分子結(jié)構(gòu)化學(xué)原理

1、Chapter 6Molecular structure and Bonding物質(zhì)結(jié)構(gòu)（2）1. How the shapes of simple molecules can be described and predicted 2. Examin why molecules have the shapes they do and look more closely at how atoms use their electrons to form bonds.2022/7/81空間構(gòu)型分子原子化學(xué)鍵共價鍵離子鍵金屬鍵雜化軌道理論VBMOVSEPR鍵的極性物質(zhì)分子間作用力分子的極性Atomic

2、 orbitalElectronFunction偶極矩2022/7/821927年， Heitler W 和 London F., 揭示共價鍵本質(zhì) Pauling L 和 Slater JC ，現(xiàn)代價鍵理論1932年， Muiliken RS 和 Hund F ，分子軌道理論1931年，Pauling L ，雜化軌道理論1954年，Pauling L ，Nobel prize1966年， Muiliken RS, Nobel prize1916年， Kossel, 離子鍵1923年， Lewis, 共價鍵原子的價電子理論2022/7/836.1 Molecular Geometries - L

3、ewis Structures: The octet rule - The VSEPR model6.2 Covalent Bonding - Valance-bond theory - Hybrid Orbitals6.3 Molecular orbital theory - The Hydrogen molecules - Molecular orbitals for second-period diatomic molecules2022/7/84Lewis structures give atomic connectivity6.1 Molecular GeometriesHNHHbo

4、nding pair of e-lone pair of e-Octet Rule: Each atom shares electrons with neighboring atoms to achieve a total of 8 valence electrons.- Lewis Structures :The octet rule2022/7/85Molecular ShapesBond Parameter鍵長(bond length) 鍵角(bond angle) 分子的空間構(gòu)型2022/7/86ABn2022/7/87Valence Shell Electron Pair Repul

5、sion (VSEPR) theorybonding pairs of electrons (bp)lone pairs ( lp )lplplpbpbpbpThe electrons adopt an arrangement in space to minimize e-e- repulsion.斥力大小的順序：bonding pair of e-lone pair of e- The VSEPR modelSigma 鍵電子對2022/7/882022/7/89Predicting Molecular Geometries確定中心原子價層e總數(shù)及e對數(shù)中心原子的價e對按斥力大小順序，空間排

6、布應(yīng)取斥力最小的排布方式，e對盡可能遠(yuǎn)離且呈對稱結(jié)構(gòu)drawcountarrange中心原子配位原子族序數(shù)鍵合電子孤對電子主族元素2022/7/8102022/7/8112022/7/8122022/7/813ClF3分子構(gòu)型：T字型電子構(gòu)型與分子構(gòu)型不一致電子數(shù)為5時，孤對總是盡先處于三角雙錐的腰部位置location of the lone pairs2022/7/814The VSEPR ModelMolecules with Expanded Valence Shells2022/7/815判斷 BF3及NF3的價層電子對構(gòu)型及分子構(gòu)型。（Give the electron-pair

7、geometry and the molecular geometry of BF3 and NF3.）BF3NF32022/7/816-Lewis structures and VSEPR do not explain why a bond forms.SHHOHH2022/7/8176.2 Covalent Bonding 價鍵理論雜化軌道理論Valence bond theory (VB)Hybrid orbital theory2022/7/818Walther Kossel1916離子鍵（ionic bond）2022/7/8191923年， Lewis GN, Irving Lan

8、gmuir, 經(jīng)典的共價鍵理論，HNHHLess than octet - ex: BF3More than octet - ex: PCl5共價健(Covalent bond)2022/7/820attractive forcesrepulsive forcesBond Length1927年， Heitler W 和 London F., 揭示共價鍵本質(zhì)2022/7/821Covalent Bonding and Orbital Overlap2022/7/822共價鍵的本質(zhì)本質(zhì)上是電性的。但它不同于一般的靜電作用，它是兩原子核共同對核間電子云密集區(qū)的吸引。2022/7/823將H2的研究

9、結(jié)果推廣至其它雙原子分子和多原子分子價鍵理論自旋相反的單電子配對自旋相反的單電子配對后，不能再和其它原子中的單電子配對，形成共價鍵的數(shù)目與該原子中單電子數(shù)目相同。飽和性共價鍵的形成盡可能沿著原子軌道最大重疊的方向進(jìn)行，即原子軌道最大重疊原理。方向性2022/7/824共價鍵類型鍵鍵s-ss-pxpx-px鍵軸（internuclear axis）xx軌道的重疊部分沿鍵軸呈圓柱形對稱分布 py-pypz-pz軌道的重疊部分垂直于鍵軸并呈鏡面反對稱分布 2022/7/825double bondstriple bondsMultiple Bonds共價鍵類型配位?。–oordination cov

10、alent bond）2022/7/826鍵參數(shù) (Bond Parameters)鍵能(bond energy) 鍵長(bond length) 鍵角(bond angle) 鍵的極性(Polarity of bond)分子的空間構(gòu)型電負(fù)性極性共價鍵(Polar covalent bond)非極性共價鍵(nonpolar covalent bond)2022/7/827e- riche- poorindicates a bond dipole2022/7/828Bond Type and DENEqual sharing of e- pairUnequal sharing of e- pai

11、r(Nearly) complete e- transfer2022/7/829分子的極性(Polarity of molecules)the charge distribution in a molecule雙原子分子的極性（The polarity diatomic molecule）Polar Molecule化學(xué)鍵的極性多原子分子的極性(The polarity of Polyatomic molecules)化學(xué)鍵的極性分子的空間構(gòu)型2022/7/8302022/7/831偶極矩() (dipole moment):The degree of polarityA quantitati

12、ve measure of the degree of charge separation in a molecule.2022/7/832Relating Dipole Moment and Molecular GeometryEach of the following molecules has a nonzero dipole moment. Select the molecular geometry that is consistent with this information. Explain your reasoning.SO2 linear, bentPH3 trigonal

13、planar, trigonal pyramidal2022/7/833Permanent dipole momentInduced dipole moment分子的極化(Molecular polarization)2022/7/834Problem:1954年，Pauling L ，Nobel prize1931年，Pauling L ，雜化軌道理論2022/7/835雜化軌道理論 (Hybrid orbital theory)General principles of Hybrid orbital theory Types of Hybrid orbitals Apply VSEPR T

14、heory and Determine Hybridization2022/7/836General principles of Hybrid orbital theory 鍵s-ss-pxpx-pxSP3 - s2022/7/837-成鍵過程中，同一原子中的幾個能量相近的原子軌道重新 組合成數(shù)目相等、能量相同、方向一定的新的原子軌道。-雜化軌道比原來的原子軌道的成鍵能力強(qiáng)。-雜化軌道具有確定的方向，軌道之間在空間上采取最大角度分布。Valence Bond Theory - atoms form bonds by overlapping atomic and/or hybrid orbita

15、ls2022/7/838SP3 雜化2022/7/839SP3 雜化2022/7/840等性雜化軌道(Equivalent hybrid orbital)不等性雜化軌道( Unequivalent hybrid orbital)2022/7/841 sp HybridizationVSEPR TheoryBe: 1s22s2Be: 1s22s12p1hybridization2022/7/842sp雜化鍵s-ss-pxpx-pxSP3 - pSP - p2022/7/843BF3 - trigonal planar sp2 HybridizationVSEPR Theory2022/7/844

16、sp2雜化鍵s-ss-pxpx-pxSP3 - pSP - pSP2 - p2022/7/845 sp3d HybridizationVSEPR Theorytrigonal bipyramidal2022/7/846For PF5, we need 5 hybrid orbitals, so 5 atomic orbitals are required as follows: (s + p + p + p + d) = sp3d2022/7/847Lewis StructureElectron Pair GeometryMolecular Geometry sp3d2 Hybridizati

17、onVSEPR Theoryoctahedral2022/7/848For SF6, we need 6 hybrid orbitals, so 6 atomic orbitals are required as follows: (s + p + p + p + d + d) = sp3d2Six sp3d2 hybridized orbitals for S-F bonds3 unhybridized d-orbitalsIsolated S atom2022/7/849Hybrid Orbitals and VSEPRWrite a Lewis structure (/Determine

18、 LP )Use VSEPR to predict electron geometry.Select the appropriate hybridization.Limitations:2022/7/850指出BF3 及NF3中心原子的雜化軌道，.(Indicate the hybrid orbital set used in BF3 and NF3.) BF3NF32022/7/8512022/7/852物質(zhì)的磁性與不成對電子數(shù)Background單電子2022/7/853 DiamagneticParamagneticall electrons are pairedBackground-M

19、agnetism and unpaired electronDiamagnetism(抗磁性)-Paramagnetism(順磁性)-unpaired electron2022/7/854VSEPR Theory - electron pair repulsions influence molecular shapeValence Bond Theory - atoms form bonds by overlapping atomic and/or hybrid orbitalsApplied to O2O = O Or H2+Problem:2022/7/8556.3 Molecular o

20、rbital theory1932年， Mulliken RS 和 Hund F ，分子軌道理論1966年， Muillken RS, Nobel prizeGeneral principles of Molecular orbital theory Types of molecular orbitals Molecular orbitals for second-period diatomic molecules 2022/7/856 3. 幾個原子軌道可組合成幾個分子軌道，其中一半為成鍵分子軌道（bonding molecular orbital）；另一半為反鍵分子軌道（antibondi

21、ng molecular orbital）。 1. 原子在形成分子時，分子中的電子在整個分子空間范圍內(nèi)運(yùn)動2. 在分子中電子的空間運(yùn)動狀態(tài)可用相應(yīng)的分子軌道波函數(shù)來描述。 General principles of Molecular orbital theory 2022/7/8572022/7/858軌道組合原則對稱性匹配(Symmetric matching)能量必須相近(Close energy level)最大重疊(Maximum overlap of atomic orbital)? Pz和py的對稱性匹配嗎？2022/7/8594. 填充分子軌道時服從電子填充原子軌道的三原則 5

22、 . 鍵級(Bond Order)Bond Order = No. e- in bonding MOs - No. e- in antibonding MOs 2Bond order determines molecular stability2022/7/860Types of molecular orbitals 成鍵軌道中，兩原子之間的電子云密度增加；反鍵軌道中，兩原子之間的電子云密度降低。Combining s orbitals2022/7/861Combining p orbitals2022/7/8622022/7/863O2, F2N22022/7/864Example: H2+

23、 ,H2 ,He2 and He2+ BO = (1-0)/2 = H2+BO = (2-0)/2 = 1 H2BO = (2-1)/2 = He2+BO = (2-2)/2 = 0 He2BO = (e-bond - e-antibond )/2 2022/7/8652022/7/866NO+N2CO等電子體(isoelectronic)MO Diagrams of Heteronuclear DiatomicsCO1.128CO+1.1152022/7/867Illustration of molecular orbitalO2 (s1s)2(s*1s)2 (s2s)2(s*2s)2 (s

24、2px)2 (p2py)2 (p2pz)2(p*2py)1 (p*2pz)1 or O2 KK (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)2(p*2py)1 (p*2pz)1N2 (s1s)2(s*1s)2 (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)2 or N2 KK (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)22022/7/868Molecular orbital theoryValence bond theoryAtomic orbitalOverlapCombination (LCAO)Elect

25、ronlocalizeddelocalizedFunctionGound stateExcited state2022/7/869自由基 (Free radical) HO2-OH KK (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)2(p*2py)2 (p*2pz)1Superoxide anion radical3O2 KK (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)2(p*2py)1 (p*2pz)11O2 KK (s2s)2(s*2s)2 (s2px)2 (p2py)2 (p2pz)2(p*2py)2 (p*2pz)02022/7/870Reactive oxygen species (ROS) rather than