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36. SUBGROUP OF HALOGENS.
The subgroup of halogens includes elementy:ftor, chlorine, bromine, iod, astatine. All elements of this subgroup - pronounced nonmetals. In free state halogens form the substances consisting of the diatomic molecules F2, Cl2, Br2, I2.
STAY IN THE NATURE Content in crust: fluorine - 0,028%, chlorine - 0,19%, bromine - 0,0006%, iod - 0,000006%, astatine - traces
Properties of the VII-A elements of subgroup.
Element Fluorine
FChlorine
ClBromine
BrIod
IProperty Order number of element 9 17 35 53 Relative atomic mass 18,998 35,453 79,904 126,904 Melting temperature, 0C - 209,16 - 102 - 7,3 113,5 Boiling temperature, 0C - 187,5 - 34,1 58,8 185,2 G/cm3 density 1,11
1,57 3,14
4,94for liquid phase at t. kip at 20 0C and standard atmosphere pressure Coloring in gaseous state yellowish
greenyellow
greenred
brownviolet Oxidation levels - 1 - 1,+1, +3, +5, +7 - 1,+1, +3, +5 - 1,+1, +3, +5, +7
Receiving halogens.
fluorine chlorine bromine iod 1. KF electrolysis
2KF 2K+ F2
2. Heating of rekotory fluorides
2CoF31. Electrolysis of chlorides
2KCl
2. Dickon's method
4HCl + O2 2H2O
3. Chlorohydrogen oxidation
2KMnO4 + 16HCl =2KCl + 2MnCl2 + 8H2O + 5Cl21. Replacement from bromides
MgBr2 + Cl2MgCl21. Iodate processing by sodium hydrosulphite
2NaIO3 + 5NaHSO32Na2SO4Chemical properties of halogens.
Let's consider properties of halogens on the example of chlorine:
1. Interaction with metals Mg + Cl2MgCl2 2. Reactions with nonmetals H2 + Cl22HCl 3. Interaction with alkalis in the cold 2NaOH + Cl2NaCl 4. Interaction with alkalis when heating 6NaOH + 5. Replacement of less active halogens from halogenides 2KBr + Cl22KCl 6. With water H2O + Cl2HCl + HClO (chlorine water)
Use of halogens.
Fluorine widely apply as the fluorinating agent when receiving different fluorides (SF6, BF3, WF6 and others) including compounds of inert gases of xenon (Xe) and krypton (Kr). UF6 uranium hexafluoride is applied to isotope separation of uranium (U). Fluorine is used in production of teflon, other ftoroplast, fluoroelastomers, fluorinated organic substances and materials which widely apply in the equipment, especially when resistance to aggressive environments, high temperature, etc. is required. Chlorine apply in production of chlorine-containing organic compounds (60-75%), non-organic substances (10-20%), to whitening of cellulose and fabrics (5-15%), to sanitary needs and disinfecting (chlorination) of water. Bromine bromine is applied when receiving number of non-organic and organic substances, in analytical chemistry. Compounds of bromine use as fuel additives, pesticides, burning inhibitors, and also in the photo. The medicines containing bromine are widely known. It should be noted that ordinary expression: "the doctor has registered bromine on tablespoon after food" means, certainly, only that aqueous solution of sodium bromide (or potassium), but not pure bromine is registered. The calming effect of bromic medicines is based on their ability to strengthen processes of braking in the central nervous system. Iod iod is applied to receiving high-pure titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb) and other metals (so-called iodidny refinement of metals). At iodidny refinement initial metal with impurity is transferred to form of flying iodides, and then the received iodides decompose on the heated fine end. Thread is made of in advance purified metal which is subjected to refinement. Its temperature is selected such that on thread there could be decomposition only of iodide of the purified metal, and other iodides remained in vapor phase.
Use iod and in the iodic glow lamps having tungsten spiral and which are characterized by big endurance. As a rule, in such lamps of couple of iod are in the environment of heavy inert gas of xenon (Xe) (lamps often call xenon) and react with the atoms of tungsten (W) evaporating from heated spiral. Flying iodide in these conditions which appears near spiral again sooner or later is formed. There is immediate decomposition of iodide, and the released tungsten (W) appears on spiral again. Iod is applied also in nutritional supplements, dyes, catalysts, in the photo, in analytical chemistry.
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