A discrete assembly of two or more atoms held together by chemical bonds that behaves as an independent chemical species.

Principle

Chemical bonds—covalent, ionic, coordinate, metallic, and weaker intermolecular forces—determine the stability, geometry, and emergent properties of a molecule; electronic structure and molecular orbitals explain reactivity and spectra.

Demonstration

A water molecule consists of two hydrogen atoms covalently bonded to one oxygen atom in a bent geometry; its polar bonds and overall dipole explain solvent behavior and hydrogen bonding.

Misapplication

Calling an extended ionic lattice or network solid a 'molecule' (for example treating crystalline sodium chloride as discrete NaCl molecules) or ignoring that some assemblies are supramolecular complexes rather than single covalently bound molecules.

Consequence

Identifying molecular composition and structure enables prediction of reactivity, physical properties, and spectroscopic signatures, and guides synthesis and functional design in chemistry and biology.

Reversal

A single atom or an infinite periodic solid (network covalent or ionic lattice) that lacks a well-defined discrete molecular unit.

Boundary

Applies to discrete bonded assemblies of atoms (neutral or charged) considered as single chemical entities; excludes truly extended solids without discrete molecular units and purely physical aggregates lacking defined bonding topology.

Semantic Tension

Tension between molecule and supramolecular assembly, and between molecular description and band/solid-state descriptions where electronic delocalization makes single-molecule concept less useful.

Synthesis

A molecule is a stable assembly of atoms connected by defined bonding interactions whose electronic structure and geometry determine its distinct chemical identity, properties, and reactivity, distinct from single atoms and extended solids.