化学竞赛杂化轨道理论1.ppt

18.1 Theory of hybrid orbital 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.,Pure p orbitals,Why do atomic orbital need hybridization?为什么要杂化？,Linus Pauling,Hybridization (1931),Simplified MO diagram of diatomic molecules 分子轨道理论,Energy,2s,2s,1g,1u,2p,2p,2g,2u,1u,1g,pz,HOMO,LUMO,N2: KK(3)2 (4)2 (1)4 (5)2,Hybridization of 2s and 2p 2s 和2p的杂化,Boundary surfaces of (a) 2s+2p (b) 2s-2p,Energy diagram for X2: (a) with hybridization and (b) without 2s-2pz hybridization. The 1s orbitals are left out.,(a),(b),2. 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,a. sp hybridization (linear species) sp杂化，直线型,One s and one p AO mix to form a set of two hybrid orbitals.,sp, =180, linear, Normalization and orthogonality,Hybridization,The promotion energy can be considered a part of the energy required to form hybrid orbitals.,The overlap of the hybrid orbitals on Be with the 1s orbitals on the H atoms gives two Be-H (sp)-1s bonds oriented 180from each other.,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，平面三角形,sp2, D3h, =120, triangular, f=1.991， =1/3,A trigonal planar molecule and sp2 hybridization: the bonding in BH3,BH3,sp2 hybrid,p orbital,h1,h2,h4,h3,z,One s and 3 p AOs mix to form a set of four hybrid sp3 orbitals.,sp3 hybrides (tetrahedral) sp3杂化，四面体,CH4,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 atoms gives four C-H (sp3)-1s bonds oriented 109.5 from each other.,x,y,h4,h5,z,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.,x,y,h4,h5,z,The 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,PF5,Valence bond theory treatment of a trigonal bipyramidal molecule: the bonding in PF5,Square planar: D4h,h1,x,y,h3,h2,h4,Eg. Ni(CN)42-,dsp2 hybrides (square planar) dsp2杂化，平面四边形,5,1,2,3,4,6,x,y,z,d2sp3 (sp3d2) hybrides (Octahedral) d2sp3 (sp3d2)杂化，八面体,SF6,The overlap of the sp3d2 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.,Hybridization schemes,spndm gives a “complete” set of hybrid orbitals for “any” geometry.,Valence bond theory treatment of p-bonding p-键的价键理论处理,sp,2p,C*(sp),O,2s,2p,O,2s,2p,2s,2p,C,The overlaps of the sp hybrid orbitals 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) p bonds between each two atoms.,Valence bond theory treatment of p-bonding: the bonding in ethene,There are three “objects” around each C so the geometry is trigonal planar at each carbon. The shape is given by AX3 for each carbon.,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) p bond.,Valence bond theory treatment of p-bonding: the bonding in the nitrate anion,There are three “objects” around N so the geometry is trigonal planar. The shape is given by AX3 (trigonal planar).,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) p bond.,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p键 MO gives delocalized p-orbital,C6H6 (benzene) -bonds,Each C uses sp2 orbitals to form 3 -bonds 1 p orbital on each C remains 价键理论共振结构,C6H6 (benzene) delocalized p-bonds 分子轨道理论离域p键,s frame work,p resonance,Delocalized 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 number of the participating p-orbitals. 电子数小于轨道数2被,n-orbital numbers, m-electron numbers (n2),Delocalized bond,Phenolphthalein is an organic compound (C20H14O4) used as an acid-base indicator. The compound is colorless in acidic solution and pinkish in basic solution (with the transition occuring around pH 9). 酚酞变色原因,sp,2p,C*(sp),O,2s,2p,O,2s,2p,2s,2p,C,18.2 Structure of ABn Molecules （Abn分子的结构）,1. AB2,valence electron 6 + 7x2 = 20,H2O, H2S,valence electron 8,i. Non linear type(bent) (20 valence electron) ex. OF2 , OCl2, SCl2, TeBr2,O: sp3 hybridization,ii. Non linear type(bent) (1719 valence electron) ex. 18 O3 (valence electron) O: sp2 hybridization + pz,pz,sp2 orbital,pz,pz,iii. Linear type (AB2 16 valence electron) CO2 C: sp hybridization +px +py,Isoelectron analogy : CO2, NO2+, N2O, N3-, COS, BeCl2, HgCl2,iv. Linear type (AB2 22 valence electron) ICl2- XeF2,sp3d hybridization,18.2 Structure of ABn Molecules,2. AB3,i. Trigonal Pyramidal type (8, or 26 valence electron) ex. NH3 , PF3, PCl3, AsCl3,sp3 hybridization,ii. Trigonal plana