無機化學課件：23 Group VIIA VIIIA

1、Halogensgroup 17Fluorine, Chlorine, Bromine, Iodine, Astatine SymbolFClBrIElectronic Configuration2s22p5 3s23p5 4s24p5 5s25p5 Major Oxidation Number1,0 1,0,+1,+3, +4,+5,+7 1,0,+1,+3,+5,+7 1,0,+1,+3,+5,+7Electron Affinity/(kJ mol1 )322348.7324.5295Dissociation Energy of X2/（kJ mol1）155240190149Electr

2、onegativity (Pauling)3.963.162.962.66General PropertiesPhysical Properties：Stateg g l sb.p./-188 -34 59 185 m.p. /-220 -102 -7 114ColorPale Yellowish Brown PurpleYellow GreenIntermolecular ForcesSmallLargeF2 Cl2 Br2 I2The ElementsF2 Cl2 Br2 I2X2 oxidant：SWX- reductant：WS RedoxStrongest Oxidant: F2，S

3、trongest Reductant I。Chemical Properties of the Halogens2.8891.3601.07740.5345：/V)/XX(2-Conclusion：F2+NaOH NaF+OF2+H2O （CN)2+2NaOHNaCN+NaOCN+H2OCl2+2NaOH NaCl+NaClO+H2OBr2+NaOH50 oC NaBr+NaBrO3+H2O0 oC NaBr+NaBrO+H2O3I2+6NaOH5NaI+NaIO3+3H2O 80oC3Cl2+6NaOH 5NaCl +NaClO3+ 3H2OProportionation：The major

4、ity exists as elements in aqueous solutions Reaction with H2O：Oxidation：2KMnO4+2KF+10HF+3H2O2 = 2K2MnF6+8H2O+3O2 SbCl5+5HF = SbF6+5HCl K2MnF6+2SbF5 423K 2KSbF5+MnF4 MnF3+1/2F2 (Oxidation)F2 (g) Electrolysis： Cl2 (g)Preparation of the Elements：+HFLab：Industrial：Br2(l)oxidant：(Reverse Proportionation)

5、I2 (s)From seaweed ：Purification：+-+12H10Cl2IOI2)(5ClO6H322excessO2HIMn2I4HMnO2222+- Ambient T，colorless, pungentHFHClHBrHIDec Tond E/kJmol-1570432366298AcidityWeakStrongpolarity bp stability mp*-83.57-114.18-86.87-50.80m.p./* 19.52-85.05-66.71-35.1b.p./6.373.572.761.40/(10-30cm)Hydroge

6、n Halides-271.1-92.3-36.4-26.5/kJmol-11.Properties in dilute solution： in not-so-dilute solution, HF exists as dimer (HF)2：H2F2H+HF2F+HF HFH+FHF2Ka = 6.6104 Ka = 5SiO2 +4HF = 2H2O+SiF4 CaSiO3+6HF = CaF2+3H2O+SiF4 HF reacts with SiO2 and silicates, etching glass SiF62- in aqueous solution HX polar，ea

7、sily dissolvable in H2O. 273K，1m3 dissolve 500m3 HCl，HF miscible with H2O. forms azeotropic solution with water HF in solid state:HClHFmetathesismetathesisIndustrial：Lab：2.Preparation of hydrogen halidesHydrolysis of halidesHBr & HI(X=Br,I)No metathesisActualMetathesis with other acid? Intermolecula

8、r Forces: Dispersion Forcenon-polarEasily dissolvable in organic solvents, not much in H2O I2 easily dissolvable in KI、HI and aqueous solution of other iodide solution：I2 I I3 K725 I3 (I2)n(I)-3Ilinear-PolyhalidesMolecular Orbital Theory I3-II - IThe linear I3- molecule, with Dh symmetry, is an exam

9、ple of 3c-2e bonding. I3- has 22 valence electrons and all but one of the MOs are filled (only the su* orbital is empty). A partial MO diagram, with only the interactions of the Xe 5pz orbital and the LGOs derived from the F 2pz orbitals (su and sg) shown, may be constructed to illustrate the 3c-2e

10、bonding.Twenty electrons are found on the outer iodines (14 e-) or central iodine (6 e-) centered non-bonding MOs, which may be treated as lone pairs of electrons. The remaining 2 electrons are found in bonding su MO, such that I3- has a bond order of and the bonding may be described as 3c-2e bondin

11、g.Note that I3- is isoelectronic with XeF2, one of the few known rare gas compoundsPolyhalogen cationsPolyhalogen cations, such as Br2+, I2+, Cl3+, Br3+, I3+, Br5+, I5+, and I42+ are well known, and prepared the dihalogens X2 using strong oxidants. In the X2+, the removal of a p* electron shortens t

12、he bond (increases the bond order to 1.5) in Br2+ to 215 pm (vs 227 pm in Br2) and in I2+ to 258 pm (vs 272 pm in I2)In the X3+, the cations are bent, with similar X-X distances as in X2.The I42+ cation is a “rectangular” dimer of I2+, with I-I distances of 258 and 326 pmXInterhalogensThe interhalog

13、ens are a large group of compounds containing combinations of different halogen atoms, such as ClF3 or I2Cl6.They are all prepared by direct combinations of the elements, with the product distribution controlled by temperature and the relative amounts of the halogens used. In general lower tempertur

14、es give lower oxidation states of the central atom, while higher oxidation states are achieved by raising the temperature of the reaction. Other features are: F is always in the oxidation state of -1 the highest oxidation states for X reached are Cl Br I the highest oxidation states are achieved in

15、combination with fluorineInterhalogensInterhalogensThe interhalogens tend to be good oxidizing agents, and most are fluorides. These interhalogens, XFn, are good fluorinating agents. UF4(s) + ClF3(g) UF6(s) + ClF(g)The highest oxidation state for the central atom X is found in IF7, as the smaller ha

16、logens are not large enough to accommodate more than 5 fluorides, with the large interfluoride lone pair repulsions.While ClF3 and BrF3 are T-shaped, ICl3 dimerizes to form I2Cl6In I2Cl6 each I atom has two “axial” lone pairs, such that the molecule is planar, with D2h symmetry Hypofluorous acid HOF

17、 For fluorine, the only known oxoacid is hypofluorous acid, HOF, in which fluorine is in the +1 oxidation state. It can be made by passing F2 gas over ice at -40 C and collecting the HOF gas which condenses. It decomposes at room temperature to form HF and O2F2 + H2O HOF + HFInstead of ionizing in w

18、ater, it reacts with water to form hydrogen peroxide and hydrogen fluoride.HOF + H2O H2O2 + HFHalogen oxoacidsOxoacids of chlorineOxoacids of bromineOxoacids of iodineHypochlorous acid (Cl +1)HOClHypobromous acidHOBrHypoiodous acidHOIChlorous acid(Cl +3)HOClO (HClO2)Chloric acid(Cl +5)HOClO2 (HClO3)

19、Bromic acidHOBrO2 (HBrO3)Iodic acidHOIO2 (HIO3)Perchloric acid(Cl +7)HOClO3 (HClO4)Perbromic acidHOBrO3 (HBrO4)Periodic acidOrtho-periodic acidHOIO3 (HIO4)(HO)5IO(H5IO6)Hypohalous acids HOX HOXHOClHOBrHOIpKa4.53 8.6910.64The hypohalous acids (HOX) are known for each halogen (HOF described before) an

20、d for X = Cl, Br, and I, can be made by the reaction of the halogen with mercuric oxide.2 X2 + 3 HgO + H2O Hg3O2X2 + 2 HOXThese acids cannot be isolated, but in aqueous solution they behave as weak acids.hypohalorous acid and hypohalogeniteHClO HBrO HIOacidityOxidizing powerstability：stableless stab

21、le2.810-5 2.610-9 2.410-111.495 1.3410.983)/VX/XO(-Hypohalite anions Hypochlorite salts can be isolated with cations such as Na+, K+, and Ca2+ . Sodium hypochlorite, NaOCl, is a bleaching agent (pool bleach) and disinfectantHypohalites are powerful oxidizing agents (Eo = 1.61 V for HOCl, 1.58 V for

22、HOBr, and 1.44 for HOI)2 HOX + 2e- + 2 H+ X2 + 2 H2OHypohalite anions The hypohalites are all unstable with respect to disproportionation. At room temperature, this process is slow for HOCl, fast for HOBr, and very fast for HOI. The products are the halate anions (XO3-) and the halide (X-)3 NaOCl Na

23、ClO3 + 2 NaClWhy are the hypohalites unstable with respect to disproportionation? We can look at the thermodynamics of the process, using the reduction potentials for the various halogen species in solution.Important RXNs：bleaching powderHalogen oxoacids and oxoanions Hypohalite disproportionation:3

24、 OX- XO3- + 2 X- (X +1) (X +5) (X -1)which is made up of:OX- + 2 H2O XO3- + 4 e- + 4H+OX- + 2 H+ + 2 e- 2 X- + H2O Halic acids, HXO3 The halic acids, HXO3, are strong acids (pKa 0 for X = Cl and Br, and 0.77 for X = I), but only HIO3 can be isolated, as a stable white solid. The halic acids are prep

25、ared by:Ba(XO3)2 + H2SO4 BaSO4 + 2 HXO3 (X = Cl or Br)I2O5 + H2O 2 HIO3The HIO3 is stabilized in the solid state by considerable H bondingHalic Acids and HalatesHalic acid： HClO3 HBrO3 HIO3acidity： S S M 1.458 1.513 1.209Cmax Obtained：40% 50% crystalStability：highlow)/VX/XO(2-3Halate anions The hala

26、te anions, XO3-, have a number of uses:ClO3- strong oxidizing agent, used as a weedkiller and in the manufacturing of ClO2, and in fireworks and safety matchesBrO3- and IO3- are used in volumetric analyses IO3- + 5 I- + 6 H+ 3 I2 + 3 H2OPotassium chlorate The gritty material on the side of a match-b

27、ox is coated with red phosphorus. The match-head contains potassium chlorate and some red colouring. When the match-head rubs against the box, friction ignites the mixture of phosphorus and potassium chlorate. Potassium chlorate By separating the strong oxidizer (potassium chlorate) from the reducer

28、 (phosphorus) the matches are prevented from igniting spontaneously.Perhalic Acids and PerhalatesHClO4 HBrO4 H5IO6Acidity：strongest strong weak1.226 1.763 1.60All are strong oxidizing agents, stable pure form 4-=)104.4(HIO4)/V/XO(XO34- O40% max solutionMay obtainsolid1.495 1.55 1.451.409Oxidizing po

29、wer (except HClO2)Oxo acids of chlorineHClO HClO2 HClO3HClO4Acidity：Stability：/V)X/(-oxlow low relatively SStableOxo acids and their sodium saltsacidStability & acidityoxidantsaltstabilityOxidant basicity+1HOCl NaClO +3HOCl2 NaClO2 +5HOCl3 NaClO3 +7HOCl4 NaClO4 stabiltyoxidantImportant RXN：Periodic

30、acids and anions The equilibria between different forms of periodic acids an anions is quite complex:H3IO62- + H+ HIO4- + 2H2O2 H3IO62- 2 HIO52- + 2 H2O2 HIO52- H2I2O104- I2O94- + H2OStructure of oxoacidsIdentification of I-、Br- mixtureTHE NOBLE GASESGROUP 18helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn)Rare Gases, Inert GasesGroup 8A The Noble GasesDiscoveryHe: 1868 by P Janssen & J N Lockyer discovered while looking at the chr