Halogen Family

The p-Block Elements Halogen Family CHEMICAL CHARACTERISTICS : ELECTRONIC CONFIGURATION : The general outer electronic configuration of elements Halogens are most reactive due to : 2 5 of VII group is ns np . Hence these elements belong (i) Low bond dissociation energy. to p–block. (ii) High electron affinities Element Configuration In halogen F2 is the most reactive I2 is least reactive Fluorine [F9] [He] 2s22p5 Reaction with water : Chlorine [Cl17] [Ne] 3s23p5 H 2O F2   O2, O3 Bromine [Br35] [Ar] 3d104s24p5 H2O  HX, HXO (Cl2 or Br2) X2  sun light Iodine [I53] [Kr] 4d105s25p5 H 2O I2   no reaction Astatine [At ] [Xe] 4f14 5d10 6s26p5 85 Reaction with metals and nonmetals : * * First four member F, Cl, Br and I are called halogens * as their salts are present in sea water. * At is radioactive, artificially prepared and unstable. F2 combines with metals to give fluorides. Cl 2, combines with large number of metals. The reaction is slow. * Strong tendency to accept one electron to acquire stable inert gas configuration. Hence exhibit nonmetallic behaviour. * Br2 and F2 do not react with noble and less active metals. * High electronegativity makes them very reactive and * here they are not available in free state. Examples : CuF2, NaF, KI, NaCl, NaBr, MgCl2 * Except At, the members are found in combined state in suitable quantities in nature. * X2 combines with nonmetals like S, P, As etc. Reaction with hydrocarbons : F2 decomposes hydrocarbons GENERAL PHYSICAL PROPERTIES : CH4 + 2F2  C + 4HF (a) Physical state : Cl2  Cl2 and Br2 gives substitution reaction. CH4  hv CH3Cl, CH2Cl2, CHCl3, CCl4 F Cl Br I Gas Gas Fuming liquid Volatile solid (b) Colour : Halogens are coloured F Cl Br I Pale Greenish Reddish brown Deep violet yellow yellow The molecules absorb visible region of light for excitation of outer electrons to higher energy levels. Fluorine – [Absorbs violet light]  Appears pale yellow Iodine – [Absorbs yellow light]  Appears violet * I2 has practically no action on hydrocarbons. Halogen displacement reaction : * Fluorine replaces (Cl, Br, I) * Chlorine replaces (Br, I) 2NaX + F2  2NaF + X2 [X = Cl, Br, I] 2NaX + Cl2 2NaCl + X2 [X = Br, I] 2NaX + Br2  2NaBr + X2 [X = I] Reaction with alkalines : Cl2, Br2 and I2 behave similarly when treated with alkali (It is a disproportionation reaction) The p-Block Elements Stability of conjugate bases : Cold and dilute alkali : Sodium hypohalite ClO–, ClO2–, ClO3–, ClO4– are the conjugate bases of the acids HClO, HClO2, HClO3 and HClO4. Hot and concentrated alkali : Conjugate bases [HX + H2O 2X2 + 6NaOH  5NaX + NaXO + H2O The stability of conjugate bases of oxy acids increases with the increase in the number of oxygen atoms in the anion thus : ClO– < ClO2– < ClO3– < ClO4– X2 + 2NaOH  NaX + NaXO + H2O Sodium halate F2 behaves differently with alkalies : F2 + 2NaOH (dil)  2NaF + OF2 + H2O ANOMALOUS BEHAVIOUR OFFLUORINE: Anomalous behaviour of Fluorine is due to : 2F2 + 4NaOH  4NaF + O2 + 2H2O Reaction with hydrogen : dark H2 + F2  2HF * Small size, – high electronegativity * Non – availability of d–orbital, –low dissociation energy * Highest positive reduction potential. diffused sunlight   2HCl H2 + Cl2    2HBr H2 + Br2  H2 + I2 * * * Main points of differences are : 2HI (catalyst) OXY-ACIDS OF HALOGENS : H3O+ + A–] * Fluorine shows only –1 oxidation state. * Fluorine exhibits one as its covalency. F forms only one oxy acid HOF (hypfluorous acid) * Cl, Br and I form four series of acids. * Fluorine forms inter and intramolecular H–bonding. Acid–character : Fluorine forms two series of salts [NaHF2 and Na2F2] * The acid – character of the oxy acids of same halogen increases with the increase in the oxidation number * of the halogen. Example : HF is weak acid as compared to HCl, HBr and HI. AgF is soluble in water while AgCl, AgBr and AgI are insoluble. HOCl > HOBr > HOI * Fluorine form two series of salts [NaHF2 and Na2F2] HClO3 > HBrO3 > HIO3 * AgF is soluble in water while AgCl, AgBr and AgI are insoluble. * Fluorine does not forms oxy acids while oxy acids of other halogens are well known (HClO3, HBrO, HiO4 etc.] Example : HOCl > HClO2 > HClO3 > HClO4 * The order of oxidizing power of parhelic acid (or their salts) Fluorine is most reactive amongst halogens (due to low F–F energy). * Fluorine forms SF6 whereas no other halogens forms SX6. * CaF2 is insoluble in water whereas CaCl2, CaBr2 and CaI2 are soluble. HClO4 > HBrO4 > HIO4 Oxidising power : Oxidizing power of the oxy acids of same halogen decreases with the increase of O.S. of halogen. follows the order : ClO4 < BrO4– < IO4– Thermal stability : Thermal stability of oxyacid of * chlorine follows the order : HOCl < HClO2 < HClO3 < HClO4 Fluorides are more stable than other halides UF6 is more stable than UCl6. NF3 is stable while NCl3 is unstable and explosive. SF6 is stable SCl6 is unstable. The p-Block Elements Reacts with water to give O2 and O3 * Fluorine directly combines with carbon whereas Reacts with other halogens to form inter halogen other halogens do not. compounds [ClF, ClF3, IF3, IF7 etc.] * [F2 + H2O] gives oxone while other halogens do * Reacts with CH4 explosively to give CH3, F, CH2F2, not give oxone. CHF3 and CF4. * F– has more complex forming tendency as compared 3. Uses : to other halides ions. [(AlF6]3–, [FeF6]3–] (i) Fluorides are used as insecticides (CaF2 is added * Fluorine does not form poly halide ion like I3–, Br3– to tooth paste) etc. (ii) Sodium and antimony fluorides are used as mordants in dyeing industry. FLUORINE : (iii) Freons (poly chloro fluoro alkanes) are used in 1. Occurrence : refrigeration and air conditioning. Fluorine is very reactive and hence it does not occur (iv) Br2 and HF are used as catalyst in petroleum in free state. In combined state it occurs as : industry. (v) CuF2 is used in ceramic industry. * Fluorspar [CaF2] (vi) Teflon (C2F4) is polymer used as insulting material * Cryolite [Na3AlF6] in cables. * Fluorapatite [CaF2 . 3Ca3 (PO4)2] (vii) For the separation of U235 from natural uranium, Fluorine occurs in small quantities in plant, teeth, UF6 is used. bones, sea water etc. (viii) Na3 AlF6 and CaF2 are used for the extraction of aluminium. 2. Reaction of F2 are : Directly combines with metals and non metals (ix) Sodium fluoro acetate is used as rat poison. * * 2Na + F2  2NaF2 2B + 3F2  2BF3 Mg + F2  MgF2 C + 2F2  CF4 2Ag + F2  2AgF P4 + 10F2  4PF5 Reaction with H2, O2 : H2 + F2  H2F2 (expoldes even in dark) O2 + F2  O2F2 (explodes in presence of silent electric discharge) Reaction with HCl, H2S and NH3 : 2HCl + F2  2HF + Cl2 H2S + 4F2  2HF + SF6 2NH3 + 3F2  6HF + N2 Reaction with NaOH : 2F2 + 2NaOH (dil)  2NaF + OF2 + H2O 2F2 + NaOH (conc.)  4NaF + O2 + 2H2O Reaction with halides : 2NaX + F2  2NaF + X2 [X = Cl–, Br–, I–] [X2 = Cl2, Br2, I2] CHLORINE : 1. Occurrence : It is widely distributed in the form of chlorides. NaCl is the most important chloride occurs in sea water, lakes and in rocks. Chloride mineral are : * Rock salt [NaCl] . Sylvine (KCl) * Carnallite [KCl.MgCl2.6H2O] * Horn silver [AgCl] 2. Preparation : (1) By the oxidation of HCl by MnO2, K2Cr2O7, PbO2, KMnO4, CaOCl2, NaClO etc. MnO 2 + 4HCl  MnCl 2 + 2H 2 O + Cl 2 (Lab. method) NaClO + 2HCl  NaCl + H2O + Cl2 CaOCl2 + 2HCl  CaCl2 + H2O + Cl2 2KMnO4 + 16HCl  2KCl + 2MnCl2 + 8H2O + 5Cl2 K2Cr2O7 + 14HCl  2KCl + 3CrCl3 + 7H2O + 3Cl2 (2) Commercial methods : The p-Block Elements Oxidizing and bleaching action of Cl2 : (a) [Decon’s process] Air oxidation of hydrochloric acid in presence of copper (II) chloride catalyst. [Cl2 on reaction with water liberates nascent oxygen. Hence it is a powerful oxidant.] Cl2 + H2O  2HCl + [O] CuCl2  2H2O + 2Cl2 4HCl + O2  (Permanent) Coloured substance + [O]  Colourless substance other reactions : (b) By the electrolysis of aqueous NaCl solution : At anode Cl2 is liberated At cathode SO2 + 2H2O + Cl2  H2SO4 + 2HCl H2 is liberated Na2SO3 + H2O + Cl2  Na2SO4 + 2HCl (Caster – Kellner and Nelson cell) Na2SO3 + H2O + Cl2  Na2SO4 + 2HCl + S 3. Properties : Physical characteristics : * Cl2 is greenish yellow gas. 2KBr + Cl2  2KCl + Br2 * Cl2 is poisonous having a suffocating odour. 2KI + Cl2  2KCl + I2 * Cl2 is soluble in water and carbon disulphide. 4. * Cl2 is 2.5 times heavier than air. (i) Used in the manufacture of bleaching powder, hydrochloric acid, hypochlorites, chlorates, CHCl3, CCl4, DDT, Phosgene, mustard gas etc. Chemical characteristics : Reaction with metals and nonmetals. 2Na + Cl2  2NaCl 2P + 5Cl2  2PCl5 Ca + Cl2  CaCl2 2S + Cl2  S2Cl2 Liberation of Br2 and I2 from KBr and KI Uses of chlorine : (ii) Used in the purification of drinking water. (iii) Used in extraction of Au and Pt. Reaction with SO2, CO and NO (iv) Used as a bleaching agent for cotton fabrics, paper and rayon. SO2 + Cl2  SO2Cl2 (sulphuryl chloride) (v) Used as a germicide and disinfectant. CO + Cl2  COCl2 (vi) Used as an oxidant. 2NO + Cl2  2NOCl BROMINE Reaction with NH3 : 1. 8NH3 (excess) + 3Cl2  6NH4Cl + N2 Occurrence : Bromine occurs in the combined state as bromides of Na, K and Mg. It was discovered by Ballard (1826). If is present in : NH3 + 3Cl2 (excess)  NCl3 + 3HCl Reaction with NaOH and Ca(OH)2 : Cl2 + 2NaOH (cold dil.)  2NaClO + H2O Carnalite : 3Cl2 + 6NaOH (hot & conc.)  5NaCl + NaClO3 + 3H2O Mother liquor of carnallite contains bromo carnallite KBr MgBr2 . 6H2O. Sea water and mineral springs : Contain NaBr, MgBr2 Cl2 + Ca(OH)2  CaOCl2 + H2O Reaction of F2, Br2, and I2 : The compounds obtained are : CIF, BrCl and ICl3 Reaction with organic compounds : C2H6 + Cl2  C2H5Cl + HCl C2H4 + Cl2  ClCH2– CH2Cl Bromargyrite : AgBr 2. Preparation Laboratory method : Reactants : KBr, MnO2 and conc. H2SO4. 2KBr + MnO2 + 3H2SO4  2KHSO4 + MnSO4 + Br2 + 2H2O The p-Block Elements Liberation of Br2 Using Cl2 gas : Reactants : (KBr, Cl2) or (MgBr2, Cl2) 2KBr + Cl2  2KCl + Br2; MgBr2 + Cl2  MgCl2 + Br2 IODINE 1. Occurrences : Chief sources of iodine are : (i) Sea Weeds : Contain 0.5% of iodine in the form of iodies. (ii) Caliche or crude chile saltpetre : Contains 0.2% of sodium iodate. Commercial method : (a) From carnallite [KCl . MgCl2 . 6H2O] Mother liquor left after the separation of crystals of 2. KCl and MgCl2 contains 0.25% MgBr2 (bittern). This on treating with Cl2 gas Br2 is liberated. (b) From sea water : Sea water contains 0.006% (by weight) of bromine as MgBr2. Here also Br2 can be obtained by passing chlorine gas. 3. * * * Properties : Physical characteristics It is dark–red, poisonous liquid gives brown–red fumes. Boiling point is 59.5ºC, Freezing point is –7.2ºC. Sparingly soluble in water and is soluble in CCl4, CS2, CHCl3 etc. Chemical characteristics : Due to liberation of oxygen it can act as an oxidant and bleaching agent. e.g. SO2 + Br2 + 2H2O  2HBr + H2SO4 ; H2S + Br2  2HBr + S Reaction with NH3 : With cold and dil. NaOH : 3. 2NaOH + Br2  NaBr + NaBrO + H2O * With hot and conc. NaOH : * 6NaOH + Br2  5NaBr + NaBrO3 + 3H2O * 4. Uses of bromine : (i) Used in the form of AgBr as coating on photographic plates, films etc. * (ii) Used in the manufacture of KBr, NaBr (used as a sedative in medicine). * (iii) Used to prepare 1, 2 dibromoethane which is * employed with TEL as an antiknock compound in gasoline. (iv) Used as an oxidant in organic synthesis. Preparation : Laboratory method : Reactants : KI, MnO2 and conc. H2SO4, 2KI + MnO2 + 3H2SO4  2KHSO4 + MnSO4 + 2H2O + I2 Liberation of I2 using Cl2 gas : Reactants : KI and Cl2 2KI + Cl2  2KCl + I2 Commercial methods : From sea weeds : Dry weeds are carefully burnt in shallow pits. The residue called kelp is treated with conc. H2SO4 and MnO2 2NaI + MnO2 + 3H2SO4  2NHSO4 + MnSO4 + I2 From caliche or crude chile salt peter : It contains 0.2% sodium iodate (NaIO3). After removal of NaNO3 from caliche, the mother liquor contains NaIO3. It is treated with calculated quantity of sodium bisulphate to obtain iodine. 2NIO3 + 5NaHSO3  2Na2SO4 + 3NaHSO4 + H2O + I2 Properties : Physical characteristics : Iodine is a dark violet shining solid. Sublimes below its melting point (114ºC) giving violet vapours. Iodine is sparingly soluble in water. In presence of KI, the solubility of iodine increases due to the formagtion of tri iodide ion I– + I2 I3–. Iodine is soluble in organic solvents such as CHCl3, CCl4, CS2 etc. Its vapours are pungent and poisonous to inhale. At high temperature the equilibrium is mainted between molecular and atomic form 1700ºC   I2  I  I . The p-Block Elements Chemical characteristics : Less reactive as compared to Cl2 and Br2. Reaction with H2 and non–metals : Uses of iodine : (i) Used in the preparation of iodoform, iodides, dyes etc. (ii) Used as a laboratory reagent.  H2 + I2  2HI pt 2K + I2  2KI 4. 2P + 3I2  2PI3 Reaction with NaOH : Iodine with cold and dil. NaOH gives sodium hypo iodite (NaOI). With concentrated NaOH iodide (NaI) and idodate (NaIO3) are formed. Reaction with sodium thisulphate : 2Na 2S 2O3 + I2  2NaI + Na2 S 4O 6 (Sodium tetrahionate) (iii) Used in making medicines such as iodex, tincture iodine. (iv) Solution of I2 in KI is used in the treatment of goitre. (v) Used in making photosensitive papers, films etc. BLEACHING POWDER [CaCOCl2] : * It is a mixed salt called calcium chloro hypochlorite. * Proton of HCl and HOCl are cumulatively replaced by calcium [2H+ by one Ca2+] * In fact, bleaching power is a mixture of calcium hypochlorite Ca (OCl)2 4H2O and basic calcium chloride CaCl2.Ca(OH)2 H2O 1. Manufacture : Reactions showing oxidising properties (It is a weak oxidant) Na3AsO3 + H2O + I2  Na3AsO4 + 2HI H2S + I2  2HI + S SO2 + I2 + 2H2O  H2SO4 + 2HI Reaction showing basic character : It shows basic properties and forms I+ and I3+ ions. There are two plants used in the manufacture of bleaching powder. Hasenclever’s plant and Backmann’s Plant (Modern process) Formation of ICl, ICN, INO 2 etc. shows the presence of I+ ICI ICN Basic reaction : When slaked lime [Ca(OH)2 is treated with chlorine at 40ºC results in the formation of bleaching powder. I+ + Cl– I+ + CN– Formation of I (CH3COO)3 and IPO4 etc show the presence of I3+. 2Ca(OH)2 + 2Cl2  Ca(OCl)2 + CaCl2 + 2H2O CaCl2 + Ca(OH)2 + H2O  CaCl2.Ca(OH)2.H2O Reaction with KClO3 and KBrO3 : 2Cl 2 + 3Ca(OH) 2  Ca(OCl) 2 + CaCl 2 . Ca(OH)2.H2O + H2 2KCIO3 + I2  2KIO3 + Cl2 2KBrO3 + I2  2KIO3 + Br2 Bleaching powder is : [Ca(OCl) 2 + CaCl 2 . Ca(OH)2.H2O] Iodine does not liberated Cl2 and Br2 from the corresponding chloride and bromide respectively. Reaction with strong oxidants : 2. Physical characteristics : I2 + 10HNO3  2HIO3 + 10NO2 + 4H2O I2 + 5Cl2 + 6H2O  2HIO3 + 10HCl I2 + H2O + 5O3  2HIO3 + 5O2 Reaction with starch : Iodine turns starch solution blue. Properties : * Bleaching powder is a pale yellow in colour having a strong odour of chlorine. * Soluble in water but clear solution cannot be obtained due to the presence of Ca(OH)2. * It is ionises as : CaOCl2  Ca2+ + Cl– + OCl– The p-Block Elements Chemical characteristics : EXAMPLE : Oxidizing and bleaching action : It loses its oxygen when treated with dilute acid. 2CaOCl2 + H2SO4  CaCl2 + CaSO4 + 2HClO HClO  HCl + [O] nascent oxygen The oxidizing and bleaching action of bleaching powder is due to the formation of nascent oxygen. (1) Evidence for the existence of unipositive ion I+ is : Molten iodine monochloride conducts electricity (2) Reaction : 4KClO3  KCl + 3KClO4 represents : Disproportionation (3) Shapes of chlorate (ClO3–) and perchlorate (ClO4) Oxidizing action : COCl2 + 2KI + 2HCl  CaCl2 + 2KCl + H2O + I2 ions respectively are : Na3AsO3 + CaOCl2  CaCl2 + Na3AsO4 Pyramidal and tetrahedral CaOCl2 + H2S  CaCl2 + H2O + S 3CaOCl2 + 2NH3  3CaCl2 + 3H2O + N2 Bleaching action : Coloured matter + [O]  Colourless matter Reaction with ethylalcohol and acetone : CaOCl .H O 2 2   C2H5OH or CH3COCH3 (4) which hydracid of halogens forms two series of salts. HF (NaHF2 and NaF) (5) In the reaction : Ca(OH)2 + Cl2  ----------- + H2O the unknown compound is : CHCl3 Reaction with dilute acids or acids or CO2 (available chlorine) : Bleaching powder (CaOCl2) (6) The stability oxy halide anion is : ClO– < ClO2– < ClO3– < ClO4– The chlorine obtained from a sample of bleaching powder by treatment with excess of dilute acids or (7) The oxidising power of oxy acids is : CO2 is called available chlorine : HClO > HClO2 > HClO3 > HClO4 COCl2 + 2HCl  CaCl2 + H2O + Cl2 (8) I2 is liberated from HI by the halogens : CaOCl2 + H2SO4  CaSO4 + H2O + Cl2 F2, Cl2 and Br2 CaOCl + CO  CaCO + Cl 2 2 3 2 Reaction in presence of CoCl2 2CaOCl2 3. 2CaCl2 + O2 Uses of bleaching powder : 2HI + F2 (Cl2, Br2)  2HF (HCl, HBr) + I2 (9) Which silver halide is insoluble in ammonia AgI (i) Used in the sterilization of drinking water (disinfectant (10) HBr and HI cannot be prepared by treating and germicide) corresponding bromide and iodide with H2SO4. (ii) Used as bleaching agent for cotton, linen and wood HBr and HI are strong reductants and reduce pulp. (iii) Used for the commercial preparation of chloroform. H2SO4 to SO2 and get themselves oxidized to (iv) Used as an oxidizing agent in industry. Br2 and I2 respectively.