CHEM 231 - Kelly - Lecture 8-10 (Lewis Dot and VSEPR).pdf - Part A Structure and Bonding A2 Molecular Compounds A2 Molecular Compounds Goal Learning to

CHEM 231 - Kelly - Lecture 8-10 (Lewis Dot and VSEPR).pdf -...

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PartA:StructureandBonding A2:MolecularCompounds
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2 – A2:MolecularCompounds ReadChapters: 1.1to1.7,2.1to2.10,and4.18to4.20 Largelyareviewofgeneralchemistry RefreshyourknowledgeofLewisstructuresandVSEPRtheory Whydoweusechemicalmodels? To‘understandchemistry’ Todescribemolecularstructures Tointerpretandtopredictchemicalreactivity Torelatephysical/chemicalpropertieswithelectronicstructure Goal:Learningtousechemicalmodelsandtheoriesofbondingto describethestructuresofmolecules.
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3 – TheBohrModeloftheH‐Atom Bohrmodelofthehydrogenatom: Electronasaparticleorbitingaroundthenucleus Predictsthewavelengthsofemissionlines,butnotmuchelse!
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4 – Wave‐ParticleDuality Importantpoint: sometimeswetreatelectronsasparticles, oftenwetreatthemas“waves”! DiffractionofX‐raysby ametalfoil(Al,fcc) Diffractionofelectrons byametalfoil
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5 – CharacterizingWaves Amplitude istheheightofthewave: Thedistancefromnodetocrest(ornodetotrough) Amplitudeisameasureofhowintensethelightis:thelarger the amplitude,thebrighterthelight Wavelength(λ) isameasureofdistancecoveredbythewave: Thedistancefromonecresttothenext Or,thedistancefromonetroughtothenext,orthedistancebetween alternate nodes
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6 – CharacterizingWaves Frequency(ν) isthenumberofwavespassingapointinagiven periodoftime UnitsareHertz(Hz),orcyclespersecond(s −1 ):1Hz=1s −1 Energyisproportionaltothefrequencyofthewave Higherthefrequency,thegreatertheenergy
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7 – Wave‐ParticleDuality deBroglie:iflightcanbebothaparticleandawave,thenso can otherobjects electron: v =6× 10 6 m/s,wavelength~120pm proton: v =6 × 10 6 m/s,wavelength~55fm Asprinter(UsainBolt,2009WorldChampionships): v =12.4m/s m ~94kg(175pounds) Asaconsequenceofduality:theHeisenberguncertainty principle– can’tknowbothpositionandmomentumofan electronatthesametime Therefore,wedescribethe probability offindinganelectronina certainregionofspace Wavelength,λ = h / mv h =Planck’sConstant λ =5.68× 10 −37 m
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8 – 1.2– QuantumMechanics SchrödingerEquation: providesamathematicaldescriptionof electronsaswaves 𝐻 𝜓 𝑟, 𝜃, 𝜑 ൌ 𝐸𝜓 𝑟, 𝜃, 𝜑 Polar(Spherical)Coordinates SchrödingerEquation Apartialdifferentialequation Needtofindfunctions( ψ )that satisfytheequation Easiertodothisinspherical coordinates( r ,θ, φ )
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9 – TheMath… 𝐻 𝜓 𝑟, 𝜃, 𝜑 ൌ 𝐸𝜓 𝑟, 𝜃, 𝜑 SchrödingerEquation 𝑓 𝑟, 𝜃, 𝜑 1 𝑟 𝜕 𝜕𝑟 𝑟 𝜕𝑓 𝜕𝑟 1 𝑟 sin 𝜃 𝜕 𝜕𝜃 sin 𝜃 𝜕𝑓 𝜕𝜃 1 𝑟 sin 𝜃