武汉大学无机化学课件09

1、Chapter 9 Covalent Bonding: Orbitals Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved2 Draw the Lewis structure for methane, CH4. What is the shape of a methane molecule? tetrahedral What are the bond angles? 109.5o C H HH H Section 9.1 Hybri

2、dization and the Localized Electron Model Copyright Cengage Learning. All rights reserved3 What is the valence electron configuration of a carbon atom? s2p2 Why cant the bonding orbitals for methane be formed by an overlap of atomic orbitals? Section 9.1 Hybridization and the Localized Electron Mode

3、l Copyright Cengage Learning. All rights reserved4 Bonding in Methane Assume that the carbon atom has four equivalent atomic orbitals, arranged tetrahedrally. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved5 Hybridization Mixing of the nativ

4、e atomic orbitals to form special orbitals for bonding. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved6 sp3 Hybridization Combination of one s and three p orbitals. Whenever a set of equivalent tetrahedral atomic orbitals is required by an

5、atom, the localized electron model assumes that the atom adopts a set of sp3 orbitals; the atom becomes sp3 hybridized. The four orbitals are identical in shape. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved7 An Energy-Level Diagram Showin

6、g the Formation of Four sp3 Orbitals Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved8 The Formation of sp3 Hybrid Orbitals Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved9 Tetrahedra

7、l Set of Four sp3 Orbitals Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved10 Draw the Lewis structure for C2H4 (ethylene)? What is the shape of an ethylene molecule? trigonal planar around each carbon atom What are the approximate bond angle

8、s around the carbon atoms? 120o C H C H HH Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved11 Why cant sp3 hybridization account for the ethylene molecule? Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning.

9、 All rights reserved12 sp2 Hybridization Combination of one s and two p orbitals. Gives a trigonal planar arrangement of atomic orbitals. One p orbital is not used. Oriented perpendicular to the plane of the sp2 orbitals. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage L

10、earning. All rights reserved13 Sigma () Bond Electron pair is shared in an area centered on a line running between the atoms. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved14 Pi () Bond Forms double and triple bonds by sharing electron pair

11、(s) in the space above and below the bond. Uses the unhybridized p orbitals. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved15 An Orbital Energy-Level Diagram for sp2 Hybridization Section 9.1 Hybridization and the Localized Electron Model C

12、opyright Cengage Learning. All rights reserved16 The Hybridization of the s, px, and py Atomic Orbitals Section 9.1 Hybridization and the Localized Electron Model Formation of C=C Double Bond in Ethylene Copyright Cengage Learning. All rights reserved17 Section 9.1 Hybridization and the Localized El

13、ectron Model Copyright Cengage Learning. All rights reserved18 Draw the Lewis structure for CO2. What is the shape of a carbon dioxide molecule? linear What are the bond angles? 180o COO Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved19 sp H

14、ybridization Combination of one s and one p orbital. Gives a linear arrangement of atomic orbitals. Two p orbitals are not used. Needed to form the bonds. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved20 The Orbital Energy-Level Diagram for

15、 the Formation of sp Hybrid Orbitals on Carbon Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved21 When One s Orbital and One p Orbital are Hybridized, a Set of Two sp Orbitals Oriented at 180 Degrees Results Section 9.1 Hybridization and the

16、Localized Electron Model Copyright Cengage Learning. All rights reserved22 The Orbitals for CO2 Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved23 Draw the Lewis structure for PCl5. What is the shape of a phosphorus pentachloride molecule? tr

17、igonal bipyramidal What are the bond angles? 90o and 120o P Cl Cl Cl Cl Cl Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved24 dsp3 Hybridization Combination of one d, one s, and three p orbitals. Gives a trigonal bipyramidal arrangement of fi

18、ve equivalent hybrid orbitals. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved25 The Orbitals Used to Form the Bonds in PCl5 Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved26 Draw th

19、e Lewis structure for XeF4. What is the shape of a xenon tetrafluoride molecule? octahedral What are the bond angles? 90o and 180o Xe F FF F Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved27 d2sp3 Hybridization Combination of two d, one s, a

20、nd three p orbitals. Gives an octahedral arrangement of six equivalent hybrid orbitals. Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved28 How is the Xenon Atom in XeF4 Hybridized? Section 9.1 Hybridization and the Localized Electron Model Co

21、pyright Cengage Learning. All rights reserved29 Draw the Lewis structure for HCN. Which hybrid orbitals are used? Draw HCN: Showing all bonds between atoms. Labeling each bond as or . Section 9.1 Hybridization and the Localized Electron Model Determine the bond angle and expected hybridization of th

22、e central atom for each of the following molecules: NH3SO2KrF2 CO2ICl5 NH3 109.5o, sp3 SO2 120o, sp2 KrF2 90o, 120o, dsp3 CO2 180o, sp ICl5 90o, 180o, d2sp3 Section 9.1 Hybridization and the Localized Electron Model Copyright Cengage Learning. All rights reserved31 Using the Localized Electron Model

23、 Draw the Lewis structure(s). Determine the arrangement of electron pairs using the VSEPR model. Specify the hybrid orbitals needed to accommodate the electron pairs. Section 9.2 The Molecular Orbital Model Regards a molecule as a collection of nuclei and electrons, where the electrons are assumed t

24、o occupy orbitals much as they do in atoms, but having the orbitals extend over the entire molecule. The electrons are assumed to be delocalized rather than always located between a given pair of atoms. Copyright Cengage Learning. All rights reserved32 Section 9.2 The Molecular Orbital Model The ele

25、ctron probability of both molecular orbitals is centered along the line passing through the two nuclei. Sigma () molecular orbitals (MOs) In the molecule only the molecular orbitals are available for occupation by electrons. Copyright Cengage Learning. All rights reserved33 Section 9.2 The Molecular

26、 Orbital Model Molecular Orbital Theory (MO) Atomic orbitals combine to form new molecular orbitals which are spread out over the entire molecule. Electrons are in orbitals that belong to the molecule as a whole. Molecular orbitals (wave functions) result from adding and/or subtracting atomic orbita

27、ls (wave functions). Section 9.2 The Molecular Orbital Model H2+: The Simplest Molecule R e r e r e RrrV BA BA 0 2 0 2 0 2 444 );,( Electron-nuclear attraction internuclear repulsion Born-Oppenheimer approximation set of wavefunctions, y(x,y,z;R), describing the quantum state of the electron called

28、molecular orbitals Section 9.2 The Molecular Orbital Model Linear Combinations of Atomic Orbitals LCAO sBBsAAMO ccBA 11, ),(y ),(),(ABBAMOMO 22 yy ),(),(ABBA MOMO yy which implies because cA=cB or cA=-cB, there are only two possible molecular orbitals. Orbitals are conserved. Section 9.2 The Molecul

29、ar Orbital Model sBsA11 2 1 , y sBsA11 2 1 , y lower energy higher energy s (sigma) Section 9.2 The Molecular Orbital Model Energy as a Function of Internuclear Separation higher energy Section 9.2 The Molecular Orbital Model Combination of Hydrogen 1s Atomic Orbitals to form MOs Copyright Cengage L

30、earning. All rights reserved39 Section 9.2 The Molecular Orbital Model MO1 is lower in energy than the s orbitals of free atoms, while MO2 is higher in energy than the s orbitals. Bonding molecular orbital lower in energy Antibonding molecular orbital higher in energy Copyright Cengage Learning. All

31、 rights reserved40 Section 9.2 The Molecular Orbital Model MO Energy-Level Diagram for the H2 Molecule Copyright Cengage Learning. All rights reserved41 Section 9.2 The Molecular Orbital Model The molecular orbital model produces electron distributions and energies that agree with our basic ideas of

32、 bonding. The labels on molecular orbitals indicate their symmetry (shape), the parent atomic orbitals, and whether they are bonding or antibonding. Copyright Cengage Learning. All rights reserved42 Section 9.2 The Molecular Orbital Model Molecular electron configurations can be written in much the

33、same way as atomic electron configurations. Each molecular orbital can hold 2 electrons with opposite spins. The number of orbitals are conserved. Copyright Cengage Learning. All rights reserved43 Section 9.2 The Molecular Orbital Model Sigma Bonding and Antibonding Orbitals Copyright Cengage Learni

34、ng. All rights reserved44 Section 9.2 The Molecular Orbital Model Bond Order Larger bond order means greater bond strength. Copyright Cengage Learning. All rights reserved45 # of bonding e # of antibonding e Bond order = 2 Section 9.2 The Molecular Orbital Model Example: H2 2 0 Bond order = = 1 2 Se

35、ction 9.2 The Molecular Orbital Model Example: H2 Copyright Cengage Learning. All rights reserved47 2 11 Bond order = = 22 Section 9.3 Bonding in Homonuclear Diatomic Molecules Homonuclear Diatomic Molecules Composed of 2 identical atoms. Only the valence orbitals of the atoms contribute significant

36、ly to the molecular orbitals of a particular molecule. Copyright Cengage Learning. All rights reserved48 Section 9.3 Bonding in Homonuclear Diatomic Molecules Pi Bonding and Antibonding Orbitals Copyright Cengage Learning. All rights reserved49 Section 9.3 Bonding in Homonuclear Diatomic Molecules 1

37、. The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined. 2. The more stable the bonding MO, the less stable the corresponding antibonding MO. 3. The filling of MOs proceeds from low to high energies. 4. Each MO can accommodate up to two electrons. 5.

38、 Use Hunds rule when adding electrons to MOs of the same energy. 6. The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms. Molecular Orbital (MO) Configurations Section 9.3 Bonding in Homonuclear Diatomic Molecules Paramagnetism Paramagnetism substance is a

39、ttracted into the inducing magnetic field. Unpaired electrons (O2) Diamagnetism substance is repelled from the inducing magnetic field. Paired electrons (N2) Copyright Cengage Learning. All rights reserved51 Section 9.3 Bonding in Homonuclear Diatomic Molecules Apparatus Used to Measure the Paramagn

40、etism of a Sample Copyright Cengage Learning. All rights reserved52 Section 9.3 Bonding in Homonuclear Diatomic Molecules Molecular Orbital Summary of Second Row Diatomic Molecules Copyright Cengage Learning. All rights reserved53 Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear

41、 Diatomic Molecules Composed of 2 different atoms. Copyright Cengage Learning. All rights reserved54 Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF The 2p orbital of fluorine is at a lower energy than the 1s orbital of hydrogen because fluorine binds its

42、valence electrons more tightly. Electrons prefer to be closer to the fluorine atom. Thus the 2p electron on a free fluorine atom is at a lower energy than the 1s electron on a free hydrogen atom. Copyright Cengage Learning. All rights reserved55 Section 9.4 Bonding in Heteronuclear Diatomic Molecule

43、s Orbital Energy-Level Diagram for the HF Molecule Copyright Cengage Learning. All rights reserved56 Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF The diagram predicts that the HF molecule should be stable because both electrons are lowered in energy rel

44、ative to their energy in the free hydrogen and fluorine atoms, which is the driving force for bond formation. Copyright Cengage Learning. All rights reserved57 Section 9.4 Bonding in Heteronuclear Diatomic Molecules The Electron Probability Distribution in the Bonding Molecular Orbital of the HF Mol

45、ecule Copyright Cengage Learning. All rights reserved58 Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF The molecular orbital containing the bonding electron pair shows greater electron probability close to the fluorine. The electron pair is not shared equ

46、ally. This causes the fluorine atom to have a slight excess of negative charge and leaves the hydrogen atom partially positive. This is exactly the bond polarity observed for HF. Copyright Cengage Learning. All rights reserved59 Section 9.4 Bonding in Heteronuclear Diatomic Molecules CO OC MO Theory

47、 for Heteronuclear Diatomics MOs will no longer contain equal contributions from each AO. AOs interact if symmetries are compatible. AOs interact if energies are close. No interaction will occur if energies are too far apart. A nonbonding orbital will form. YY makes a greater contribution to the YMO

48、 YX makes a greater contribution to the Y*MO Energy The MO diagram for NO MO of NO 2s AO of N 2p s* s s s 2s AO of O 2p p s p * p s* s NO 00 possible Lewis structures AO(2)AO(1) Molecular Orbital Theory AO(2) AO(1) AO(2) AO(1) AO(2) AO(1) Most covalentPolar CovalentIonic Remember that the closer to

49、AOs of appropriate symmetry are in energy, the more they interact with one another and the more stable the bonding MO that will be formed. This means that as the difference in electronegativity between two atoms increases, the stabilization provided by covalent bonding decreases (and the polarity of

50、 the bond increases). If the difference in energy of the orbitals is sufficiently large, then covalent bonding will not stabilize the interaction of the atoms. In that situation, the less electronegative atom will lose an electron to the more electronegative atom and two ions will be formed. MO Theo

51、ry and Polyatomic Molecules MO diagrams are complicated for polyatomics. For example, CO2 requires drawing a diagram with four sets of orbitals (3 AOs and 1 MO). To simplify the problem we use the ligand group orbital approach (LGO) Ligand Group Orbital (LGO) Approach to MOs Consider XH2, a linear molecule, oriented along the z-axis. Let X have 2s and 2p orbitals. The 1s orbitals on H have two possible phases. Take the two Hs as a group to m