2)
  • Iodine (I2)
  • Bromine (Br2)
  • Chlorine (Cl2)
Periodic table with the diatomic elements highlighted in blue
Periodic table with the diatomic elements highlighted in blue

What is a Diatomic Element?

A diatomic element is a molecule composed of two of the same atom. The word diatomic comes from ‘di’ meaning two, and ‘atomic’ meaning atom. A monatomic element is stable with just one atom.

These diatomic elements are most stable in this paired form because it allows them to follow the octet rule. This means that generally there are not single atoms of oxygen or chlorine floating around. Instead, they are in the form of F2 or O2, the diatomic element or molecular element form.

Dot structure of bromine, a diatomic molecule
Bromine is one of the seven diatomic molecules

Sometimes diatomic elements are also referred to as homonuclear diatomic molecules. The homonuclear part means that both atoms in the molecule are the same.

Even though there are only 7, they are NOT rare! In fact, they are some of the most common elements in our atmosphere. The air around us is 21% oxygen (O2) and 78% nitrogen (N2).

There may be other atoms that temporarily form a diatomic element. However, they are not stable in this state and last for a very short amount of time. Therefore they are not considered one of the seven diatomic elements.

What is a Diatomic Molecule?

A diatomic molecule is a molecule that has two atoms, but the atoms can be different. For example, carbon monoxide (CO) is a diatomic molecule, but NOT a diatomic element. Another example of a diatomic molecule would be nitric oxide (NO).

Lewis dot structure of carbon monoxide or CO, a diatomic molecule
Carbon monoxide (CO), shown here, is a diatomic molecule but NOT a diatomic element

Therefore, our diatomic elements are also diatomic molecules. However, not all diatomic molecules are diatomic elements.

A diatomic molecule with two different atoms is also referred to as heteronuclear. Heteronuclear means the two atoms are different.

How to Remember the Diatomic Elements

There are several techniques to remember which elements are diatomic. First off, there are some commonalities between the diatomic elements.

  • One is that they are all non-metal. None of the metal elements are diatomic.
  •  Second, the non-halogen diatomic elements all end with ‘-gen’. The halogen group also ends with ‘-gen’.

Another technique is to memorize the shape of the elements on the periodic table (image below). All the elements are bordering on each other except for hydrogen in the standard periodic table layout. They also form an upside-down ‘L’ shape.

Finally, there are many sayings to remember the first letter of all the elements. An intuitive order is to start with hydrogen, then go across the periodic table, and then down the halogens. This makes it easy to match the letter to the element. Several example sayings are listed below or you can make up your own!

 Have No Fear Of Ice Cold Beverages

(Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine)

A second and third option:

He Needed Oxygen For Controlling Both Insects.

(Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine)

I Have No Cats Breaking Famous Opals

(Iodine, Hydrogen, Nitrogen, Chlorine, Bromine, Fluorine, Oxygen)

Some people also use the word ‘BrIClHOF’  (pronounced brinkle-hoff) which incorporates the chemical symbol of each element.

Diatomic Halogen Elements

Lewis dot structure of chlorine, a diatomic element

Four diatomic elements are halogens—Cl2, F2, Br2, I2. The halogen elements have a single bond between the two atoms. Fluorine and chlorine are gasses at room temperature. Bromine is always a liquid. Iodine can be either a liquid or a solid depending on temperature, pressure, and other factors.

Diatomic Element- Nitrogen

Lewis dot structure of N2 nitrogen

Nitrogen is a diatomic element that is a gas at room temperature. Nitrogen is critical on earth. It is the most abundant element in our atmosphere. Additionally, it is found in all living organisms.

Diatomic Element- Oxygen

Lewis dot structure of oxygen O2

Oxygen is a diatomic element that is a gas at room temperature. Oxygen is a colorless and odorless gas. A large percentage of our atmosphere is oxygen, and it plays a vital role in sustaining life on earth!

Diatomic Element Hydrogen

Diatomic element hydrogen dot structure

Hydrogen is a diatomic element that is colorless and odorless gas at room temperature. Hydrogen has been proposed as an alternative fuel that is more environmentally friendly.