allotropy əlŏ´trəpē [key] [Gr.,=other form]. A chemical element is said to exhibit allotropy when it occurs in two or more forms in the same physical state; the forms are called allotropes. Allotropes generally differ in physical properties such as color and hardness; they may also differ in molecular structure or chemical activity, but are usually alike in most chemical properties. Diamond and graphite are two allotropes of the element carbon . Ozone is a chemically active triatomic allotrope of the element oxygen . Phosphorus , sulfur , and tin also exhibit allotropy. Many metals have allotropic crystalline forms that are stable at different temperatures. Polymorphism is an analogous phenomenon observed in chemical compounds.
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