one of at least two different forms of an element. Different allotropes of a substance often have very different properties from each other; e.g. white phosphorus (P4) is a highly reactive and toxic substance that glows in air due to its high reactivity and possesses a molecular structure, while red phosphorus (the stuff used to make strikers on match boxes) is a non-toxic substance that has a polymeric structure.
White tin is a shiny, electrically conductive metal usefull for plating cans to prevent corrosion, while gray tin is a semiconductor that possesses no uses whatsoever
by eszett August 26, 2003

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