What does molecule mean?
A molecule is a group of atoms joined by chemical bonds. It is the smallest particle that remains electrically neutral while retaining the chemical properties of the substance it forms, making it a central concept in chemistry and molecular biology. A water molecule, for example, consists of one oxygen atom and two hydrogen atoms arranged in a distinctive bent shape. The word commonly appears in discussions of molecular structure, chemical reactions, pharmaceuticals, materials science, and biological processes. Although “molecule” is often used informally to mean a tiny part of anything, its strict scientific meaning requires atoms joined in a definite chemical relationship. The term also distinguishes molecules from atoms, which are the basic units of an element, and from ions, which carry an electrical charge.
nounA molecule is the smallest electrically neutral particle of a substance that retains its chemical identity and consists of two or more atoms held together by chemical bonds. In some specialized contexts, a molecule can consist of a single atom, especially when describing noble gases.
- A chemically bonded group of two or more atoms that forms the smallest neutral particle retaining a substance's chemical properties.
"The water molecule contains two hydrogen atoms covalently bonded to one oxygen atom."
"The molecule changes shape as the surrounding temperature rises."
"Researchers designed a molecule that can bind to a particular protein."
Molecules is the standard plural; the singular form is used for one molecular particle.
"The researchers isolated several molecules for further analysis."
Every drop of water you encounter is a crowded world of molecules, each one built from just two hydrogen atoms and one oxygen atom.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does molecule come from?
The word comes from Latin molecula, a diminutive of moles, meaning “a mass” or “a small portion.” The Latin word was borrowed into English during the 17th century, initially referring to a very small mass. Its modern chemical sense developed as the understanding of atoms and chemical combination became more precise. The related English word mole, now the name of a chemical amount unit, also reflects this history.
Related word forms
How molecule is actually used
The term is used primarily in chemistry and molecular science. In everyday speech, “molecule” may be used informally for a very small quantity or constituent part of a larger system, though this use is not chemically precise.
Easily confused with molecule
An atom is the smallest unit retaining an element's chemical properties, whereas a molecule generally consists of two or more atoms chemically bonded together.
A molecule is electrically neutral overall, while an ion carries a net positive or negative electrical charge.