Allotrope: definition in chemistry
Allotrope: One of two or more different forms of the same element in the same physical state, with the atoms bonded or arranged differently.
Allotropes contain the same kind of atom but can have very different properties, because properties depend on how the atoms are joined. Diamond and graphite are both pure carbon, yet diamond is the hardest natural material and an electrical insulator, while graphite is soft, slippery and conducts electricity. Some elements change from one allotrope to another at a particular temperature or pressure. The term applies only to elements; different crystal forms of a compound are called polymorphs.
Examples
- Carbon — diamond, graphite, graphene and fullerenes such as C₆₀
- Oxygen — ordinary O₂ and ozone (O₃)
- Phosphorus — white, which ignites in air, and the much safer red
- Tin — shiny white tin slowly turns into crumbly gray tin below 13 °C
On the periodic table
Allotropes are especially common in groups 14 to 16, among elements such as carbon, tin, phosphorus, sulfur and selenium.