Science glossary film: Molecular weight

The sum of the atomic masses of all the atoms in a molecule, usually expressed in atomic mass units. For a small molecule such as hydrogen, H₂, molecular weight will be a small number – two in this case. For a large organic or protein molecule it can run into the thousands or millions.

For a small molecule such as hydrogen, H₂, molecular weight will be a small number – two in this case. For a large organic or protein molecule it can run into the thousands or millions.