The Group 17 Elements F, Cl, Br, I, At

The high reactivity of fluorine results from a combination of the low F—F bond energy and the high strength of bonds from fluorine to other atoms. The small size and high electronegativity of the F atom account for many of the other differences between fluorine and the other halogens. 

The coordination number of the halogens in the -1 state is normally only 1, but exceptions are found in HXH+ cations, in polyhalide ions such as FC1F and I3, and when X ions occur as bridging ligands where the coordination number is 2. There are also triply bridging X ions in some metal atom cluster compounds. 

For fluorine there is little evidence for positive behavior even in the formal sense. In oxygen fluorides the F atom is probably somewhat negative with respect to oxygen whereas in C1F evidence from chlorine nuclear quadrupole coupling shows that the actual charge distribution involves partial positive charge on Cl. 

Bond polarities in other halogen compounds indicate the importance of forms such as I+CT in IC1 or I+CN in ICN. In general, when a halogen atom forms a bond to another atom or group more electronegative than itself, the bond will be 

Stable isotopes 19p 35C1,37C1 79Br, 81Br 127J None 

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The halogens are the family of nonmetal elements in group 17 (VIIA) that are located just to the right of the oxygen group 16 on the periodic table of chemical elements. They are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). 

Our last chance to view very active elements occurs in Group 7A(17). The halogens begin with fl uorine (F), the strongest electron grabber of all. Chlorine (Cl), bromine (Br), and iodine (I) also form compounds with most elements, and even rare astatine (At) is thought to be reactive [Group 7A(17) Family Portrait, p. 448]. 

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