Reactive elements, halogens

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

Because of their reactivity, the halogens do not occur in the free elemental state but they are both widespread and abundant in the form of their ions, X. Iodine also occurs as iodate (see below). In addition to large halide mineral deposits, particularly of NaCl and KCl, there are vast quantities of chloride and bromide in ocean waters and brines. 

The halogens include fluorine, chlorine, bromine and iodine and all have been used in CVD reactions. They are reactive elements and exist as diatomic molecules, i.e., F2, CI2, etc. Their relevant properties are listed in Table 3.2. 

Fluorine does not occur in a free state in nature, and because fluorine is one of the most reactive elements, no chemical can free it from any of its many compounds. The reason for this is that fluorine atoms are the smallest of the halogens, meaning the electron donated by a metal (or some nonmetals) are closer to fluorines nucleus and thus exert a great force between the fluorine nuclei and the elements giving up one electron. The positive nuclei of fluorine have a strong tendency to gain electrons to complete the outer shell, which makes it a strong oxidizer. 

Unlike the metallic elements, halogens become less reactive going down the periodic table because of their generally decreasing electron affinity. Thus, their reactivity order is F2 > CI2 > Br2 > I2. Fluorine often reacts violently, chlorine and bromine somewhat less so, and iodine often sluggishly. 

Halogen azides are compounds with the general formula XN3, where X is one of the halogens. These compounds are extremely reactive and can be spontaneously explosive. Their reactions with water can produce toxic fumes of the elemental halogen, acid (e.g., HC1), and NOx. The compound vapors are irritants. 

On the basis of energy, explain why fluorine is an even more reactive element than might be expected when compared to the reactivity of the other halogens. 

Covalent hahdes can be prepared by various synthetic routes. The simplest are direct reactions of elemental halogens (equation 9), or hydrogen halides with elements (equation 10) or oxides (equation 11). In other processes, the oxides are reacted with a halogen halide in the presence of carbon to combine with the oxygen (equation 12) or other reactive carbon-halides (equation 13). Exchange of halogens can also take place (equations 14 16). Anhydrous halides can also be obtained by dehydration of metal halide hydrates, using reactants such as thionyl halide, which react with the hydrated water (equation 17). 

Because of their high reactivities, the halogens are not found as free elements in nature. Instead, they are found as halide ions (X ) in various minerals and in seawater (see Table 19.7). 

Alkali Metals and Halogens Are the Most Reactive Elements... 

The C = S bond is reactive toward a range of element-halogen bonds ... 

The elemental halogens exist as diatomic molecules that are both highly reactive and toxic. Many household products contain chlorine com-poimds that can generate chlorine gas if not handled properly. 

The halogens are toxic and reactive elements that are found only in compounds with other elements. Eluorine and chlorine are strong oxidizing agents and are prepared by electrolysis. 

Addition of a purge line, which is particularly important when reactive gases, e. g., metal halides, acids, and elemental halogens, are used. 

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