What Is a Molecule?

Definition of a Molecule Plus Examples

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Water molecules. Laguna Design / Getty Images

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.

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 compound. 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.

Learn more:

Types of Chemical Bonds
List of Diatomic Molecules

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Helmenstine, Anne Marie, Ph.D. "What Is a Molecule?" ThoughtCo, Apr. 6, 2017, thoughtco.com/what-is-a-molecule-definition-examples-608506. Helmenstine, Anne Marie, Ph.D. (2017, April 6). What Is a Molecule? Retrieved from https://www.thoughtco.com/what-is-a-molecule-definition-examples-608506 Helmenstine, Anne Marie, Ph.D. "What Is a Molecule?" ThoughtCo. https://www.thoughtco.com/what-is-a-molecule-definition-examples-608506 (accessed November 19, 2017).