Chemistry » Metals, Metalloids, and Nonmetals » Occurrence, Preparation, and Properties of Halogens



Compounds formed from two or more different halogens are interhalogens. Interhalogen molecules consist of one atom of the heavier halogen bonded by single bonds to an odd number of atoms of the lighter halogen. The structures of IF3, IF5, and IF7 are illustrated in the figure below. Formulas for other interhalogens, each of which comes from the reaction of the respective halogens, are in the table below.

Three ball-and-stick models are shown. The left structure, labeled, “I F subscript 3,” shows a purple atom labeled, “I,” bonded to three green atoms labeled, “F,” and with two lone pairs of electrons. The middle structure, labeled, “I F subscript 5,” shows a purple atom labeled, “I,” bonded to five green atoms labeled, “F,” and with one lone pair of electrons. The right image, labeled, “I F subscript 7,” shows a purple atom labeled, “I,” bonded to seven green atoms labeled, “F.”

The structure of IF3 is T-shaped (left), IF5 is square pyramidal (center), and IF7 is pentagonal bipyramidal (right).

Note from the table below that fluorine is able to oxidize iodine to its maximum oxidation state, 7+, whereas bromine and chlorine, which are more difficult to oxidize, achieve only the 5+-oxidation state. A 7+-oxidation state is the limit for the halogens.

Because smaller halogens are grouped about a larger one, the maximum number of smaller atoms possible increases as the radius of the larger atom increases. Many of these compounds are unstable, and most are extremely reactive. The interhalogens react like their component halides; halogen fluorides, for example, are stronger oxidizing agents than are halogen chlorides.

The ionic polyhalides of the alkali metals, such as KI3, KICl2, KICl4, CsIBr2, and CsBrCl2, which contain an anion composed of at least three halogen atoms, are closely related to the interhalogens. As seen previously, the formation of the polyhalide anion \({\text{I}}_{3}{}^{-}\) is responsible for the solubility of iodine in aqueous solutions containing an iodide ion.


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