Molecule: definition in chemistry
Molecule: A group of two or more atoms held together by covalent bonds, such as O₂ or H₂O. It is the smallest unit of a covalent substance that keeps its chemical properties.
Molecules can be made of atoms of one element, such as O₂ and N₂, or of different elements, in which case they are also compounds, such as H₂O and CO₂. Ionic compounds like sodium chloride are not made of molecules but of a continuous lattice of ions. The shape of a molecule, set by its bonds and lone pairs of electrons, affects properties such as polarity and boiling point.
Examples
- Oxygen (O₂) — two oxygen atoms
- Water (H₂O) — a bent molecule
- Methane (CH₄) — a tetrahedral molecule
- Glucose (C₆H₁₂O₆) — 24 atoms in one molecule
On the periodic table
Molecules form mainly between nonmetals, found at the upper right of the table, which share electrons rather than transferring them.