Fluorine is a chemically-active element, Atomic #9 on the Periodic Table. Because of its properties, it is classified with the Halogens on the Table, along with Chlorine, Bromine, Iodine, and Astatine. Oxygen, while right next to Fluorine at #8, is classified as an Other Non-Metal, meaning that while it does not share properties with the Noble Gasses and Metalloids, it also does not contain properties of the Halogens. This means that while Fluorine is atomically further away from Chlorine than it is from Oxygen, Fluorine shares more chemical properties with Chlorine. One interesting property of Fluorine is that it creates compounds with the Inert Gasses, which normally do not react with other chemical elements (thus being called "inert"). While both Oxygen and Chlorine are chemically-active, they cannot form compounds with the inert gasses, while Fluorine is the most chemically-active of all the elements.