chemicalBonding化学键解析课件.ppt

1、Ionic BondingResonance StructuresVSEPRBasic Shapes3-D NotationHybridization(Lab)Molecular GeometriesOctet RulePolar MoleculesLewis StructuresCovalent BondingTypes of BondsChemical Bonding Chemical bond:attractive force holding two or more atoms together.Covalent bond results from sharing electrons b

2、etween the atoms.Usually found between nonmetals.Ionic bond results from the transfer of electrons from a metal to a nonmetal.Metallic bond:attractive force holding pure metals together.Chemical BondsBond Type Single Double Triple#of es 2 4 6Notation =Bond order 1 2 3Bond strengthIncreases from Sing

3、le to TripleBond lengthDecreases from Single to TripleLewis SymbolsThe Octet Rule All noble gases except He has an s2p6 configuration.Octet rule:atoms tend to gain,lose,or share electrons until they are surrounded by 8 valence electrons(4 electron pairs).Caution:there are many exceptions to the octe

4、t rule.Electronegativity Electronegativity:The ability of one atoms in a molecule to attract electrons to itself.Pauling set electronegativities on a scale from 0.7(Cs)to 4.0(F).Electronegativity increases across a period and down a group.ElectronegativityFigure 8.7:Electronegativity and Bond Polari

5、ty There is no sharp distinction between bonding types.The positive end(or pole)in a polar bond is represented+and the negative pole-.HyperChemFollow Step by Step Method(See Ng Web-site)1.Total all valence electrons.Consider Charge2.Write symbols for the atoms and guess skeleton structure define a c

6、entral atom.3.Place a pair of electrons in each bond.4.Complete octets of surrounding atoms.H=2 only 5.Place leftover electrons in pairs on the central atom.6.If there are not enough electrons to give the central atom an octet,look for multiple bonds by transferring electrons until each atom has eig

7、ht electrons around it.HyperChemCyberChem(Lewis)videoCentral Atoms Having Less than an OctetRelatively rare.Molecules with less than an octet are typical for compounds of Groups 1A,2A,and 3A.Most typical example is BF3.Formal charges indicate that the Lewis structure with an incomplete octet is more

8、 important than the ones with double bonds.Central Atoms Having More than an OctetThis is the largest class of exceptions.Atoms from the 3rd period onwards can accommodate more than an octet.Beyond the third period,the d-orbitals are low enough in energy to participate in bonding and accept the extr

9、a electron density.HyperChem There are five fundamental geometries for molecular shape:VSEPR(Ballons)-Movie ClipFigure 9.3HyperChemSummary of VSEPR Molecular Shapese-pairsNotationName of VSEPR shapeExamples2AX2LinearHgCl2,ZnI2,CS2,CO23AX3Trigonal planarBF3,GaI3AX2ENon-linear(Bent)SO2,SnCl24AX4Tetrah

10、edralCCl4,CH4,BF4-AX3E(Trigonal)PyramidalNH3,OH3-AX2E2Non-Linear(Bent)H2O,SeCl25AX5Trigonal bipyramidalPCl5,PF5AX4EDistorted tetrahedral(see-sawed)TeCl4,SF4AX3E2T-ShapedClF3,BrF3AX2E3LinearI3-,ICl2-6AX6OctahedralSF6,PF6-AX5ESquare PyramidalIF5,BrF5AX4E2Square PlanarICl4-,BrF4-See Ng Web-siteHyperChe

11、mCyberChm GemsExamples:VSEPR Molecular Shapes-IExamples:VSEPR Molecular Shapes I F08Examples:VSEPR Molecular Shapes-IIExamples:VSEPR Molecular Shapes II F08Examples:VSEPR Molecular Shapes-IIIExamples:VSEPR Molecular Shapes III F08HyperChemExamples:VSEPR Molecular Shapes-IVExamples:VSEPR Molecular Sh

12、apes-IVThe Effect of Nonbonding Electrons By experiment,the H-X-H bond angle decreases on moving from C to N to O:Since electrons in a bond are attracted by two nuclei,they do not repel as much as lone pairs.Therefore,the bond angle decreases as the number of lone pairs increases104.5O107ONHHHCHHHH1

13、09.5OOHHHyperChemFigure 9.10:Shapes of Larger Molecules In acetic acid,CH3COOH,there are three central atoms.HyperChemShapes of Larger MoleculesIn glycine(simplest amino acid),NH2CH2CO2H,there are four possible central atoms.Draw the Lewis Structure and the 3D VSEPR Molecular Geometry for glycine.In

14、dicate the name of the shape for all possible central atoms,including estimation of bond angles.Hint 1:Designate the 2nd carbon in the formula as the central atom in skeleton structure.Hint 2:The acid portion of glycine is the same as that of acetic acid.HyperChemResonance StructuresFigure 9.12Hyper

15、ChemHyperChemHyperChem Lewis structures and VSEPR do not explain why a bond forms.How do we account for shape in terms of quantum mechanics?What are the orbitals that are involved in bonding?We use Valence Bond Theory:Bonds form when orbitals on atoms overlap.There are two electrons of opposite spin

16、 in the orbital overlap.Gems-Movie Clip To determine the electron pair geometry:draw the Lewis structure,count the total number of electron pairs around the central atom,arrange the electron pairs in one of the above geometries to minimize e-e-repulsion,and count multiple bonds as one bonding pair.F

17、ormal ChargeConsider:For C:There are 4 valence electrons(from periodic table).In the Lewis structure there are 2 nonbonding electrons and 3 from the triple bond.There are 5 electrons from the Lewis structure.Formal charge:4-5=-1.CNFormal ChargeConsider:For N:There are 5 valence electrons.In the Lewi

18、s structure there are 2 nonbonding electrons and 3 from the triple bond.There are 5 electrons from the Lewis structure.Formal charge=5-5=0.We write:CNCNCyberChm Gems Ionic BondingResonance StructuresVSEPRBasic Shapes3-D NotationHybridization(Lab)Molecular GeometriesOctet RulePolar MoleculesLewis StructuresCovalent BondingTypes of BondsChemical BondingLewisAXE notationVSEPR shapesPolarity