Valence Bond Theory
Valence Bond Theory CHM 11500 - 002
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Popular in Chemistry
This 0 page Bundle was uploaded by Allison Notetaker on Wednesday December 9, 2015. The Bundle belongs to CHM 11500 - 002 at Purdue University taught by Dr. Roy Tasker/ Dr. Scott McLuckey in Fall 2015. Since its upload, it has received 17 views. For similar materials see General Chemistry in Chemistry at Purdue University.
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Date Created: 12/09/15
LEARNING OBJECTIVES Describe the major tents of valence bond theory Valence Bond theory 0 A covalent bond forms when orbitals of two atoms overlap and a pair of electrons occupy the overlap region Wave function are in phase Central themes 0 Opposing spins of the electron pair The space formed by the overlapping orbitals has a maximum capacity for two electrons that have opposite spins Maximum overlap of bonding orbitals 0 Bond strength depends on the attraction between nuclei and shared electrons so the greater the orbital overlap the closer the nuclei are to the electrons anol the stronger the bond 0 Extent of overlap depends on orbital shape and direction Hybridization of atomic orbitals 0 During bonding the valence orbitals in the isolated atoms become new orbitals in the molecule 0 Hybridization Process of orbital mixing 0 Hybrid orbitals New atomic orbitals Features of hybrid orbitals o The number of hybrid orbitals formed equals the number of atomic orbitals mixed 0 The type of hybrid orbitals formed varies with the types of atomic orbitals mixed 0 The shape and orientation of a hybrid orbital maximize its overlap with the orbital of the other atom in the bond Understand how atomic orbitals mix to form hybrid orbitals During bonding the valence orbitals in the isolated atoms become new orbitals in the molecule Hybridization See above Ul iIEiEIquot urimtaitim EimpIi ed cf arbit l f i l39rgrbrid artham ll39llilii Halt 1th 1151 E mp illutrl an39 irlmtitlnml 1 1quot l l I 239 quotlitigantHill Triignall Li ni ar Planar Tetraheclml Eilel39 l mi al gt ht ml Hin i i l lfl HS 1 one 5 CHE J3 Liane 1 5 mixed Er awr jr threw we 1 three 1 Izlanaquot iii Elihu ii Hmrltll whims fumed Mung Ill39tim 5p El n 5191 39 Iafpl ef aim LEEquotrig mnymmm 39I i39hll i li l i il l temp 5391 iitrie fnuraquot three 139 uilama m I Step 391 l at t 39 39 lMiziilwllar shay Hangman hummule F39iiallJl39IEl 13331 Lawfiaxzytrm url Figural 1391391391 and quotagiirazmp Hybrde orbital r Elf B I1 HEM Understand how sigma and pi bonds are formed via overlap Sigma bond 0 End to end overlap 0 Has its highest electron density along the bond axis and o is shaped like an ellipse rotated about a long axis football 0 all single bonds 0 Pi bond 0 Overlap side to side 0 Two regions lobes of electron density One above and one below the sigma bond axis 0 The two electron in one pi bond occupy both lobes o A double bond consists of one sigma bond and one pi bond Increases electron density between the nuclei 0 The two electron pairs act as one electron group because each pair occupies a different orbital which reduces repulsion Know how the differing modes of overlap lead to single double and triple bonds 0 A pi bond is weaker than a sigma bond 0 Orbitals overlap less side to side than they do end to end 0 Lonepair repulsions bond polarities and other factors affect overlap between other pairs of atoms Understand why pi bonding restricts rotation about double and triple bonds 0 Sigma bond 0 Allows free rotation Because the extent of overlap is not affected E i Fig lt i 119 Tillie In ligands in ethane EEHE fling Depiction using atomic contours Er n alactnn density model shows iquot n slightly positive blue and negative real regions 1 Wedgebnndl perspective drawing 0 Pibond o Restrict rotation because p orbitals must be parallel to each other to overlap most effectively 0 Decreases the sidetoside overlap and breaks the pi bond 0 For this reasons distinct cis and trans structures exist for compounds 0 The pi bond allows two differentarrangements of atoms around some atoms Has a major effect on molecular polarity Rotation around a triple bond is not meaningful 0 Each triple bonded C atom is bonded to one other group in a linear arrangement so there can be no difference in the relative positions of attached groups Use molecular shape to determine the hybrid orbitals on the central atom in a molecule 1 Molecularformula 2 Lewis structure 3 Molecular shape and electron group arrangement 4 Hybrid orbitals Describe the types of orbitals and bonds in a molecule 0 0 Two bonding pairs Sp2 0 Three bonding pairs Sp3 o Tetrahedral electron group arrangement Sp3d o Trigonabipyramid Sp3d2 o octahedron
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