Different forms of the same Substance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of in the same physical state. Allotropy in crystalline materials is called Situation in which a single chemical composition can exist with two or more different crystal structures. Transformations between crystal structures of the same chemical compound are called polymorphic transformations. These are of three types of polymorphism: displacive, reconstructive, and order-disorder. Examples of polymorphs include: • Silica (SiO2): α quartz, β. An oxygen molecule (O3) composed of three oxygen atoms. (O3) and dioxygen (O2) are allotropes of gaseous Element that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only.