A molecule made up of two atoms is called a diatomic molecule. The atoms can be from the same element or different elements. A diatomic molecule has a linear geometry, meaning the atoms are connected in a straight line. Almost all diatomic molecules are gases at room temperature ^[1-4].

Types of Diatomic Molecules

There are two types of diatomic molecules – homonuclear and heteronuclear ^[1-4].

Homonuclear

A diatomic molecule is said to be homonuclear if the two atoms are the same type. It takes form A₂. The subscript 2 indicates that two atoms have combined to form the molecule through a covalent bond. The covalent bond is always nonpolar and can be single, double, or triple. A homonuclear diatomic molecule is also known as a diatomic element. There are seven of them in the periodic table.

Examples

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Fluorine (F₂)
• Chlorine (Cl₂)
• Bromine (Br₂)
• Iodine (I₂)

All but bromine and iodine are gases at room temperature. Br₂ is liquid, and I₂ is solid at room temperature.

How to Remember the Diatomic Elements

All seven diatomic elements are nonmetals and end with ‘gen’. Hydrogen, nitrogen, and oxygen end with ‘gen’; the remaining four are halogens. An easy-to-remember mnemonic for the diatomic elements is: Have No Fear Of Ice Cold Beer.

Heteronuclear

A diatomic molecule is heteronuclear if the two atoms are of different types. The form of this molecule is A-B. Here, at least one of the atoms is a nonmetal. The bonding in a heteronuclear diatomic molecule is either covalent or coordinate covalent.

Examples

• Carbon monoxide (CO)
• Nitric oxide (NO)
• Hydrogen fluoride (HF)
• Hydrogen chloride (HCl)
• Hydrogen bromide (HBr)