The Halogen Elements

Abstract

Group 17 of the periodic table of the elements (see Table 1.1) consists of the so called halogen elements fluorine, chlorine, bromine, iodine, astatine and the recently discovered element 117 (Organessian et al. in Phys Rev Lett 104:142502, 2010), although it is not yet known if this element behaves similar to the other group 17 elements due to possible relativistic effects (see e.g. Pyykkö 2011b). Group 17 elements are characterised by an outer electron shell which contains seven electrons, so that only one electron needs to be added to give it a full noble gas configuration. This property makes that the dominant oxidation state, especially for the lighter elements of this group, is the -I oxidation state and they predominantly form ionogenic compounds. In the earth’s surface reservoir chlorine and bromine are most commonly found in aqueous solution in the oceans, as most of their salts are readily soluble in water, and in evaporite deposits while fluorine is most common in some fluoride rich minerals such as fluorite (CaF2), fluorapatite (Ca5(PO4)3F), and cryolite (Na3AlF6) as the alkaline earth fluorides (e.g. CaF2, MgF2) have a low solubility and precipitate out of waters with significant alkaline earth concentrations. Iodine has a relatively low concentration in seawater as it is efficiently removed from it by certain brown algae which are able to heavily concentrate iodine.