A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds. Depending on context, the term may or may not include ions which satisfy this criterion. Molecules form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.

Some key characteristics of molecules include:

• Structure: A molecule consists of an aggregation of atoms held together by valence forces. The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged.

• Types: Diatomic molecules contain two atoms that are chemically bonded. If the two atoms are identical, they compose a homonuclear diatomic molecule, while if the atoms are different, they make up a heteronuclear diatomic molecule. Molecules containing more than two atoms are termed polyatomic molecules.

• Weight: A molecules molecular weight is the sum of all its constituent atoms atomic weights.

Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the chemical bond.

Molecules can be visualized using molecular modeling software, with the three main models used being wire frame or stick, ball and stick, and spacefill (or CPK) .