What is a molecule?

What Is a Molecule?

The terms molecule, compound, and atom can be confusing! Here's an explanation of what a molecule is (and is not) with some examples of common molecules.
Answer: Molecules form when two or more atoms form chemical bonds with each other. It doesn't matter if the atoms are the same or are different from each other.

Examples of Molecules

Molecules may be simple or complex. Here are examples of common molecules:

• H₂O (water)
• N₂ (nitrogen)
• O₃ (ozone)
• CaO (calcium oxide)
• C₆H₁₂O₆ (glucose, a type of sugar)

Molecules Versus Compounds

Molecules made up of two or more elements are called compounds. Water, calcium oxide, and glucose are molecules that are compounds. All compounds are molecules; not all molecules are compounds.

What Is Not a Molecule?

Single atoms of elements are not molecules. A single oxygen, O, is not a molecule. When oxygen bonds to itself (e.g., O₂, O₃) or to another element (e.g., carbon dioxide or CO₂), molecules are formed.