Allotropy

Allotropy is the ability of a chemical element to exist in two or more structurally distinct forms in the same physical state. These forms are called allotropes.

Crystal structure: The ordered arrangement of atoms, ions, or molecules in a crystalline solid. Different atomic arrangements give solid allotropes distinct structures.
Diamond: A crystalline form of carbon in which each atom bonds to four neighbors in a rigid network. Its three-dimensional covalent network contrasts with carbon’s layered and molecular forms.
Oxygen: A chemical element with atomic number 8 that occurs as diatomic molecules and other forms. Its O₂ and O₃ forms are familiar gaseous allotropes.
Polymorphism: The ability of a solid substance to crystallize in more than one structure. Polymorphism concerns a substance’s crystal forms; allotropy concerns forms of an element.
Chemical bond: An attraction that holds atoms or ions together in a molecule or solid. Elements can form allotropes by changing how their atoms bond.
Graphite: A form of carbon made of sheets of bonded atoms, with weak attractions between sheets. Its layered structure shows how a different atomic arrangement changes material properties.
Ozone: A triatomic form of oxygen whose molecules contain three oxygen atoms. It differs from ordinary oxygen in molecular structure and chemical behavior.
Isomerism: The existence of compounds with the same molecular formula but different structures or arrangements. Isomerism usually distinguishes compounds, while allotropy distinguishes forms of an element.
Coordination number: The number of nearest neighboring atoms or ions around a selected atom in a structure. Different allotropes can give atoms different numbers of nearest neighbors.
Graphene: A single atomic layer of carbon atoms arranged in a hexagonal lattice. It isolates one of graphite’s sheets, linking a bulk allotrope to a two-dimensional material.

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