Allotropy: Difference between revisions

Latest revision as of 11:56, 10 March 2008

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+#REDIRECT [[Allotrope]]
-In [[chemistry]], '''allotropy''' (adjective '''allotropic''') means the existence, especially in the solid state, of two or more crystalline or molecular structural forms of an [[element]]. An element can exist in several forms or modifications that not only have strongly different outer appearances, but also have different physical properties. Yet, chemically it is one and the same element. The classic  example is formed by the three allotropes [[diamond]], [[graphite]] and [[charcoal]], which consist of pure [[carbon]] and burn in the presence of [[oxygen]], giving [[carbon dioxide]]. Diamond is extremely hard and often transparent, graphite is soft, flaky, and black,  and charcoal is brittle and black.
-Another example is [[rhombic]] and [[monoclinic]] [[sulphur]], which are two different [[crystal structure]]s of the element sulphur.
-Allotropy must be distinguished from the existence of different phases of the same substance, liquid, solid, or gas.
-Allotropy was discovered in 1821 for sulphur by the German chemist [[Eilhard Mitscherlich]].
-==External link==
-[http://www.arb.ca.gov/toxics/tac/appendxc.htm Glossary California Air Resources Board]