Allotropy

Name:
Allotropy
Detailed information:
(polymorphism). The existence of a substance in two or more forms which are significantly different in physical or chemical properties. The difference between the forms involves either (1) crystalline structure; (2) the number of atoms in the molecule of a gas; or (3) the molecular structure of a liquid. Carbon is a common example of (1), occurring in several crystal forms (diamond, carbon black, graphite) as well as several amorphous forms. Diatomic oxygen and triatomic ozone are instances of (2); and liquid sulfur and helium of (3). Uranium has three crystalline forms, manganese four, and plutonium no less than six. A number of other metals also have several allotropic forms which are often designated by Greek letters, e.g., α-, γ-, and Δ-iron.