HALOCABON

Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms: fluorine, chlorine, bromine or iodine. Chlorine halocarbons are the most common and are called organochlorides. There are also compounds such as methylammonium chloride that include carbon atoms and noncovalent halogen atoms, also called inorganic halogens. Unlike halocarbon halogens, noncovalent halogen atoms will usually dissociate and ionize in water. Halocarbons are a class of organic compounds containing covalently bonded fluorine, chlorine, bromine, or iodine.
Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms; they are known as halogenated compounds. Chlorine is by far the most abundant of the halogens, and the only one needed in relatively large amounts (as chloride ions) by humans. For example, chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA and are also used by the body to produce stomach acid. Iodine is needed in trace amounts for the production of thyroid hormones such as thyroxine. On the other hand, neither fluorine nor bromine are believed to be really essential for humans, although small amounts of fluoride does make teeth enamel somewhat more resistant to attack