Short answer
A molecule is a bonded group of atoms that acts as a unit. A compound contains atoms of at least two different elements in a defined composition. Water molecules are both; oxygen molecules are molecules but not compounds, and sodium chloride is a compound usually described as an ionic lattice rather than separate NaCl molecules. 1 2
Some molecules are compounds, but a molecule can contain one element and an ionic compound need not consist of discrete molecules.
On this page
At a glance
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| Question | Molecule | Compound |
|---|---|---|
| Key criterion | Discrete bonded unit | Different elements chemically combined |
| One element possible? | Yes, e.g. O₂ | No |
| Ionic lattice possible? | Not as discrete molecules | Yes |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Molecule. A discrete group of two or more atoms held together by chemical bonds. 1
Compound. A substance made from two or more elements chemically combined in a definite composition. 2
Key differences
These labels answer different questions. “Molecule” refers to a kind of particle; “compound” refers to a substance’s elemental composition. OpenStax distinguishes molecular substances from ionic compounds for this reason. 1 2
How to tell them apart
Ask whether the formula names a discrete bonded unit and whether it includes more than one element. O₂ is molecular but elemental. H₂O is a molecular compound. Solid NaCl is an ionic compound made of an extended lattice. 1 2
Where they overlap
Many common compounds, including water and carbon dioxide, are built from molecules. Both terms are useful in explaining chemical bonds and formulas. 1 2
Edge cases
Some covalent substances form extended networks rather than individual molecules; graphite and quartz require care. Formula units for ionic solids give ratios, not free-standing molecules in the crystal. 1 2
Why the distinction exists
Chemists separate particle structure from composition so a formula alone does not imply a particular arrangement of atoms. 1 2
Common misconceptions
Every compound is not a molecule, and every molecule is not a compound. The word “compound” does not require a little independent cluster. 1 2
Examples
An O₂ molecule contains only oxygen. An H₂O molecule contains two elements and is a compound. Table salt is a compound but forms an ionic crystal. 1 2
Sources
Sources checked October 3, 2026.
- OpenStax — Molecular and Ionic Compounds. Ions and ionic compounds.
- OpenStax — Phases and Classification of Matter. Elements and compounds.