Allotrope

An allotrope is one of two or more structurally distinct forms of the same chemical element in the same physical state. Different atomic arrangements or bonding give allotropes distinct properties.

Chemical element: A pure substance whose atoms have the same number of protons. All allotropes preserve the element’s identity by keeping the same proton number.
Diamond: A crystalline form of carbon in which each atom bonds tetrahedrally to four others. Diamond is a hard carbon allotrope built from a three-dimensional covalent network.
Phase transition: A transformation between distinct physical states or phases of matter. Some allotrope changes accompany a change in crystal phase while the element remains solid.
Semiconductor: A material whose electrical conductivity lies between that of a conductor and an insulator and can be controlled. Semiconducting carbon forms such as graphene invite comparison with other allotropes’ electrical behavior.
Isomer: One of two or more compounds with the same molecular formula but different arrangements of atoms. Isomers vary the structure of a compound; allotropes vary the structure of an element.
Chemical bond: An attraction that holds atoms or ions together in a substance. Different bonding arrangements can produce distinct forms of the same element.
Graphite: A form of carbon composed of layers of hexagonally bonded atoms. Its layered structure makes graphite a contrasting solid allotrope of carbon.
Polymorphism: The ability of a solid material to crystallize in more than one structure. Polymorphism describes a related structural phenomenon, often used for compounds rather than elements.
Electrical conductivity: A measure of how readily a material carries electric current. Allotropes of carbon differ greatly in conductivity because their bonding structures differ.
Isotope: One of multiple forms of an element whose atoms have different numbers of neutrons. Isotopes differ in nuclear composition, whereas allotropes differ in atomic arrangement or bonding.

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