If a pure [[element]] can form several physically and chemically different substances, it can form '''allotropes'''. The most famous is [[carbon]], which has four allotropes, although [[phosphorus]], [[oxygen]], [[sulphur]], and [[plutonium]] can also form allotropes (3,3,4, and 7 respectively). | If a pure [[element]] can form several physically and chemically different substances, it can form '''allotropes'''. The most famous is [[carbon]], which has four allotropes, although [[phosphorus]], [[oxygen]], [[sulphur]], and [[plutonium]] can also form allotropes (3,3,4, and 7 respectively). |