Oxygen Compounds of the Halogens

The oxygen compounds of the halogens (other than fluorine) are very important substances. A few of them, such as potassium chlorate, have been mentioned in earlier chapters. The chemistry of these substances is complex, but it can be systematized and clarified by correlation with the electronic theory of valence. This is the reason that the treatment of these compounds was not included in Chapter 9 but was postponed to this place. Some aspects of the chemistry of the halogens themselves and of the hydrogen halides are also presented in this chapter. 

Aldehydes, formates, primary, and secondary alcohols, amines, ethers, alkyl halides, compounds of the type Z—CH2—Z, and a few other compounds add to double bonds in the presence of free-radical initiators/ This is formally the addition of RH to a double bond, but the R is not just any carbon but one connected to an oxygen or a nitrogen, a halogen, or to two Z groups (defined as on p. 548). The addition of aldehydes is illustrated above. Formates and formamides " add similarly ... 

All the remaining halogens have unfilled d orbitals available and the covalency of the element can be expanded. Compounds and complex ions are formed both with other halogens and with oxygen in which the halogen can achieve a formal oxidation state as high as + 7. for example chlorine has formal oxidation states of +1 in the chlorate(I) anion CIO + 5 in the chlorate(V) anion CIO 3, and + 7 in the chlorate(VII) anion CIO4. ... 

Holmium has an oxidation state of +3 that, on a limited basis, can form a few compounds with the halogens and oxygen. They are of no commercial uses, and most holmium is used for research purposes. 

Another important group contains the spinels, named after the mineral MgAl204 see Table XXX(b)). The compounds of the fourth and fifth columns in Table XXX(b) are generally written with the formula Fe304, Co3S4, etc. All these examples show quite clearly that there is no essential distinction to be made between oxygen and sulphur salts, on the one hand, and halogen complexes, on the other. 

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