A group of atoms can remain bound to each other, forming a molecule. A molecule is electrically neutral. It need at least two atoms held together by covalent chemical bonds. A molecule may consist of atoms of a single chemical element, as with oxygen (O2), or of different elements, as with water (H2O).
Molacules make up most of the oceans and atmosphere, crust, mantle, and core of the Earth. Some may contain many chemical bonds, but are not made of identifiable molecules. Ionic crystals like salts and covalent crystals called network solids, often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond or sodium chloride).
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