武汉大学无机化学课件09

1、Chapter 9Covalent Bonding:OrbitalsSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved2Draw the Lewis structure for methane, CH4. What is the shape of a methane molecule? tetrahedral What are the bond angles? 109.5oCHHHHSection 9.1Hybridization and

2、 the Localized Electron ModelCopyright Cengage Learning. All rights reserved3What is the valence electron configuration of a carbon atom? s2p2Why cant the bonding orbitals for methane be formed by an overlap of atomic orbitals?Section 9.1Hybridization and the Localized Electron ModelCopyright Cengag

3、e Learning. All rights reserved4Bonding in Methane Assume that the carbon atom has four equivalent atomic orbitals, arranged tetrahedrally.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved5Hybridization Mixing of the native atomic orbitals to fo

4、rm special orbitals for bonding.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved6sp3 Hybridization Combination of one s and three p orbitals. Whenever a set of equivalent tetrahedral atomic orbitals is required by an atom, the localized electro

5、n model assumes that the atom adopts a set of sp3 orbitals; the atom becomes sp3 hybridized. The four orbitals are identical in shape.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved7An Energy-Level Diagram Showing the Formation of Four sp3 Orb

6、italsSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved8The Formation of sp3 Hybrid OrbitalsSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved9Tetrahedral Set of Four sp3 OrbitalsSection 9.1Hy

7、bridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved10Draw 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 angles around the carbon atoms? 120oCHCHHHSectio

8、n 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved11Why cant sp3 hybridization account for the ethylene molecule?Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved12sp2 Hybridization Combination of

9、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 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved13Sigma () Bond Electron pair i

10、s shared in an area centered on a line running between the atoms.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved14Pi () Bond Forms double and triple bonds by sharing electron pair(s) in the space above and below the bond. Uses the unhybridized

11、 p orbitals.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved15An Orbital Energy-Level Diagram for sp2 HybridizationSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved16The Hybridization of th

12、e s, px, and py Atomic OrbitalsSection 9.1Hybridization and the Localized Electron ModelFormation of C=C Double Bond in EthyleneCopyright Cengage Learning. All rights reserved17Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved18Draw the Lewis st

13、ructure for CO2. What is the shape of a carbon dioxide molecule? linear What are the bond angles? 180oCOOSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved19sp Hybridization Combination of one s and one p orbital. Gives a linear arrangement of at

14、omic orbitals. Two p orbitals are not used. Needed to form the bonds.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved20The Orbital Energy-Level Diagram for the Formation of sp Hybrid Orbitals on CarbonSection 9.1Hybridization and the Localized

15、Electron ModelCopyright Cengage Learning. All rights reserved21When One s Orbital and One p Orbital are Hybridized, a Set of Two sp Orbitals Oriented at 180 Degrees ResultsSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved22The Orbitals for CO2Se

16、ction 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved23Draw the Lewis structure for PCl5. What is the shape of a phosphorus pentachloride molecule? trigonal bipyramidal What are the bond angles? 90o and 120oPClClClClClSection 9.1Hybridization and the

17、Localized Electron ModelCopyright Cengage Learning. All rights reserved24dsp3 Hybridization Combination of one d, one s, and three p orbitals. Gives a trigonal bipyramidal arrangement of five equivalent hybrid orbitals.Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learni

18、ng. All rights reserved25The Orbitals Used to Form the Bonds in PCl5Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved26Draw the Lewis structure for XeF4. What is the shape of a xenon tetrafluoride molecule? octahedral What are the bond angles? 9

19、0o and 180oXeFFFFSection 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved27d2sp3 Hybridization Combination of two d, one s, and three p orbitals. Gives an octahedral arrangement of six equivalent hybrid orbitals.Section 9.1Hybridization and the Localiz

20、ed Electron ModelCopyright Cengage Learning. All rights reserved28How is the Xenon Atom in XeF4 Hybridized?Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved29Draw the Lewis structure for HCN.Which hybrid orbitals are used?Draw HCN:Showing all bo

21、nds between atoms.Labeling each bond as or .Section 9.1Hybridization and the Localized Electron ModelDetermine the bond angle and expected hybridization of the central atom for each of the following molecules:NH3SO2KrF2CO2ICl5NH3 109.5o, sp3SO2 120o, sp2KrF2 90o, 120o, dsp3CO2 180o, spICl5 90o, 180o

22、, d2sp3Section 9.1Hybridization and the Localized Electron ModelCopyright Cengage Learning. All rights reserved31Using the Localized Electron Model Draw the Lewis structure(s). Determine the arrangement of electron pairs using the VSEPR model. Specify the hybrid orbitals needed to accommodate the el

23、ectron pairs.Section 9.2The Molecular Orbital Model Regards a molecule as a collection of nuclei and electrons, where the electrons are assumed to 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 tha

24、n always located between a given pair of atoms.Copyright Cengage Learning. All rights reserved32Section 9.2The Molecular Orbital Model The electron probability of both molecular orbitals is centered along the line passing through the two nuclei. Sigma () molecular orbitals (MOs) In the molecule only

25、 the molecular orbitals are available for occupation by electrons.Copyright Cengage Learning. All rights reserved33Section 9.2The Molecular Orbital Model Molecular Orbital Theory (MO) Atomic orbitals combine to form new molecular orbitals which are spread out over the entire molecule. Electrons are

26、in orbitals that belong to the molecule as a whole. Molecular orbitals (wave functions) result from adding and/or subtracting atomic orbitals (wave functions). Section 9.2The Molecular Orbital ModelH2+: The Simplest MoleculeRerereRrrVBABA020202444);,(Electron-nuclearattractioninternuclearrepulsionBo

27、rn-Oppenheimer approximationset of wavefunctions, y(x,y,z;R), describing the quantum state of the electron called molecular orbitalsSection 9.2The Molecular Orbital ModelLinear Combinations of Atomic Orbitals LCAOsBBsAAMOccBA11,),(y),(),(ABBAMOMO22yy),(),(ABBAMOMOyywhich impliesbecause cA=cB or cA=-

28、cB, there are only two possible molecular orbitals. Orbitals are conserved.Section 9.2The Molecular Orbital ModelsBsA1121,ysBsA1121,ylower energyhigher energys (sigma) Section 9.2The Molecular Orbital ModelEnergy as a Function of Internuclear Separationhigher energySection 9.2The Molecular Orbital M

29、odelCombination of Hydrogen 1s Atomic Orbitals to form MOsCopyright Cengage Learning. All rights reserved39Section 9.2The 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 Ant

30、ibonding molecular orbital higher in energyCopyright Cengage Learning. All rights reserved40Section 9.2The Molecular Orbital ModelMO Energy-Level Diagram for the H2 MoleculeCopyright Cengage Learning. All rights reserved41Section 9.2The Molecular Orbital Model The molecular orbital model produces el

31、ectron distributions and energies that agree with our basic ideas of 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 reserved42Section 9.2The Molecular Orbital Mo

32、del Molecular electron configurations can be written in much the 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 reserved43Section 9.2The Molecular Orbital ModelSi

33、gma Bonding and Antibonding OrbitalsCopyright Cengage Learning. All rights reserved44Section 9.2The Molecular Orbital ModelBond Order Larger bond order means greater bond strength.Copyright Cengage Learning. All rights reserved45# of bonding e # of antibonding eBond order = 2Section 9.2The Molecular

34、 Orbital ModelExample: H22 0Bond order = = 12Section 9.2The Molecular Orbital ModelExample: H2Copyright Cengage Learning. All rights reserved472 11Bond order = = 22Section 9.3Bonding in Homonuclear Diatomic MoleculesHomonuclear Diatomic Molecules Composed of 2 identical atoms. Only the valence orbit

35、als of the atoms contribute significantly to the molecular orbitals of a particular molecule.Copyright Cengage Learning. All rights reserved48Section 9.3Bonding in Homonuclear Diatomic MoleculesPi Bonding and Antibonding OrbitalsCopyright Cengage Learning. All rights reserved49Section 9.3Bonding in

36、Homonuclear Diatomic MoleculesThe number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined.The more stable the bonding MO, the less stable the corresponding antibonding MO.The filling of MOs proceeds from low to high energies.Each MO can accommodate up to t

37、wo electrons.Use Hunds rule when adding electrons to MOs of the same energy.1. The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms.Molecular Orbital (MO) ConfigurationsSection 9.3Bonding in Homonuclear Diatomic MoleculesParamagnetism Paramagnetism substan

38、ce is attracted 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 reserved51Section 9.3Bonding in Homonuclear Diatomic MoleculesApparatus Used to Measure the Param

39、agnetism of a SampleCopyright Cengage Learning. All rights reserved52Section 9.3Bonding in Homonuclear Diatomic MoleculesMolecular Orbital Summary of Second Row Diatomic MoleculesCopyright Cengage Learning. All rights reserved53Section 9.4Bonding in Heteronuclear Diatomic MoleculesHeteronuclear Diat

40、omic Molecules Composed of 2 different atoms.Copyright Cengage Learning. All rights reserved54Section 9.4Bonding in Heteronuclear Diatomic MoleculesHeteronuclear Diatomic Molecule: HF The 2p orbital of fluorine is at a lower energy than the 1s orbital of hydrogen because fluorine binds its valence e

41、lectrons 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 reserved55Section 9.4Bonding in Heteronuclear Diatomic MoleculesOrbital Ene

42、rgy-Level Diagram for the HF MoleculeCopyright Cengage Learning. All rights reserved56Section 9.4Bonding in Heteronuclear Diatomic MoleculesHeteronuclear Diatomic Molecule: HF The diagram predicts that the HF molecule should be stable because both electrons are lowered in energy relative to their en

43、ergy in the free hydrogen and fluorine atoms, which is the driving force for bond formation.Copyright Cengage Learning. All rights reserved57Section 9.4Bonding in Heteronuclear Diatomic MoleculesThe Electron Probability Distribution in the Bonding Molecular Orbital of the HF MoleculeCopyright Cengag

44、e Learning. All rights reserved58Section 9.4Bonding in Heteronuclear Diatomic MoleculesHeteronuclear 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 equally. This causes the flu

45、orine 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 reserved59Section 9.4Bonding in Heteronuclear Diatomic MoleculesCOOCMO Theory for Heteronuclear Diatomics MO

46、s 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 YMOYX makes a greater contribution

47、to the Y*MOEnergyThe MO diagram for NOMO of NO2sAO of N2ps*sss2sAO of O2ppsp*ps*sNO00possible Lewis structuresAO(2)AO(1)Molecular Orbital TheoryAO(2)AO(1)AO(2)AO(1)AO(2)AO(1)Most covalentPolar CovalentIonicRemember that the closer to AOs of appropriate symmetry are in energy, the more they interact

48、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 the bond increases). If the difference in energy of the orbitals

49、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 Theory and Polyatomic Molecules MO diagrams are complicated for polyato

50、mics. 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 MOsConsider 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 make LGOs.D