Allotrope
Allotrope, two or more distinct physical forms of a chemical element in the same physical state. The term allotropy comes from the Greek allos tropos meaning “another shape.” Allotropes arise because of differing arrangements of an element’s atoms within its molecules or crystals. One of the best-known examples of allotropy is carbon , which has multiple distinct allotropes including graphite , diamond , and buckminsterfullerene . Carbon atoms in diamond form a rigid, three-dimensional structure, with each carbon atom bonded to four other carbon atoms. In graphite the carbon atoms form stacks of flat honeycomb layers with only weak intermolecular forces between layers, while buckminsterfullerene forms balls and tubes with structures reminiscent of the geodesic domes designed by the architect Richard Buckminster Fuller. Elements exhibiting allotropy include arsenic , antimony , iron , oxygen , phosphorus , selenium , sulfur , and tin . There are two main kinds of allotropy, monotropy