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. Chlorine is by far the most abundant of the halogens, and the only one needed in relatively large amounts (as chloride ions) by humans. Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms these are known as halogenated compounds or organic halides. Group 17 is the only group containing elements in all three phases at room temperature. Their electronegativity and electron affinities decrease going down the group, and their sizes, melting and boiling points increase.įluorine and chlorine are diatomic gases at room temperature, bromine is a liquid, and iodine and astatine are solids. The halogens demonstrate several periodic trends very well. They can also react with each other to form the so-called interhalogens. SF 6) and were instrumental in the formation of the first compounds of the noble gases (eg. The halogens are found in some hypervalent compounds (eg. Care should be taken when handling these acids, particularly at high concentrations. Hydrohalic acids, diatomic compounds of one hydrogen atom and one halogen atom, are particularly strong acids owing to high halogen electron affinity. This is particularly true for fluoride ions, which can easily diffuse through the skin and enter the bloodstream. Halogen anions in the body can bind to potassium, calcium and magnesium cations, rendering them useless. They also do not exist as isolated atoms in their elemental forms instead, they each share one electron with one other atom to form diatomic molecules.Ī third consequence of the halogens' nearly filled valence shell is high reactivity towards cationic or low-ionization-potential species. ![]() As such, the halogens have a strong tendency to form ions with a charge of -1 in order to complete their valence shells. The valence shells of halogen atoms need only one more electron to form a completely filled shell of either eight or eighteen electrons.
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