Halogens

These elements take place in nature in halide minerals. CaF₂ is extremely insoluble in water, but another halide ion is simply washed out of rocks and are abundant in sea water. Volcanic emissions consist of small amounts of HF and HCl but these gases are extremely soluble and washed out of the atmosphere rapidly. Marine organisms generate small quantities of methyl compounds like CH₃Cl that are oxidized and washed out also. A number of synthetic organohalogen compounds pose environmental troubles since natural chemical processes split them down extremely in slow speed. Organochlorine compounds of concern involve dioxins and persistent insecticides like DDT, and volatile chlorofluorocarbons (CFCs) used like aerosol propellants and in refrigerators. CFCs oppose photochemical fails in the lower atmosphere and can enter the stratosphere in which short-wavelength UV radiation divide them to generate Cl atoms, that then act like catalysts for the decomposition of UV-absorbing ozone.