Allotropy is the phenomenon by which a chemical element can exist in two or more different physical forms, or allotropes, in the same physical state. These different structural forms have distinct properties, including physical state, density, and chemical reactivity, despite being composed of the exact same elements. The allotropic structure is determined by the arrangement of atoms and the types of chemical bonds linking them. Graphitic carbon is a prime example, exhibiting distinct forms such as diamond, graphite, and fullerene structures, each possessing unique hardness and electrical conductivity due to the varying geometric arrangements of the carbon atoms.