Fluorine is a poisonous and corrosive gas and breathing just a tiny bit of fluorine can damage the lungs. But, fluorine's reactivity makes it a very useful element - it is used in toothpaste and in nonstick surfaces for frying pans, and to refine uranium fuel that is utilized in nuclear power plants. Students learn about fluorine's phase at room temperature, its place within a very special group, VIIA, called the halogens, on the periodic table, its physical and chemical properties, and about its isotopes and atomic weight.