What is a molecule?

A molecule is an identifiable unit of two or more chemically bonded atoms. The kinds and numbers of atoms matter alongside their connections and three-dimensional arrangement. Water, oxygen and carbon dioxide are molecular substances. However, not all matter consists of separate molecules: ionic crystals and metals have different arrangements.

Composition and molecular geometry

1. Elemental molecules and compounds An O2 molecule contains two atoms of the same element. H2O contains two hydrogen atoms and one oxygen atom, making water a compound. Consequently, not every molecule is a compound. Compounds contain different elements chemically combined; simply mixing substances does not produce one. 2. Reading formulas A molecular formula gives atom types and counts. A structural formula shows their connections. Substances with the same molecular formula can have different connections, making them structural isomers. Their behavior may consequently differ. 3. Bonds and shape Covalent bonds involve electron density shared between atoms. Bond polarity and molecular geometry affect the overall charge distribution. Water’s bent shape contributes to its polarity: identifying its atoms alone does not explain all its properties.

How does molecular structure affect everyday life?

4. Intermolecular interactions Boiling, melting and dissolution depend on interactions between molecules as well as bonds within them. Hydrogen bonding is an important interaction between suitable groups of atoms. When water boils, bonds inside most water molecules remain intact while molecules move farther apart. 5. Molecules versus crystals Table salt contains an extended lattice of sodium and chloride ions. NaCl expresses their ratio rather than a separate molecule. Diamond is an extended covalent network. Small-particle diagrams therefore cannot be applied identically to every material. 6. Investigation and applications Spectroscopy and diffraction help reveal molecular structures. Materials, food and pharmaceutical research investigate connections between structure and properties. Assessing a molecule’s effects also requires considering its quantity, surroundings and interactions with other substances.