The formula of calcium fluoride is CaF2. It is made up of calcium ions, Ca2+ and fluoride ions, F-.
Calcium fluoride, or fluorite, is an interesting mineral from which the term fluorescence was coined. Fluorescence is the phenomenon by which a substance emits light after absorbing electromagnetic radiation of a different wavelength. In the case of the sample of fluorite shown below, it emits blue light after absorbing certain wavelengths of ultraviolet radiation. Different samples of fluorite may emit different colours.
Fluorine is the most reactive element in group 7, chlorine the second element in the group is the next most reactive and so on. Thus, the reactivity of the halogens is said to decrease on going down the group.
What would you predict would happen if chlorine Cl2, were added to an aqueous solution of potassium iodide, KI?