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Molecule

MOL-uh-kyool /ˈmɒlɪkjuːl/

nounB2SATTOEFL

generaltechnical

A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

Molecules can be simple (like O2) or complex (like DNA). They are distinct from individual atoms and from ions (charged atoms/molecules).

The story behind the word. The word 'molecule' comes from the French 'molécule,' which itself is a diminutive of the Latin 'moles,' meaning 'mass' or 'heap.' The suffix '-cule' is a diminutive, so 'molecule' literally means 'a small mass.' The term was first used in the mid-18th century to describe the smallest particles of a substance, eventually solidifying into its modern chemical meaning by the early 19th century.

Word relationships

particle: More general; a molecule is a specific type of particle.
unit: Can refer to any fundamental quantity; 'molecule' is a specific chemical unit.

atom: An atom is a single, indivisible unit of an element; a molecule is a group of atoms bonded together.

Commonly confused with

Atom: An atom is the smallest unit of an element; a molecule is a group of two or more atoms chemically bonded.

Word family

molecular (adjective): relating to or consisting of molecules
molecularity (noun): the number of molecules involved in a reaction

Collocations

water molecule
gas molecule
organic molecule
polar molecule
molecular structure

Example sentences

"Each water molecule consists of two hydrogen atoms bonded to one oxygen atom." Water is composed of individual H2O molecules.
"Oxygen molecules are essential for respiration in most living organisms." The air we breathe is a mixture of various gas molecules, primarily nitrogen and oxygen.
"Understanding the precise shape of a drug molecule is crucial for predicting its interaction with biological targets." Scientists use powerful microscopes to visualize the arrangement of atoms within a molecule.

Memory hook

Think 'MOL-d' (a small shape) and 'MOL-ecule' (a small, fundamental shape of matter). Smallest chemical unit.

When not to use

Do not use 'molecule' for individual atoms or for ionic compounds that form crystal lattices rather than discrete molecular units (e.g., NaCl is a formula unit, not a molecule, in its solid state).

Fun facts

The existence of molecules was a subject of debate for centuries, only definitively proven in the early 20th century.
The concept of a 'mole' in chemistry (Avogadro's number) is directly related to counting the vast number of molecules in a given substance.