Learning Outcomes

Describe the preparation, properties, and also uses of halogensDescribe the properties, preparation, and also uses that halogen compounds

The aspects in team 17 space the halogens. These room the aspects fluorine, chlorine, bromine, iodine, and astatine. These aspects are also reactive to occur easily in nature, yet their compounds are widely distributed. Chlorides room the many abundant; although fluorides, bromides, and also iodides are less common, castle are fairly available. In this section, us will examine the occurrence, preparation, and properties that halogens. Next, we will examine halogen compounds with the representative metals complied with by an examination of the interhalogens. This ar will conclude v some applications that halogens.

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Occurrence and Preparation

All the the halogens happen in seawater together halide ions. The concentration that the chloride ion is 0.54 M; that of the other halides is much less than 10–4M. Fluoride likewise occurs in minerals such as CaF2, Ca(PO4)3F, and also Na3AlF6. Chloride also occurs in the good Salt Lake and also the Dead Sea, and in considerable salt beds the contain NaCl, KCl, or MgCl2. Component of the chlorine in her body is present as hydrochloric acid, i beg your pardon is a component of stomach acid. Bromine compounds occur in the Dead Sea and underground brines. Iodine link are uncovered in small quantities in Chile saltpeter, underground brines, and sea kelp. Iodine is important to the role of the thyroid gland.

The ideal sources the halogens (except iodine) room halide salts. The is possible to oxidation the halide ions to free diatomic halogen molecules by assorted methods, depending upon the ease of oxidation that the halide ion. Fluoride is the most an overwhelming to oxidize, whereas iodide is the easiest.

The major method because that preparing fluorine is electrolytic oxidation. The most common electrolysis procedure is to use a molten mixture the potassium hydrogen fluoride, KHF2, and anhydrous hydrogen fluoride. Electrolysis causes HF to decompose, developing fluorine gas in ~ the anode and also hydrogen in ~ the cathode. The is vital to save the 2 gases be separated to stop their explosive recombination to revolutionary hydrogen fluoride.

Most advertisement chlorine originates from the electrolysis of the chloride ion in aqueous remedies of salt chloride; this is the chlor-alkali process discussed previously. Chlorine is likewise a product of the electrolytic manufacturing of steels such together sodium, calcium, and magnesium from their fused chlorides. It is also feasible to prepare chlorine by the chemical oxidation that the chloride ion in acid solution with strong oxidizing agents such together manganese dioxide (MnO2) or salt dichromate (Na2Cr2O7). The reaction through manganese dioxide is:

extMnO_2left(s ight)+2 extCl^-left(aq ight)+4 extH_3 extO^+left(aq ight)longrightarrow extMn^2+left(aq ight)+ extCl_2left(g ight)+6 extH_2 extOleft(l ight)

The commercial preparation of bromine involves the oxidation the bromide ion by chlorine:

2 extBr^-left(aq ight)+ extCl_2left(g ight)longrightarrow extBr_2left(l ight)+2 extCl^-left(aq ight)

Chlorine is a stronger oxidizing agent 보다 bromine. This technique is important for the manufacturing of basically all residential bromine.

Some iodine comes from the oxidation the iodine chloride, ICl, or iodic acid, HlO3. The commercial ready of iodine uses the palliation of sodium iodate, NaIO3, one impurity in shop of Chile saltpeter, v sodium hydrogen sulfite:

2 extIO_3^-left(aq ight)+5 extHSO_3^-left(aq ight)longrightarrow 3 extHSO_4^-left(aq ight)+2 extSO_4^2-left(aq ight)+ extH_2 extOleft(l ight)+ extI_2left(s ight)

Properties that the Halogens


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Figure 1. Chlorine is a pale yellow-green gas (left), gaseous bromine is deep orange (center), and also gaseous iodine is violet (right). (Fluorine is so reactive the it is as well dangerous come handle.) (credit: Sahar Atwa)


Fluorine is a pale yellow gas, chlorine is a greenish-yellow gas, bromine is a deep reddish-brown liquid, and also iodine is a grayish-black crystalline solid. Liquid bromine has actually a high vapor pressure, and also the red vapor is conveniently visible in Figure 1. Iodine crystals have a remarkable vapor pressure. As soon as gently heated, this crystals sublime and kind a beautiful deep violet vapor.

Bromine is only slightly dissolve in water, yet it is miscible in all proportions in less polar (or nonpolar) solvents such as chloroform, carbon tetrachloride, and carbon disulfide, creating solutions that vary from yellow come reddish-brown, depending upon the concentration.

Iodine is soluble in chloroform, carbon tetrachloride, carbon disulfide, and many hydrocarbons, offering violet services of I2 molecules. Iodine dissolves just slightly in water, giving brown solutions. That is rather soluble in aqueous solutions of iodides, v which it develops brown solutions. This brown solutions an outcome because iodine molecules have empty valence d orbitals and also can act together weak Lewis acids towards the iodide ion. The equation for the reversible reaction the iodine (Lewis acid) with the iodide ion (Lewis base) to kind triiodide ion, extI_3^-, is:

extI_2left(s ight)+ extI^-left(aq ight)longrightarrow extI_3^-left(aq ight)

The easier it is to oxidize the halide ion, the more daunting it is for the halogen come act together an oxidizing agent. Fluorine usually oxidizes an facet to its highest oxidation state, conversely, the more heavier halogens may not. Because that example, once excess fluorine reacts v sulfur, SF6 forms. Chlorine provides SCl2 and bromine, S2Br2. Iodine does no react through sulfur.

Fluorine is the most powerful oxidizing agent of the recognized elements. It spontaneously oxidizes many other elements; therefore, the turning back reaction, the oxidation that fluorides, is very daunting to accomplish. Fluorine reacts directly and also forms binary fluorides with all of the facets except the lighter noble gases (He, Ne, and also Ar). Fluorine is such a solid oxidizing certified dealer that plenty of substances ignite on contact with it. Fall of water inflame in fluorine and kind O2, OF2, H2O2, O3, and HF. Wood and asbestos ignite and also burn in fluorine gas. Most warm metals burn strongly in fluorine. However, the is feasible to take care of fluorine in copper, iron, or nickel containers, because an adherent film of the fluoride salt passivates your surfaces. Fluorine is the only aspect that reacts directly with the noble gas xenon.

Although the is a strong oxidizing agent, chlorine is less energetic than fluorine. Mixing chlorine and also hydrogen in the dark provides the reaction in between them to it is in imperceptibly slow. Exposure of the mixture come light reasons the two to reaction explosively. Chlorine is also less active towards metals than fluorine, and also oxidation reactions typically require higher temperatures. Molten salt ignites in chlorine. Chlorine strikes most nonmetals (C, N2, and also O2 are significant exceptions), forming covalent molecular compounds. Chlorine generally reacts v compounds that contain just carbon and also hydrogen (hydrocarbons) by including to multiple bond or by substitution.

In cold water, chlorine experience a disproportionation reaction:

extCl_2left(aq ight)+2 extH_2 extOleft(l ight)longrightarrow extHOClleft(aq ight)+ extH_3 extO^+left(aq ight)+ extCl^-left(aq ight)

Half the chlorine atoms oxidize come the 1+ oxidation state (hypochlorous acid), and the other fifty percent reduce come the 1- oxidation state (chloride ion). This disproportionation is incomplete, so chlorine water is one equilibrium mixture the chlorine molecules, hypochlorous acid molecules, hydronium ions, and also chloride ions. As soon as exposed to light, this solution undergoes a optical chemicals decomposition:

ext2HOClleft(aq ight)+2 extH_2 extOleft(l ight),,,xrightarrow extsunlight,,,2 extH_3 extO^+left(aq ight)+2 extCl^-left(aq ight)+ extO_2left(g ight)

The nonmetal chlorine is an ext electronegative than any kind of other facet except fluorine, oxygen, and also nitrogen. In general, very electronegative facets are an excellent oxidizing agents; therefore, we would mean elemental chlorine to oxidize all of the other elements except because that these 3 (and the nonreactive noble gases). Its oxidizing property, in fact, is responsible for its major use. For example, phosphorus(V) chloride, an important intermediate in the preparation of insecticides and chemical weapons, is made by oxidizing the phosphorus through chlorine:

extP_4left(s ight)+10 extCl_2left(g ight)longrightarrow 4 extPCl_5left(l ight)

A great deal the chlorine is likewise used to oxidize, and also thus to destroy, essential or organic materials in water purification and in bleaching.

The chemistry properties of bromine are comparable to those that chlorine, although bromine is the weaker oxidizing agent and its reactivity is less than the of chlorine.

Iodine is the least reactive that the halogens. The is the weakest oxidizing agent, and the iodide ion is the most conveniently oxidized halide ion. Iodine reacts v metals, however heating is frequently required. The does no oxidize various other halide ions.

Compared v the other halogens, iodine reacts only slightly through water. Traces of iodine in water react v a mixture that starch and iodide ion, forming a deep blue color. This reaction is a very sensitive test for the visibility of iodine in water.

Halides that the Representative Metals

Thousands of salts of the representative metals have actually been prepared. The binary halides are vital subclass the salts. A salt is one ionic compound written of cations and also anions, various other than hydroxide or oxide ions. In general, it is possible to prepare this salts native the metals or from oxides, hydroxides, or carbonates. Us will illustrate the general varieties of reactions for preparing salts with reactions supplied to prepare binary halides.

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The binary compound of a metal with the halogens are the halides. Many binary halides room ionic. However, mercury, the elements of team 13 v oxidation claims of 3+, tin(IV), and also lead(IV) kind covalent binary halides.

The direct reaction of a metal and also a halogen create the halide the the metal. Examples of this oxidation-reduction reaction include:

extCdleft(s ight)+ extCl_2left(g ight)longrightarrow extCdCl_2left(s ight) ext2Galeft(l ight)+3 extBr_2left(l ight)longrightarrow 2 extGaBr_3left(s ight)