化学竞赛 杂化轨道理论1.ppt

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1、18.1 Theory of hybrid orbital 杂化轨道理论杂化轨道理论分子轨道理论价键理论化学键理论价电子离域价电子定域在两原子之间或成为孤对电子每个原子提供一个价电子和一个轨道重叠成键Each bondarisesfromtheoverlapofanH1sorbitalwithoneoftheO2porbitals.Thismodelsuggeststhatthebondangleshouldbe90,whichissignificantlydifferentfromtheexperimentalvalue.104.5 C2vOHH2s2pPureporbitals2s2pO2

2、HHH2 2OOOHHWhy do atomic orbital need hybridization?为什么要杂化？spsp3 32s2pO2HO*sp3Linus PaulingLinus PaulingHybridization(1931)Hybridization(1931)Simplified MO diagram of diatomic molecules Simplified MO diagram of diatomic molecules 分子轨道理论分子轨道理论分子轨道理论分子轨道理论 Energy2s2s1g1u2p2p2g2u1u1gpzHOMOLUMON2:KK(3)2

3、(4)2(1)4(5)2Hybridization of 2s and 2p 2s Hybridization of 2s and 2p 2s 和和和和2p2p的杂化的杂化的杂化的杂化Boundary surfaces ofBoundary surfaces of (a)2s+2p(a)2s+2p(b)2s-2p(b)2s-2pEnergy diagram for XEnergy diagram for X2 2:(a)with hybridization and(b):(a)with hybridization and(b)without 2s-2pwithout 2s-2pz z hybr

4、idization.The 1s orbitals are left out.hybridization.The 1s orbitals are left out.(a)(a)(b)(b)2.Constructionofhybridorbitals杂化轨道的构造If we begin with n AOs,we must end up with n orbitals after hybridization.n 个原子轨道杂化得到 n 个杂化轨道 All n hybrids are equivalent except for directionality same energy.所有的杂化轨道能

5、级相同，但方向不同a.sp hybridization(linear species)sp杂化，直线型OnesandonepAOmixtoformasetoftwohybridorbitals.sp,=180,linear,Normalizationandorthogonality1s 1s2 HHybridizationThe promotion energy can be considered a part of the energy required to form hybrid orbitals.The overlap of the hybrid orbitals on Be with

6、 the 1s orbitals on the H atoms gives two Be-H(sp)-1s bonds oriented 180from each other.Be*(sp)2s2pBeBe*BeH2sp2pOne s and two p(px and py)AOs mix to form a set of three hybrid orbitals.b.sp2 hybridization(trigonal planar)sp2杂化，平面三角形sp2,D3h,=120,triangular,f=1.991，=1/3h1h2h3xyA trigonal planar molecu

7、le and sp2 hybridization:the bonding in BH32s2pBB*BH3sp2 hybridp orbital1s 1s 1s3 HB*sp22ph1h2h4h3zOne s and 3 p AOs mix to form a set of four hybrid sp3 orbitals.c.sp3 hybrides(tetrahedral)sp3杂化，四面体CH42s2p1s 1s 1s 1sC4 HC*sp3C*(sp3)Thisgivesfoursp3orbitalsthatareorientedinatetrahedralfashion.Theove

8、rlapofthesp3hybridorbitalsonCwiththe1sorbitalsontheHatomsgivesfourC-H(sp3)-1sbondsoriented109.5fromeachother.h1h2xyh3h4h5zd.dsp3(sp3d)hybrides(trigonal bipyramidal)dsp3(sp3d)杂化，三角双锥The bond lengths will not be the same because there is more d contribution to the axial hybrid orbitals.h1h2xyh3h4h5zTh

9、e bond lengths will not be the same because there is more d contribution to the axial hybrid orbitals.平面和轴向轨道是不等价的。In the case dsp3,the axial bond length is shorter,While it is longer in the case sp3d（dsp3 杂化轴向键长较短，sp3d杂化则较长 PF53s3pPP*3dP*(sp3d)3dWe need hybrid orbitals suitable for bonds to 5 atoms

10、.ns and np combinations can only provide four,so we need to use nd orbitals(if they are available).3dz23pz3py3px3ssp3dz2The appropriate mixture to form a trigonal bipyramidal arrangement of hybrids involves all the ns and np orbitals as well as the ndz2 orbital.Valence bond theory treatment of a tri

11、gonal bipyramidal molecule:the bonding in PF5F2s2pF2s2pF2s2p3dP*(sp3d)F2s2pF2s2pThe overlap of the sp3d hybrid orbitals on P with the 2p orbitals on the F atoms gives five P-F(sp3d)-2p bonds in two sets:the two axial bonds along the z-axis(180 from each other)and three equatorial bonds in the xy pla

12、ne(120 from each other and 90 from each axial bond).This means that the 5 bonds are not equivalent!Square planar:D4hh1xyh3h2h4Eg.Ni(CN)42-e.dsp2 hybrides(square planar)dsp2杂化，平面四边形512346xyzf.d2sp3(sp3d2)hybrides(Octahedral)d2sp3(sp3d2)杂化，八面体SF6The overlap of the sp3d2 hybrid orbitals on S with the 2

13、p orbitals on the F atoms gives six S-F(sp3d2)-2p bonds 90 from each other that are equivalent.You can figure out the normalization coefficients.3dz23pz3py3px3ssp3d23dx2-y23s3pSS*3dS*(sp3d2)3dFF FFF FHybridization schemesspndm gives a“complete”set of hybrid orbitals for“any”geometry.spLinear 直线sp2Tr

14、igonal planar 平面三角形sp3Tetrahedral 四面体sp3d(dz2)Trigonal bipyramidal三角双锥sp3d(dx2-y2)square-based pyramidal四方锥sp3d2 Octahedral八面体sp2dSquare planar平面四边形 Valence bond theory treatment of-bonding -键的价键理论处理sp2pC*(sp)O2s2pO2s2p2s2pCThe overlaps of the sp hybrid orbitals on C with the two 2p orbitals on O gi

15、ve the two bonds and it is the overlaps of the“left over”p orbitals on C with the appropriate p orbitals on O that form the(2p-2p)bonds between each two atoms.OCOValence bond theory treatment of-bonding:the bonding in etheneThere are three“objects”around each C so the geometry is trigonal planar at

16、each carbon.The shape is given by AX3 for each carbon.2s2pEach Csp22pC*(sp2)1s 1s1s1s4 Hsp22pC*(sp2)Each C*The overlap of the sp2 hybrid orbitals on C with the the 1s orbitals on each H give the four terminal(sp2-1s)bonds.The double bond between the C atoms is formed by a(sp2-sp2)bond and the(2p-2p)

17、bond.Valence bond theory treatment of-bonding:the bonding in the nitrate anionThere are three“objects”around N so the geometry is trigonal planar.The shape is given by AX3(trigonal planar).2s2pNN+O-2s2pO-2s2pO2s2psp22pN+*(sp2)The overlap of the sp2 hybrid orbitals on N with the the 2p orbitals on th

18、e O give the three(sp2-2p)bonds and it is the overlap of the“left over”p orbital on N with the appropriate orbital on the uncharged O atom that forms the(2p-2p)bond.N NN N价键理论 共振结构VBT gives only one of the canonical structures at a time.分子轨道理论离域分子轨道理论离域分子轨道理论离域分子轨道理论离域p p p p键键键键MO gives delocalized

19、 MO gives delocalized p p p p-orbital-orbitalC C6 6H H6 6(benzene)(benzene)-bonds-bondsEachCusesspEachCusessp2 2orbitalstoform3orbitalstoform3-bonds-bonds1porbitaloneachCremains1porbitaloneachCremains价键理论共振结构价键理论共振结构 C C6 6HH6 6(benzene)delocalized (benzene)delocalized p p p p-bonds-bonds 分子轨道理论离域分子

20、轨道理论离域分子轨道理论离域分子轨道理论离域p p p p键键键键s s s s frame work frame workp p p p resonance resonanceDelocalizedbond离域键Conditionsthatfavortheformationofdelocalizedbondi.Theatomsarecoplanar,witheveryatomcontributingap-orbitalorientatedinthesamedirection.原子共平面，每个原子提供一个同取向的p轨道ii.Thenumberofelectronsislessthantwice

21、thenumberoftheparticipatingp-orbitals.电子数小于轨道数2被n-orbitalnumbers,m-electronnumbers(n2)DelocalizedbondPhenolphthaleinisanorganiccompound(C20H14O4)usedasanacid-baseindicator.Thecompoundiscolorlessinacidicsolutionandpinkishinbasicsolution(withthetransitionoccuringaroundpH9).酚酞变色原因sp2pC*(sp)O2s2pO2s2p2s

22、2pCOCO18.2 Structure of ABn Molecules（Abn分子的结构）分子的结构）1.AB2valence electron 6+7x2=20H2O,H2Svalence electron 8i.Nonlineartype(bent)(20valenceelectron)ex.OF2,OCl2,SCl2,TeBr2O:sp3hybridizationii.Nonlineartype(bent)(1719valenceelectron)ex.18O3(valenceelectron)O:sp2hybridization+pzOOO.pz sp2 orbitalpzpzan

23、ti-bondingnon-bondingbondingIsoelectron analogy:SO217 valence electron NO219 valence electron ClO2.iii.Lineartype(AB216valenceelectron)CO2C:sphybridization+px+py,Isoelectronanalogy:CO2,NO2+,N2O,N3-,COS,BeCl2,HgCl2iv.Lineartype(AB222valenceelectron)ICl2-XeF2sp3dhybridization18.2 Structure of ABn Mole

24、cules2.AB3i.TrigonalPyramidaltype(8,or26valenceelectron)ex.NH3,PF3,PCl3,AsCl3sp3hybridizationii.Trigonalplanartype(6,24valenceelectron)Centric atom B:sp2 hybridization 24-6 18-12 6Isoelectron analogy:AlF3,NO3-,CO32-,SO3,Cl2CO,(H2N)2C=O,Cl2C=Santi-bondingnon-bonding bondingForfouratomangulartypemolec

25、ulars,formingonebonding,twononbondingandoneantibondingorbitals,ingeneralExample:BH3ex.BF3,NO3-,CO32-,SO3sp23 sp2 hybrid orbitals each with one electron.This one electron pairs with the hydrogen electron.ii.Trigonalplanartype(6,24valenceelectron)ex.ClF3,BrF3,sp3dhybridorbitalsiii.Ttype(28valenceelectron)18.2 Structure of ABn Molecules3.AB4TetragonalPyramidaltypeex.CH4,NH4+,CCl3sp3hybridizationdp-bondex.PO4 3-,SO42-dxzpzxxpx