allotropen

Allotropy is the property of an element to exist in two or more distinct structural forms in the same phase. The different forms, known as allotropes, arise from variations in how the atoms are arranged and bonded, which can produce markedly different physical and chemical properties.

Carbon provides some of the best-known allotropes. Diamond features a three-dimensional, sp3-bonded lattice that makes it extremely hard and an electrical insulator. Graphite consists of layered planes of sp2-bonded carbon that are slippery and a good conductor of electricity. Other forms, such as graphene and fullerenes (including C60), expand the range of carbon’s physical properties and applications.

Oxygen also exhibits allotropy. O2 (dioxygen) is the stable form at room temperature and is essential for most respiration, while O3 (ozone) is a less stable, highly reactive form that absorbs ultraviolet radiation in the atmosphere and can be toxic at ground level.

Other common examples include phosphorus, which exists as white, red, and black allotropes, each with different structures and reactivities; and sulfur, which primarily exists as the S8 ring at ambient conditions but also forms several polymeric and other allotropes under varying temperatures and pressures. Allotropy can reflect differences in energy, stability, color, conductivity, and reactivity, influencing material science, chemistry, and industrial applications.

Allotropy is distinct from chemical isomerism, which involves different arrangements of atoms within compounds. It highlights how elements can exhibit fundamentally different forms without changing their elemental identity.