Sulfur or sulphur (see spelling differences) is a chemical element with symbol S and atomic number 16. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S₈. Elemental sulfur is a bright yellow crystalline solid at room temperature. Chemically, sulfur combines with all elements except for gold, platinum, iridium, nitrogen, tellurium, iodine and the noble gases.