GEN CHEMISTRY I
GEN CHEMISTRY I CHEM 1201
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This 37 page Class Notes was uploaded by Malcolm Glover on Tuesday October 13, 2015. The Class Notes belongs to CHEM 1201 at Louisiana State University taught by Staff in Fall. Since its upload, it has received 28 views. For similar materials see /class/223114/chem-1201-louisiana-state-university in Chemistry at Louisiana State University.
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Date Created: 10/13/15
Chapter 9 Molecular Geometry and Bonding Theories 91 Molecular Shapes Lewis structures help us understand the compositions of molecules and their covalent bonds However Lewis structures do not show the overall shape of the molecule The shape and size of a molecule together with the strength and polarity of its bonds largely determine the properties of that substance 91 Molecular Shapes Lewis structures simply show the number and types of bonds in a molecule Cl39l gl All atoms are drawn inside the same plane In reality the actual arrangement of Cl atoms are at the corners of a tetrahedron Four equivalent faces Tetrahedron zuuP a ea39son ducepun In All CiCl bond lengths 78 A All ClgciCl angles lO9S Ball and stick model 3C14 Space filling model 92 VSEPR We can use the valenceshell electronpair repulsion VSEPR model to predict the shapes of different molecules r i Two balloons Three balloons Four balloons linear orientation trigonaleplanar orientation tetrahedral orientation mm In An optimum geometry exists for each set of balloons as they try to stay as far away from each other as possible In the same way we model molecules based on electron pair repulsion 92 VSEPR Electron domain where electrons are most likely found Bonding pair an electron domain where electrons are shared between two atoms Nonbonding pair lone pair an electron domain where electrons reside primarily on one atom Each circled pair of electrons represent a single domain even the double bonds 92 VSEPR When using VSEPR we only count the electron domains around the central atom How many electron domains does the central atom in each molecule have H N H O OO I H Sln C20 1C1 92 VSEPR When using VSEPR we only count the electron domains around the central atom How many electron domains does the central atom in each molecule have H N H O OO H4 Cl 5 21 CO 4 H q 92 VSEPR The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them TABLE 91 v ElectronDomain Geometries as a Function of Number Electron of Electron Domains Number nf Anangemenl af ElectronDomain Predicted d o m a I n Electron Domains Electron Domains Geomei Bond An les 39 39y g geom etrles 180 v ABZ linear Trigonal 120 planar so ABS trigunal planar Tetra hed ral Dali ud SHEk mudd 92 VSEPR The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them TABLE 91 ElectronDomain Geometries asaFunction of Number of EIEG I OH Dnmains Number of Arrangement of ElectronDomain Predicted Electron Domains Electron Domains Geometry Bond Angles Electron 5 mgonn 120 domain bipyramidal 90 geometries Octahcdml 90 92 VSEPR What is the electron domain geometry of the following molecules Molecule of electron domains electron domain geometry BF3 CCI4 HCI Xer 92 VSEPR The molecular geometry is the arrangement of only the atoms in a molecule or ion any non bonding pairs in the molecule are not part of the description of the molecular geometry H 1 Draw Lewis 2 Determine electron domain 3 Determine molecular structure geometry by counting all geometry by counting only electron domains then use bonding electron domains to Table 91 to determine see arrangement of bonded appropriate electron atoms trigonal pyramidal domain geomtry 2012 Pearson Educalmn inc 92 VSEPR TABLE 2 5 El Electmn Dumal eclm Dnma and Molecular Geomel 3995 for Two 111m and Four 5 around a Central Atom Number of Electron em on i Banding Nonbonding Molecular Domains Geometry Domains Domains Geometry Example 2 2 u l Linear Linear O 3 3 u Tn39gonal planar Trlgonal planar 2 1 Bent 92 VSEPR TABLE 9 EIECHDquot DDquot n and MDIEWIEF GEOITIEN I 5 far TW 111795 and Four Electron Dom 5 around a Central Atom Number of Electron Electron Domain Bonding Nonbonding Molecular Domains GBOIIlEh39V Domains Domains Geommrv Example T 4 4 0 Wham Tetrahedan H H 2112 Pman Edumiun Inn 92 VSEPR TABLE 9 a Elwlmmuamam un Mnxncularasamamas tor Five and x s Eleman Dnma mound a canal Mam Numbu of mmquot mmn Dnmaiu Banding Nnnhnnding Mulmlar Dunning Geomalzy Domain Dnmaim Gennmuy Exumyle v s 5 n d F05 J Trigvna Funny Pyramidal hnpyrmdal u a 1 qay 5F 9 Seesaw 4 a z 1 OF J Tshnpnd 1 2 3 XEF quot1 Linear 92 VSEPR YABLE 5 Elmm nmam and Mnlscnlar Gaumut os or FIVE and SIX Elaclmu Domains around a central Atom Number nf Elcchun Elulmn Dnmnin Bonding Nnnhanding Mnlmlar mm Gameuy Domain Dnmiins Gummy Earmp a s a 555 Octahedm s 1 ErFs 4 z XeF slum planar 2u12 Rwaan Edumnun Int 92 VSEPR Use the VSEPR model to predict the molecular geometry of O3 and SnCl339 1 Draw the Lewis structure of the molecule or ion and count the number of electron domains around the central atom 2 Determine the electron domain geometry 3 Use the arrangement of bonded atoms to determine the molecular geometry 92 VSEPR O3 3 electron domains TABLE 92 o ElectronDomain and Molecular Geometries for Two Three and Four Electron Domains around a Central Atom Number of Electron Eleclron Domain Bonding N onbonding Molecular Domains Geometry Domains Domains Geometry Example I 1 39F39 3 3 o ll3 at 3F Trigonal planar quot quot Trigona planar M 2 1 of 0 Bent 92 VSEPR and Molecular Geome es fov Tw 1 Electra ans quot5 around a Central Alum TAB L E Eledmn om ee and Four Number uf Electron Elec mm omam Bonding Nanbunding Molecular Domains Geometry Domains Domains Geometry Example V T 4 4 o 7 J 1 p H H H w Wham 39l errahedral 3 1 SnCI lt A 3 0 4 H H H Trigona pyramidal 91 2 2 g H H Bent 93 Molecular Shape and Molecular Polarity The polarity of a molecule is determined by what is bonded to the central atom and the symmetry of the molecule Bond dipoles that are equal in magnitude but opposite in direction cancel each other 30 NH3 Polar CC14 Nonpolar Nonpolar 93 Molecular Shape and Molecular Polarity Predict whether these molecules are polar or nonpolar a BrCl b 502 c SF6 94 Covalent Bonding and Orbital Overlap Valencebond theory uses atomic orbitals to explain bonding and to account for molecular geometry Bonding occurs when the valence atomic orbital of one atom shares space or overlaps with the valence atomic orbital of another atom 3p 35 is m gt f O 39 O lt Q Q H Ql H H V 3p 3p aaaaaaaaaaaaaaaaaaaaaa m Review for Exam 2 Questions Announcements 0 Exam 2 is on Thursday March 15th 1 hour exam 8 V2 x 11 scantron 0 Bring a pencil and scientific calculator BE ON TIME Read the rest of Chapter 9 Previously 91 Molecular Shapes so2 503 A132 bErIt A33 trigonal planar AB3 trigonal pyramidal 2012 Faersan Edumnmn In 2 C1F3 A132 linear A133 Tshaped 9 2 V S E P R TABLE 92 395 Ele Domain and Molecular Geometries for Two Three and Four o Electron Domains around a Central Atom Number of Electron Eledton Domain Bonding Nonbonding Molecular Domains Geometry Domains Domains Geometry Example 2 m 2 o I 6c6 Linear Linea 39F39 3 3 0 I B 39F r Trigonal planar quot quot Trigonal planar 2 l Bent Previously 93 Molecular Shape and Molecular Polarity 25 I313 40 Nunpulm 94 Covalent Bonding and Orbital Overlap 15 3 3p mm H 3 Il Il 95 Hybrid Orbitals Atomic orbitals on an atom mix to form new orbitals called hybrid orbitals The shape of a hybrid orbital is different from the shapes of the original atomic orbitals F is2 252 2p5 Be Be is2 252 D3 3939 in its ground state cannot bond 25 2p with the fluorine atoms because it has no unpaired electrons 1L 1 1 The Be atom can form two bonds by quotpromotingquot one of the 25 electrons to a 2p orbital 13 25 279 95 Hybrid Orbitals Atomic orbitals on an atom mix to form new orbitals called hybrid orbitals The shape of a hybrid orbital is different from the shapes of the original atomic orbitals Q Do 00 0Q One 5 atomic orbital One p atomic orbital Two 5 hybrid orbitals 5 hybrid orbitals shown together large lobes only zzzzz Pearson Enucmmn In Large lobes from two Be sp hybrid orbitals oFBeFo F 2 atomic orbital Overlap region F 2 atomic orbital 95 Hybrid Orbitals We can use VSEPR to determine the type of hybridization in a molecule TABLE 94 0 Geometric Arrangements Characteristic of Hybrid Orbital Sets Atomic Hybrid Orbital Set Orbital Set Geometry Examples sp Twosp L BeF2HgC12 152 252 9 152 251 2p 5 Threes 2 if BF 50 pp p 3 3 B 152 252 2p1 9 152 251 2p2 120 39 Trigonal planar Al sppp Four 5113 CH4 NH3 H20 NH4t C 152 252 2p2 9 152 251 2p3 Tetrahedral nnnnnnnnnnnnnnnnnnnnnn m1 95 Hybrid Orbitals We can use VSEPR to determine the type of hybridization in a molecule TABLE 94 o Geometric Arrangements Characteristic of Hybrid Orbital Sets Atomic Hybrid Orbital Set Orbital Set Geometry Examples 180 What IS the orbital sp Twosp BeFZIHgC2 me the N atom in NHZ39 spp Tiueespz 313503 1 Draw the Lewis structure Eli 2 Determine the e domain geometry 3 Specify the hybrid amp FO H SP3 CH4NHsszONH4l orbitals based on geometry Tetrahedral o 2912 Fears ooooooooooooo n 95 Hybrid Orbitals We can use VSEPR to determine the type of hybridization in a molecule TABLE 94 o Geometric Arrangements Characteristic of Hybrid Orbital Sets Atomic Hybrid Orbital Set Orbital Set Geometry Examples 180 sp Two Sp BeFZ HgCIZ Linear What is the orbital W Mr BPS503 hybridization around 1200 Trilgonal S p anar Al sppp Four 5113 CH4 NH3 H20 NH4t Tetrahedral nnnnnnnnnnnnnnnnnnnnnnn m1 96 Multiple Bonds In covalent bonds we know that the electron density is concentrated along the line connecting the nuclei the internuclear axis These bonds are called sigma 6 bonds HCl HH ClCl F BeF sp ss pp pspp To describe multiple bonding we must consider a second kind of bond resulting from the overlap between two p orbitals a pi 7t bond 96 Multiple Bonds In a 7 bond the electron density in not concentrated on the internuclear axis but lie above and below 7T bond quot Internuclear P P ONE 7 bond Although it is not evident from the picture the orientation of the p orbitals in a 7 bond makes for weaker overlap As a result it bonds are generally weaker than 039 bonds 96 Multiple Bonds H H C C H H NEN H H One a bond One a bond plus One a bond plus one 77 bond two 77 bonds C H 039 bond C C 039 bond 97 Molecular Orbitals In Chapter 6 we saw that electrons in atoms can be described by wave functions which we call atomic orbitals We now use molecular orbital theory to describe electrons in molecules by using specific wave functions called molecular orbitals MOS Characteristics of Molecular Orbitals 1 An MD can hold a maximum of two electrons 2 It has definite energy 3 M05 are associated with an entire molecule and not just an atom 97 Molecular Orbitals quot2 Destructive Nodal plane combination leads to between nuclei antibonding H2 molecular orbital gt1 715 Energy M 5 1s H atomic orbitals 015 H2 molecular orbitals Concentrated Constructive electron density combination leads to between nuclei bonding H2 molecular orbital 2u12 Pearson Education Inc 97 and 98 Molecular Orbital Diagrams for Diatomic Molecules Draw the molecular orbital diagram for each molecule What is the bond order for each H2 Li2 C2 F2 He2 Be2 N2 Ne2 Hez B2 02 Announcements Read Chapter 101 103
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