allotrope

Allotropy refers to a chemical element existing in two or more distinct forms. These forms can differ in how their atoms are arranged in solid crystals or in the number of atoms within their molecules. This phenomenon is similar to polymorphism in compounds.1

Elements like tin, carbon, sulfur, phosphorus, and oxygen exhibit allotropy. For instance, carbon has common allotropes such as diamond and graphite, which have different atomic structures and properties. Oxygen exists as diatomic O₂ and triatomic ozone (O₃).123

Allotropes can be monotropic, meaning one form is always the most stable, or enantiotropic, where different forms are stable under varying temperatures and pressures, allowing for reversible transitions between them.1