The existence of a chemical element in two or more forms, which may differ in the arrangement of atoms in crystalline solids, is termed as allotropy.
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The existence of an element in more than one crystalline forms is known as allotropy.
These forms of the element are called allotropes or allotropic forms. This happens when the atoms of the element are bonded together in a different way. Different bonding arrangements between atoms result in different structures with different chemical and physical properties. Only some elements like sulphur, phosphorus, carbon and tin are elements which show allotropy.
For example; Allotropic forms of Carbon;
In Graphite each carbon atom is covalently bonded to three other carbon atoms, leaving one electron spare. This results in atoms arranged in flat layers of hexagons, between which is a cloud of free delocalized electrons that is made up from the spare electrons.
Diamond has a tetrahedral structure. Each carbon atom is connected to four other carbon atoms by a covalent bond to form a giant crystal lattice.
Fullerenes, where the carbon atoms are bonded together in spheres, cylinders or egg-shaped formations. It is also known as Bucky minister Ball.
Graphene is the thinnest, lightest, strongest, most stretchy material ever created. A single layer extracted from graphite. In its hexagonal lattice, each carbon is bonded with three others, leaving a spare electron.
