杂化轨道英文版.ppt

1、5.3&5.4 Valence Bond TheoryHybrid Atomic Orbital Model and Its Application,Hybrid Atomic Orbital Model 杂化轨道理论 杂化方式与C-C、C-H键长 价电子对互斥理论与分子的几何构型 Valence Shell Electron Pairs Repulsion (VSEPR),1. Hybrid Atomic Orbital Model （杂化轨道理论）,Localization of A Chemical Bond,Similar values of Bond Length(pm) and B

2、ond Energies(KJ/mol),Localization of A Chemical Bond,Similar values of Bond Angles,Concept of Chemical Bond,The molecular stabilities might come from the formation of the valence bond orbitals, each of which can hold a pair of anti-parallel spin electrons. This is the origin of chemical bond.,The el

3、ectrons in a valence bond orbital are localized rather than delocalized.,Lewis Structures,Bond Angles and Atomic Orbital Hybridizations,sp,sp2,sp3,Direction of A Hybrid Atomic OrbitalThrough Linear Combination of p Orbitals,p = a px + b py + g pz,If p is normalized, then,杂化轨道的方向余弦,px,py,pz,p,cos-1a,

4、cos-1b,cos-1g,Complete Form of Hybrid Atomic Orbitals与s轨道的混合,Suppose there is two hybrid Atomic orbitals,la = lb,la lb,ha,hb,ha,hb,Equivalent hybridization 等性杂化,Non-Equivalent hybridization 不等性杂化,Normalization of A Hybrid Atomic Orbital,Orthogonal,Normalized,Orthogonality of Hybrid AOs,If a b,Bond A

5、ngles Between Two Hybrid AOs,For equivalent hybridizations:,sp (pz),Linear,sp2 (px, py),Planar Triangle,sp3 (px, py , pz),Tetrahedral,Hybrid AO: sp杂化,sp (pz),Linear,x,y,z,x,y,z,pb = -pz,x,y,z,ha,hb,Hybrid AO: sp2杂化,sp2 (px, py),Planar Triangle,y,x,pa,pb,pc,a = a, b, c,y,x,ha,hb,hc,Transformation Mat

6、rix,HAO and SALC Transformation Matrices,Hybridization Transformation Matrix,SALC of 3H in BH3 Transformation matrix,S,ST,Transposition of S 转置矩阵,S ST = I,Localized Molecular Orbital,Localized molecular orbital in BH3,Localized Equivalent Orthonormalized Double occupied,These LMOs have the propertie

7、s,Hybrid AO: sp3杂化,sp3 (px, py , pz),Tetrahedral,y,z,a,b,c,d,x,a = a, b, c, d,Transformation Matrix,2. 杂化方式与C-C、C-H键长,List of C-C and C-H Bond Lengths,C2H2(120pm) C2H4(134pm) C2H6(154pm),3.价电子对互斥理论与分子的几何构型 Valence Shell Electron Pairs Repulsion (VSEPR),To Explain the Bond Angles,Electron negativity

8、decreasing,To Explain the Geometry of Noble-gas Compounds,First compound: Xe(PtF6)x (x=12)， a red crystalline solid Neil Bartlett produced (1962) Other compounds: XeF2, XeF4 (most stable), and XeF6 Unstable Compounds: XeO3 and XeO4, explosively unstable. Xenate salts : Na4XeO6 8H2O，Cs2XeF8,To explai

9、n,NF3 FNF = 102.1 NCl3 ClNCl = 104 NBr3 BrNBr = 107.6 NH3 HNH = 106.7,Valence Shell Electron Pairs Repulsion Model,VSEPR,Electron Localization (VB Model),E = EA + EB + EC + + EAB + EAC + EBC + ,Energy of Electron Pairs,Pair-Pair Interactions,The VSEPR model assuming that: the valence shell electron

10、pairs are arranged as far from one another as possible.,Steps to Decide the Molecular Geometry, Draw the Lewis structure Determine how many electrons pairs are around the central atom. Count a multiple bond as one pair. Arrange the electrons pairs.,Molecular Geometry and Electron Pair Numbers,In the

11、 Case of the Existence of Lone Pairs,LP/LP LP/VB VB/VB,Summary: Molecular Geometry Prediction,The geometry around an atom is described by the general formula: AXmEn Where X is a bonded atom, E is a lone pair and (m+n) is the number of objects (sometimes called the steric number, SN) around the centr

12、al atom A.,double or triply bonded atoms count the same as single bonded atoms in determining the SN (SN in CO2 is 2).,BF3 and NH3,N,H,H,H,SN(B) = 3SN(N) = 4 BF3 has 3 electron pairs = trigonal planar. NH3 has 4 electron pairs around the central N, but the molecular structure is trigonal pyramidal.,

13、SN=4, so VSEPR predicts a tetrahedral arrangement of 4 electron pairs. “normal” tetrahedral angle is 109.5 O. Experimental angle in CH4 = 109.5 O (no lone pairs).,Methane, CH4,Ammonia, NH3,SN=4, so VSEPR again predicts a tetrahedral arrangement of 4 electron pairs. “normal” tetrahedral angle is 109.

14、5 O. Experimental angle in NH3 = 107 O (one lone pair).,Water, H2O,SN=4, so VSEPR predicts a tetrahedral arrangement of 4 electron pairs. “normal” tetrahedral angle is 109.5 O. Experimental angle in H2O = 104.5 (2 lone pairs).,VSEPR notes,MoleculeSN# lone pairs PF5 5 0 SF4 5 1 ClF3 5 2 XeF2 5 3,PF5

15、- there are 2 axial and 3 equatorial sites. SF4 seesaw. ClF3 - the 2 lone pairs occupy equatorial positions to minimize the lone pair - lone pair interaction. XeF2 - similarly, 3 lone pairs in equatorial sites.,VSEPR notes,VSEPR notes,Double bonded species,The small gaseous molecule SO2, sulfur diox

16、ide, has S in the centre which uses 6 valence electrons SN = 3 ( 1lp, 2 bonding units) non-octet S Idealized shape = trigonal planar Actual shape = angular ( bent) Dipole moment = yes Please try SO32- and SO42-,S O O,HOMEWORK 11, 15, 16, 17,5.3 Valence Bond Orbitals,Non-Equivalent hybridization,x,y,z,HOH=104.5,H-O-H in xy plane LP-O-LP in yz plane,For the two hybrids pointing to hydrogen atoms, the hybridization style is the same.,a,b,sp4 hybridization,c,d,5.3 Valence Bond Orbitals,Non-Equivalent hybridization,5.3 Valence Bond Orbitals,Non-Equivale