What Is A Molecule?

A molecule can be roughly thought of as any group of atoms stuck together. Here you will learn some important details.

Subjects: Chemistry


Atoms, elements, molecules… What’s the difference? This is part 3 in the Stated Clearly series: An Introduction to Chemistry. In it you will find a simplified definition of a molecule, you will learn how we model molecules, and you will see actual images of real molecules and their vibrational modes!

About our definition of a molecule

In this video we describe a molecule as “a group of atoms stuck together, usually through chemical bonds”.

This definition is great because it’s so easy to make sense of, but there are some problems with it. Biologists will sometimes consider a double stranded chain of DNA to be a “single molecule”, even though each half of the strand is bound to the other via non-chemical hydrogen bonds. The same is true for some protein complexes composed of multiple sub-units.

Alternatively, some crystals such as quartz are made of repeating patterns of atoms all chemically bound. Using our definition, you’d have to consider an entire quartz crystal to be a “single molecule”. Chemists don’t usually do this, instead they consider each repeating sub-unit to be a molecule. Pure metals have a similar issue.

Language is a living, evolving mess! Even in formal scientific fields where you might expect more consistency.

About our depiction of hydrogen molecule formation

In this animation we show a hydrogen molecule forming in space via a collision of just two atoms. Normally this reaction also requires some sort of dust or ice particle to trap atoms as they bind together.

To avoid distraction when teaching the basic concept of a molecule we chose to ignore this technicality in the animation.

For Teachers

The content of this video meets criteria in the following Disciplinary Core Ideas defined by Next Generation Science Standards. Use our videos to supplement classroom curriculum.


Our videos benefit from guidance and advice provided by experts in science and education. This animation is the result of collaboration between the following scientists, educators, and our team of creatives.

  • Ara Apkarian, PhD
  • Venkat Bommisetty, PhD
  • Danielle Watt, PhD
  • Eric Potma, PhD
  • Joonhee Lee, PhD
  • Wilson Ho, PhD
  • Anthony Danzl
  • Jon Perry
  • Jordan Collver
  • Tyler Proctor