1、Molecular Structure:Chemical Bonding and TheoryChapters 9&10Valence electrons are the outer shell electrons of an atom.The valence electrons are the electrons thatparticipate in chemical bonding.&1.How to distinguish covalent bond from ionic bond Li+FLi+F-1s22s11s22s22p51s21s22s22p6HeNeH+FH F1s11s22
2、s22p51s01s22s22p6NeLi+F-Ionic bond H FCovalent bandElectron transferredElectron sharede-riche-poord+d-HFElectronegativity is the ability of an atom to attract the electrons toward itself in a chemical bond.In 1932,Pauling defined the element electronegativity,on the basis F=4.0.Increasing difference
3、 in electronegativityClassification of bonds by difference in electronegativityDifferenceBond Type0Covalent 2Ionic0 and 2Polar Covalent F FLi+F-1.0 4.0 H F2.1 4.0Covalent Polar covalent ionic Share e-partially transfer e-transfer e-Classify the following bonds as ionic,polar covalent,or covalent:The
4、 bond in CsCl;the bond in H2S;andthe NN bond in H2NNH2.Cs 0.7Cl 3.03.0 0.7=2.3IonicH 2.1S 2.52.5 2.1=0.4Polar CovalentN 3.0N 3.03.0 3.0=0Covalent9.5Lattice energy(U)increases as Q increases and/or as r decreases.U Q+Q-rQ+is the charge on the cationQ-is the charge on the anionr is the distance betwee
5、n the ionsLattice energy(U)is the energy(kJ/mol)required to completely separate one mole of a solid ionic compound into gaseous ions.&2 Ionic Bond:Lattice Energy&Born-Haber CycleCompounds NaI NaBr NaCl NaF BaO SrO CaO MgO BeO r/pm 318 294 279 231 277 257 240 210 165U/kJmol-1 686 732 786 891 3041 320
6、4 3476 3916 -Tm.p/K 933 1013 1074 1261 2196 2703 2843 3073 2833Born-Haber Cycle for Determining Lattice EnergyDHoverall=DH1+DH2+DH3+DH4+DH5ooooooLattice energy(U)Comparison of Ionic and Covalent Compounds9.4covalent bond parametersa)Lengths of Covalent Bondsthe average distance between two nucleus.B
7、ond LengthsTriple bond Double Bond Single Bond&3 Covalent Bond:Molecular Geometry and Bond Theory Atomic radiiH 37 pmI 133 pmoverlapping(b)Bond energy:the enthalpy change required to break a particular bond in one mole of gaseous molecules.Cl2(g)Cl(g)+Cl(g)DH0=242.7 kJThe bond energy of unlike eleme
8、nts is the average bond energy measured in polyatomic moleculesH2O(g)H(g)+OH(g)DH0=502 kJOH(g)H(g)+O(g)DH0=427 kJO-H bond energy=5024274642kJFor a reaction,the enthalpy change can be estimated by bond energyDH0=total bond energy of reactants)total bond energy of products)(C)Bond angle:the angle betw
9、een two adjacent bonds.O3 ozone(b.p-111.3 oC)OO O116.5o148 pm210 kJStronger oxidant than O2148 pm,210 kJ468 kJused mainly for purification of drinking water,deodorization of air ad swage gases,and bleaching of oils and textiles.Environmentally friendly reagent Predict molecule geometry,based on the
10、electrostatic repulsions between the electron pairs(bonding and nonbonding).&4.VSEPR model(Valence shell electron pair repulsion)BeCl2ClClBeCentral atom Be He 2s2A:Total number of electron pairs(SN)=number of bonding pairs+number of lone pairsSN=2NH3CH4SN=4C He2s22p2 N He2s22p3 SN=4Tetrahedral(四面体四面
11、体)Trigonal pyramidal(三角锥体三角锥体)linearBond angle=107.3oGeometry of ABx molecules and ions in which A has no lone PairsSN SN SN SN SNSNSNSNSNSNSNSNSNDipole Moments and Polar Molecules10.2HFelectron richregionelectron poorregiondd-Dipole moment m=Q x rQ is the charge,r is the distance between charges1 D
12、=3.36 x 10-30 C m10.210.210.2Which of the following molecules have a dipole moment?H2O,CO2,SO2,and CH4OHHdipole momentpolar moleculeSOOCOOno dipole momentnonpolar moleculedipole momentpolar moleculeCHHHHno dipole momentnonpolar moleculeDoes CH2Cl2 have a dipole moment?10.210.2+-+&5 Valence Bond Theo
13、ry and Hybridization of Atomic OrbitalsH +H =H21s(e-)+1s(e-)=bond(2e-)Re=73 pm Bond energy=45.8 kJatomic orbital overlappingN 1s22s22p33 H 1s1If the bonds form from overlap of 3 2p orbitals on nitrogenwith the 1s orbital on each hydrogen atom,what would the molecular geometry of NH3 be?If use the3 2
14、p orbitalspredict 900Actual H-N-Hbond angle is107.30NH3CH4C He2s22p2H 1s1 sp3HHHHCBond angle 109.5 o4 equivalent sp3 hybrid oribitalsHybridization:mixing of two or more atomic orbitals to form a new set of hybrid orbitals.The hybrid orbitals have very different shape from original atomic orbitals.Th
15、e number of the hybrid orbitals is equal to the number of pure atomic orbitals used for the hybridization.The covalent bonds are then formed by overlapping the hybrid orbitals with atomic orbitals;or by overlapping the hybrid orbitals with other hybrid orbitalsspBeCl2Linear geometrysp2BF3TrigonalPla
16、narBond angle120 oN He2s22p33 H 1s1NH3sp3hybridizationsp3 hybrid orbitalssp3-hybridized O Atom in H2O107.3o 104.5o SF6S Ne3s23p4F He2s22p53s3p3dPromotion +sp3d2of e-hybridizationsp3d2 hybrid orbitalsEmpty 3d orbitalsOctahedron(八面体八面体)PBr5sp3dhybridizationTrigonalbipyramidal(三角双锥体三角双锥体)CH2CH2ethylene
17、C CHHHHPromotion of e-sp2 hybridizationCHCHacethyleneC CHHPromotion of e-sp hybridization Bond is more active bond Benzene C6H6Carbonate CO32-C+2O+O2-OO2-6664Delocalized systemthe bonds are formed by molecular orbitals,which results from the interaction of atomic orbitals in the molecule.OONo unpair
18、ed e-Experiments showing that O2 is paramagnetic&5 Molecular Orbital Theory(MO)According to valence band theory,liquid oxygen is diamagnetic.Paramagneticunpaired electrons2pDiamagneticall electrons paired2p7.8Application of Schrdinger to Hydrogen Molecule A B12rA2rB1rA1rB2Rr12ErrrrrRBABA-)111111()(2
19、11222112221in an atomic unitThe method used for the solution is called LCAO(Linear combination of atomic orbitals)2211ccMO(I atomic orbital)+_Bonding MOAnti-bonding MOHHH2Li 1s2 2s1Li2 molecule0*2222*121)()()()(ssssBond order1)24(21-e number in bonding MOe number inanti-bonding MObond order10The higher the bond order,the stronger the bond.HOMO(highest occupied MO)LUMO(lowest un-occupied MO)Two possible interaction between two p orbitals:(1)Head to Head(2)Shoulder to ShoulderLUMO HOMO Exercises:9.73 9.120 10.10 10.24 10.37 10.88
