化学竞赛杂化轨道理论

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 bond arises from the overlap of an H1s orbital with one of the O2p orbitals. This model suggests that the bond angle should be 90, which is significantly different from the experimental value. 1

2、04.5 C2vOHH2s2pPure p orbitals2s2pO2HOHHWhy do atomic orbital need hybridization?为什么要杂化？2s2pO2HO* sp3Energy2s2s1g1u2p2p2g2u1u1gpzHOMOLUMON2: KK(3)2 (4)2 (1)4 (5)2)()2(22sBsAgs)()2(22BpApzgzzp)()()()()2(22212221222221BpsBApsABpApsBsAgzzzzccccccs)()()()()2(22212221222221BpsBApsABpApsBsAgzzzzccccccs)(2

3、221ApsAzcc)(2221ApsAzcc2s2p2p12212p2p2s2s2p2. Construction of hybrid orbitals 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. 所有的杂化轨道能级相同，但方向不同pzpypxshcccc24232221a. sp hybridiz

4、ation (linear species) sp杂化，直线型 One s and one p AO mix to form a set of two hybrid orbitals.)(21)(212221pxshpxshsp, =180, linear, Normalization and orthogonality1s 1s2 HHybridizationThe promotion energy can be considered a part of the energy required to form hybrid orbitals.BeHHThe overlap of the hy

5、brid orbitals on Be with the 1s orbitals on the H atoms gives two Be-H (sp)-1s bonds oriented 180from each other. Be* (sp)2s2pBeBe*BeH2sp2ppypxshpypxshpxsh223222212161312161313231 One 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，

6、平面三角形sp2, D3h, =120, triangular, f=1.991， =1/3h1h2h3xyA trigonal planar molecule and sp2 hybridization: the bonding in BH32s2pBB*BHHHxy120BH3sp2 hybridp orbital1s 1s 1s3 HB*sp22ph1h2h4h3zz)(-x,-y, along 221zyxhpppsz)y,(x, along 121zyxhppps(x,-y,-z) along 214hzyxpppsy,-z)(-x, along 321zyxhppps One s

7、and 3 p AOs mix to form a set of four hybrid sp3 orbitals.sp3 hybrides (tetrahedral) sp3杂化，四面体34244444,POSOPXGeHSiHCHCH42s2p1s 1s 1s 1sC4 HC*sp3C* (sp3)This gives four sp3 orbitals that are oriented in a tetrahedral fashion. The overlap of the sp3 hybrid orbitals on C with the 1s orbitals on the H a

8、toms gives four C-H (sp3)-1s bonds oriented 109.5 from each other. PFFFFFyxhyxhxhppsppsps2161312161313231321h1h2xyh321212254zzhzzhdpdph4h5zSFFFFdsp3 (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

9、 orbitals.PFFFFFyxhyxhxhppsppsps2161312161313231321h1h2xyh321212254zzhzzhdpdph4h5zThe 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

10、短， sp3d杂化则较长 PF53s3pPP*3dP* (sp3d)3dWe need hybrid orbitals suitable for bonds to 5 atoms. 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 a

11、ll the ns and np orbitals as well as the ndz2 orbital.yzx12345Valence bond theory treatment of a trigonal 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

12、 sets: the two axial bonds along the z-axis (180 from each other) and three equatorial bonds in the xy plane (120 from each other and 90 from each axial bond). This means that the 5 bonds are not equivalent!Square planar: D4h222222222121212121212121212121214321yxpyshyxpyshyxpxshyxpxshdddd yxyxppsd,2

13、2 h1xyh3h2h4Eg. Ni(CN)42-dsp2 hybrides (square planar) dsp2杂化，平面四边形512346xyz23121615zzdpsoc2221212121611zyxxddpsoc2221212121612zyxyddpsoc2221212121613zyxxddpsoc2221212121614zyxyddpsoc23121616zzdpsoczyxyxzpppsdd,222d2sp3 (sp3d2) hybrides (Octahedral) d2sp3 (sp3d2)杂化，八面体SFFFFFFSF6The overlap of the sp

14、3d2 hybrid orbitals on S with the 2p 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 or

15、bitals for “any” geometry.spLinear 直线sp2Trigonal 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 or

16、bitals on C with the two 2p orbitals on O give 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.OCOCOOValence bond theory treatment of -bonding: the bonding in etheneThere are three “object

17、s” around each C so the geometry is trigonal planar at each carbon. The shape is given by AX3 for each carbon.CCHHHH2s2pEach 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 bo

18、nd between the C atoms is formed by a (sp2- sp2) bond and the (2p-2p) bond.Valence bond theory treatment of -bonding: the bonding in the nitrate anionONOOThere are three “objects” around N so the geometry is trigonal planar. The shape is given by AX3 (trigonal planar).2s2pNN+O-2s2pO-2s2pO2s2psp22pN+

19、*(sp2)The overlap of the sp2 hybrid orbitals on N with the the 2p orbitals on the 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.NOOO64价键理论 共振结构VBT gives only one of the canonica

20、l structures at a time.NOOONOOONOOOHHHHHHHHHHHH66Delocalized bond 离域键Conditions that favor the formation of delocalized bond i. The atoms are coplanar, with every atom contributing a p-orbital orientated in the same direction. 原子共平面，每个原子提供一个同取向的p轨道ii. The number of electrons is less than twice the n

21、umber of the participating p-orbitals. 电子数小于轨道数2被mn n-orbital numbers, m-electron numbers (n2)NOOO sp2N sp2C sp2109NHHN sp2C sp287HHN sp2C sp266NunfavorableDelocalized bondPhenolphthalein is an organic compound (C20H14O4) used as an acid-base indicator. The compound is colorless in acidic solution a

22、nd pinkish in basic solution (with the transition occuring around pH 9). 酚酞变色原因 HOCOHCOOHOCOCOONaNaOHH2Osp3sp2sp2pC*(sp)O2s2pO2s2p2s2pCOCOCOO43COO18.2 Structure of ABn Molecules （Abn分子的结构）分子的结构）1. AB2valence electron 6 + 7x2 = 20 H2O, H2Svalence electron 8i. Non linear type(bent) (20 valence electro

23、n) ex. OF2 , OCl2, SCl2, TeBr2O: sp3 hybridizationii. Non linear type(bent) (1719 valence electron) ex. 18 O3 (valence electron) O: sp2 hybridization + pzbonding-anti bonding-non bonding 3211212321122121221OOO.pz sp2 orbitalpzpz43 48-6-18 :electrons 43anti-bondingnon-bondingbondingIsoelectron analog

24、y: SO217 valence electron NO219 valence electron ClO2533343.iii. Linear type (AB2 16 valence electron) CO2 C: sp hybridization +px +py, bonding-anti )2(2) 1 (21bonding-non )2() 1 (21bonding )2(2) 1 (21321OCOOOOCOIsoelectron analogy : CO2, NO2+, N2O, N3-, COS, BeCl2, HgCl2OCO434343 , :284-4-16 :electrons yx321iv. Linear type (AB2 22 valence electron) ICl2- XeF2sp3d hybridization18.2 Structure of ABn Molecules2. AB3i. Trigonal Pyramidal type (8, or 26 valence electron) ex.