Science
What is Molecule?
A molecule is two or more atoms bonded together, acting as a single unit. Molecules are how atoms combine to form everything from the water you drink (H₂O) to the oxygen you breathe (O₂) and the sugars that fuel your body.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains molecule.
Key things to understand
- 1A molecule forms when atoms share electrons in chemical bonds.
- 2It can be two of the same atom (O₂, oxygen gas) or different atoms (H₂O, water).
- 3Which atoms it has and how they're arranged decide its properties — water and hydrogen peroxide share atoms but behave very differently.
- 4A compound is a molecule made of at least two different elements.
- 5Molecules range from tiny (two atoms) to enormous (a DNA molecule has billions).
Frequently asked questions
- What's the difference between a molecule and a compound?
- Every compound is a molecule, but not every molecule is a compound. A compound contains two or more different elements; O₂ is a molecule but not a compound because it's all one element.
- What holds a molecule together?
- Chemical bonds — most often atoms sharing electrons (covalent bonds) — hold a molecule's atoms together.
- What is the smallest molecule?
- Hydrogen gas (H₂), made of just two hydrogen atoms, is the smallest and lightest molecule.