化学原理Chemistry课件-post+5+Chemical+bonding

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+FHF1s1

2、1s22s22p51s01s22s22p6NeLi+ F-Ionic bondCovalent 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 di

3、fference in electronegativityClassification of bonds by difference in electronegativityDifferenceBond Type0Covalent 2Ionic0 and 2Polar CovalentLi+ F-1.0 4.02.1 4.0Covalent Polar covalent ionic Share e- partially transfer e- transfer e- Classify the following bonds as ionic, polar covalent, or covale

4、nt: The 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

5、the distance between 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 /kJm

6、ol-1 686 732 786 891 3041 3204 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 parametersLengths of Covalent Bondsth

7、e average distance between two nucleus.Bond 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

8、 (g)DH0 = 242.7 kJThe bond energy of unlike elements 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 =kJFor a reaction, the enthalpy change can be estimated by bond energyDH0 = total bond energy of reactants) tota

9、l bond energy of products)(C) Bond angle: the angle between 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.Environment

10、ally friendly reagent Predict molecule geometry, based on the 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

11、of lone pairsSN=2NH3CH4SN=4C He2s22p2 N He2s22p3 SN=4Tetrahedral (四面体)Trigonal pyramidal(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 poorregiond+d-Dipole

12、 moment m = Q x rQ is the charge,r is the distance between charges1 D = 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 momentnonpola

13、r moleculeDoes CH2Cl2 have a dipole moment?10.210.2+-+& 5 Valence Bond Theory 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 or

14、bital on each hydrogen atom, what would the molecular geometry of NH3 be?If use the3 2p 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

15、orbitals.The hybrid orbitals have very different shape from original atomic orbitals.The 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 overlapp

16、ing the hybrid orbitals with other hybrid orbitalsspBeCl2Linear geometrysp2BF3TrigonalPlanarBond angle120 oN He2s22p33 H 1s1NH3sp3hybridizationsp3 hybrid orbitalssp3-hybridized O Atom in H2O107.3o 104.5o SF6S Ne3s23p4F He2s22p53s3p3dPromotion + sp3d2of e- hybridizationsp3d2 hybrid orbitalsEmpty 3d o

17、rbitalsOctahedron(八面体)PBr5sp3dhybridizationTrigonalbipyramidal(三角双锥体)CH2CH2ethylenePromotion of e-sp2 hybridizationCHCHacethylenePromotion of e-sp hybridization Bond is more active bond BenzeneC6H6Carbonate CO32-C+2O + O2-OO2-Delocalized systemthe bonds are formed by molecular orbitals, which result

18、s from the interaction of atomic orbitals in the molecule.OONo unpaired 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 B12rA2rB1rA1rB2Rr12in an atomic unitThe method used for the solution is called LCAO(Linear combination of atomic orbitals) MO(I atomic orbital)+_Bonding MOAnti-bonding MOHHH2Li 1s2 2s1Li2 moleculeBond ordere number in