What are allotropes? Give an example.

Allotropes are different forms of the same element. Different bonding arrangements between atoms result in different structures with different chemical and physical properties. Allotropes occur only with certain elements, in Groups 13 through 16 in the Periodic Table.

An allotrope is a variant of a substance consisting of only one type of atom. It is a new molecular configuration, with new physical properties. Substances that have allotropes include carbon, oxygen, sulfur, and phosphorous. Allotropes of a given substance will often have substantial differences between each other. For example, one allotrope of carbon, fullerene, is many times stronger and lighter than steel. An allotrope should not be confused with phase, which is a change in the way molecules relate to each other, not in the way that individual atoms bond together.