The Fluorine Group
The Fluorine Group
The Fluorine Group of the Periodic Table, whose elements are known as halogens (Greek halos and genes, meaning salt-forming), consists of fluorine F, chlorine Cl, bromine Br, iodine I, and astatine At. The outer electron structure ns2np5 characterizes all five of the elements, with n representing principal quantum numbers 2, 3, 4, 5, and 6, respectively. The ns2np5 indicates that oxidation number possibilities are −I, I, III, V, and VII with F showing only −I (except for the unstable HOF). The bonding in the oxidation state of −I is sometimes ionic and sometimes covalent, while that in the other states is covalent. Fluorine is the most electronegative element in the Periodic Table, and as one descends the group, the electronegativities decrease. Fluorine stands out as considerably different from the other elements, there being numerous discontinuities in properties between it and Cl. Astatine also differs from the other elements in that all its isotopes are radioactive, the longlived At-210 having a half life of 8.1 days. Covalent radii in pm are as follows: F(71), Cl(99), Br(114), I(133), and At (147). Ionic radii in pm are as: F−(119), Cl−(167), Br−(182), and I−(206). a. E–pH diagram. Figure 11.1 depicts the E–pH diagram for F with the soluble species (except H+) at 10−1.0 M. The diagram is valid only in the absence of substances with which F forms soluble complexes or insoluble compounds. The species which have been considered are F2, OF2, F−, HF, and HF2−. This last species is not very stable and will appear on the diagram only at higher F− concentrations. It shows up in between HF and F−. The E–pH diagram emphasizes the very strong oxidizing power of F2 and indicates that it will easily attack HOH to produce OF2. The species oxygen fluoride OF2 is also unstable but persists in solution longer than F2.
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