Allotropes of sulphur. • Sulphur, S, atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula S₈. Elemental sulfur is a bright yellow, crystalline solid at room temperature. • Sulphur forms several polyatomic molecules, the best known allotrope is the one first mentioned. (Allotropes are the different forms in which an element can exist, for example, allotropes of carbon are diamonds, graphite and