What do you call a pair of atoms?

A pair of atoms is called a molecule. This term specifically refers to two or more atoms that are chemically bonded together, which can be the same type of atom or different types. For instance, a molecule can be as simple as two oxygen atoms bonded together to form O₂, or it can consist of different atoms, like in water (H₂O), which is made up of hydrogen and oxygen atoms.

While a compound refers to a substance formed when two or more different types of atoms are chemically bonded, this term does not apply to pairs of the same kind of atom, such as a diatomic molecule. An element is a pure substance made of only one type of atom, and an atom is the smallest unit of matter that retains the properties of an element. Hence, describing a pair of atoms specifically as a molecule accurately encompasses the idea of them being combined to form a new entity.