chapter 9 and 22

chapter 9 and 22 - MIDTERM 2 (covers Chapters 17, 19, 20...

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Unformatted text preview: MIDTERM 2 (covers Chapters 17, 19, 20 (+part of 4), 23, 24) (exactly as described in the syllabus + titration) April 10, 2008 (Thursday), 1:45 3:15 PM Date Time Room 148 NE 2310 N Course / Section Chem 2 / MR9E Chem 2 / MR9 Chem 2 / RISE Chem 2 / BOSC Chem 2 / MR9C Chem 2 / MR9B Chem 2 / MR9A Chem 2 / MR9D Instructor Kelebeyev Kelebeyev Kopkalli Abbasi Bhatia Wittmeyer Shakya Kahanda Apr 10, 08 1:45 3:15 PM Apr 10, 08 1:45 3:15 PM Apr 10, 08 1:45 3:15 PM Apr 10, 08 1:45 3:15 PM Apr 10, 08 1:45 3:15 PM 1127 N 3127 N 2127 N General Chemistry II, Professor Maggie Ciszkowska Molecular Geometry: Hybridization Chapter 9 Sections 9.4-9.6 General Chemistry II, Professor Maggie Ciszkowska Molecular Shapes General Chemistry II, Professor Maggie Ciszkowska Molecular Shapes In order to predict molecular shape, we assume the valence electrons repel each other. Therefore, the molecule adopts whichever 3D geometry minimized this repulsion. We call this process Valence Shell Electron Pair Repulsion (VSEPR) theory. Chemistry 1 VSEPR (review this section very carefully!) General Chemistry II, Professor Maggie Ciszkowska The VSEPR Model (Valence-Shell Electron-Pair Repulsion) helps to predict the shape of a molecule and angles between covalent bonds in a molecule 1. Draw Lewis structure. 2. Determine the number of electron pairs around the central atom. if you have a double or triple bond count it as ONE PAIR 3. Arrange electron pairs in space so as to minimize the repulsions between them (as far as possible apart from each other). 4. Describe the geometry (shape) by telling where the bonds are (not electron pairs). General Chemistry II, Professor Maggie Ciszkowska Five Fundamental Geometries for Molecules CH4 Number of electron pairs around the central atom: 4 Arrangement of bonds: tetrahedral Bond angles: 109.5 General Chemistry II, Professor Maggie Ciszkowska CH4 C 1s2 2s2 2p2 C [He] 2s2 2p2 2p 2s ...however, we have 4 identical bonds between C and H ! How can we explain this? General Chemistry II, Professor Maggie Ciszkowska CH4 C 1s2 2s2 2p2 C [He] 2s2 2p2 2p 2s .....however, we have 4 identical bonds between C and H ! How can we explain this? Idea of HYBRIDIZATION of ORBITALS (mixing of orbitals) General Chemistry II, Professor Maggie Ciszkowska Hybridization of Orbitals: CH4 1st Step: Promotion of one electron from 2s to 2p 2p 2s Now we have 4 unpaired e-. This still does not explain 4 identical bonds with H. General Chemistry II, Professor Maggie Ciszkowska Hybridization of Orbitals: CH4 1st Step: Promotion of one electron from 2s to 2p 2p 2s 2nd Step: Hybridization (mixing) of atomic orbitals There are 4 orbitals: 2s, and 3 orbitals 2p General Chemistry II, Professor Maggie Ciszkowska Hybridization of Orbitals: CH4 1st Step: Promotion of one electron from 2s to 2p 2p 2s 2nd Step: Hybridization (mixing) of atomic orbitals There are 4 orbitals: 2s, and 3 orbitals 2p Result of hybridization: 4 Hybrid Orbitals General Chemistry II, Professor Maggie Ciszkowska Hybridization of Orbitals: CH4 1st Step: Promotion of one electron from 2s to 2p 2nd Step: Hybridization (mixing) of atomic orbitals There are 4 orbitals: 2s, and 3 orbitals 2p Hybrid Orbitals: Rule 1: only orbitals with electron(s) can be hybridized Rule 2: the number of Hybrid Orbitals = = the number of original atomic orbitals that hybridize Rule 3: the energy of all hybrid orbitals is the same (they are identical), and it is somewhere between the energy of 2s and 2p orbitals. General Chemistry II, Professor Maggie Ciszkowska Hybridization Types Hybridization types: sp3 (one s orbital and three p orbitals are mixed) sp2 (one s orbital and two p orbitals are mixed) sp (one s orbital and one p obital are mixed) sp3d (one s, three p, and one d orbitals are mixed) sp3d2 (one s, three p, and two d orbitals are mixed) General Chemistry II, Professor Maggie Ciszkowska Hybridization of Orbitals: CH4 C [He] 2s2 2p2 2s Promotion 2p 2s Hybridization 4 sp3 hybrid orbitals 2p General Chemistry II, Professor Maggie Ciszkowska Hybridization sp3 Hybridization sp3: 4 sp3 Hybrid Orbitals Hybridization sp3: CH4 H 4 sp3 Hybrid Orbitals from C form 4 bonds with 4 H atoms C H Number of electron pairs around the central atom: 4 Number of bonds around the central atom: 3 Arrangement of bonds: triagonal pyramidal Bond angles: less than 109.5 NH3 Hybridization of Orbitals: NH3 N [He] 2s2 2p3 2s Promotion (nothing to promote) Hybridization 4 sp3 hybrid orbitals one with lone pair of e- 2p General Chemistry II, Professor Maggie Ciszkowska Hybridization sp3: NH3 3 sp3 Hybrid Orbitals from N form 3 bonds with 3 H atoms (1s orbitals from H atoms) 1 sp3 Hybrid Orbital has a lone pair of e- . N H H2O Number of electron pairs around the central atom: 4 Number of bonds around the central atom: 2 Arrangement of bonds: Bent Bond angles: less than 109.5 Hybridization of Orbitals: H2O O [He] 2s2 2p4 2s Promotion (nothing to promote) Hybridization 4 sp3 hybrid orbitals two with lone pairs of e- 2p General Chemistry II, Professor Maggie Ciszkowska Hybridization sp3: H2O 2 sp3 Hybrid Orbitals from O form 2 bonds with 2 H atoms 2 sp3 Hybrid Orbital have lone pairs of e- . Hybridization sp: BeF2 sp Hybrid Orbitals Consider the BeF2 molecule (experimentally known to exist). We know that the F-Be-F bond angle is 180 (VSEPR theory); linear molecule. General Chemistry II, Professor Maggie Ciszkowska Hybridization sp : BeF2 Be [He] 2s2 2s Promotion 2p 2s Hybridization 2 sp hybrid orbitals; two unhybridized orbitals remaining in Be 2p two sp hybrid orbitals Hybridization sp: BeF2 F Be 2 sp Hybrid Orbitals from Be form 2 bonds with 2 F atoms. F Hybridization sp2: BH3 Hybridization Involving d Orbitals sp3d and sp3d2 Since there are only three p-orbitals, trigonal bipyramidal and octahedral electron domain geometries must involve d-orbitals. Trigonal bipyramidal electron domain geometries require sp3d hybridization. Octahedral electron domain geometries require sp3d2 hybridization. Note the electron domain geometry from VSEPR theory determines the hybridization. General Chemistry II, Professor Maggie Ciszkowska What type of Hybridization do we have? 1. Lewis structure. 2. Determine the geometry of a molecule based on VSEPR; determine the number of bonds and electron pairs. 3. Assign hybridization based on the number of e- of the central atom, the number of identical bonds, and the number of lone e- pairs in the molecule. General Chemistry II, Professor Maggie Ciszkowska What type of Hybridization do we have? 1. SF6 2. PCl5 General Chemistry II, Professor Maggie Ciszkowska What type of Hybridization do we have? 1. SF6 6 identical bonds, octahedral geometry S [Ne] 3s2 3p4 3d 3p 3s promotion 3s 3p Hybridization sp3d2 6 hybrid orbitals sp3d2 General Chemistry II, Professor Maggie Ciszkowska What type of Hybridization do we have? 2. PCl5 5 identical bonds, trigonal bipyramidal P [Ne] 3s2 3p3 3d 3p 3s promotion 3s 3p Hybridization sp3d 5 hybrid orbitals sp3d General Chemistry II, Professor Maggie Ciszkowska Multiple Bonds -Bonds (sigma bonds): electron density lies on the axis between the nuclei. All single bonds are -bonds. -Bonds (pi bonds): electron density lies above and below the plane of the nuclei. A double bond consists of one -bond and one -bond. A triple bond has one -bond and two -bonds. Often, the p-orbitals involved in -bonding come from unhybridized orbitals. General Chemistry II, Professor Maggie Ciszkowska Multiple Bonds Hybridization: C2H4 1. Lewis structure. 2. VSEPR geometry? General Chemistry II, Professor Maggie Ciszkowska Hybridization: C2H4 1. Lewis structure. 2. VSEPR geometry? Triangular planar, double bond between two carbon atoms 3. Hybridization? General Chemistry II, Professor Maggie Ciszkowska Hybridization: C2H4 C [He] 2s2 2p2 2s Promotion 2p 2s Hybridization 1 unhybridized p orbital 3 sp2 hybrid orbitals General Chemistry II, Professor Maggie Ciszkowska 2p C2H4 Ethylene, C2H4, has: - both C atoms sp2 hybridized; - one - (sp2-sp2) and one -bond (p-p) between two C atoms; - Total of four -bonds C-H; - both C atoms with trigonal planar electron pair and molecular geometries. Multiple Bonds: CH2O Hybridization for C: sp2 Hybridization for O: sp2 3 -bonds: CO, CH, CH 1 -bond: CO General Chemistry II, Professor Maggie Ciszkowska Hybridization: C2H2 1. Lewis structure. 2. VSEPR geometry? General Chemistry II, Professor Maggie Ciszkowska Hybridization: C2H2 1. Lewis structure. 2. VSEPR geometry? Linear, triple bond between carbon atoms 3. Hybridization? General Chemistry II, Professor Maggie Ciszkowska Hybridization: C2H2 C [He] 2s2 2p2 2s Promotion 2p 2s Hybridization 2 unhybridized p orbitals 2 sp hybrid orbitals General Chemistry II, Professor Maggie Ciszkowska 2p Multiple Bonds, C2H2 Hybridization for both C: sp 3 -bonds: CC, CH, CH 2 -bonds: CC General Chemistry II, Professor Maggie Ciszkowska What hybridization do we have for all four carbon atoms in this molecule? How many and bonds total are in this molecule? H O HC1C2C3 H C1: C2: C3: C4: C4H bonds: bonds: General Chemistry II, Professor Maggie Ciszkowska What hybridization do we have for all four carbon atoms in this molecule? How many and bonds total are in this molecule? H O HC1C2C3 H C1: sp3 C2: sp2 C3: sp C4: sp C4H -bonds: 8 -bonds: 3 General Chemistry II, Professor Maggie Ciszkowska How many -bonds and how many -bonds total are there in a C2H2 molecule? General Chemistry II, Professor Maggie Ciszkowska How many -bonds and how many -bonds total are there in a C2H2 molecule? -bonds: 3 -bonds: 2 General Chemistry II, Professor Maggie Ciszkowska What hybridization do we have for all four carbon atoms in this molecule? How many - and -bonds total are in this molecule? H O H HC1C2C3 H C1: C2: C3: C4: C4 H -bonds: -bonds: H General Chemistry II, Professor Maggie Ciszkowska What hybridization do we have for all four carbon atoms in this molecule? How many - and -bonds total are in this molecule? H O H HC1C2C3 H C1: sp3 C2: sp2 C3: sp2 C4: sp2 C4 H -bonds: 10 -bonds: 2 H General Chemistry II, Professor Maggie Ciszkowska Multiple Bonds Delocalized Bonding So far all the bonds we have encountered are localized between two nuclei. In the case of benzene there are 6 C-C bonds, 6 C-H bonds, each C atom is sp2 hybridized, and there are 6 unhybridized p orbitals on each C atom; they form delocalized bonds. General Chemistry II, Professor Maggie Ciszkowska Delocalized Bonding General Chemistry II, Professor Maggie Ciszkowska Delocalized Bonding In benzene there are two options for the 3 bonds localized between C atoms or delocalized over the entire ring (i.e. the electrons are shared by all 6 C atoms). Experimentally, all C-C bonds are the same length in benzene. Therefore, all C-C bonds are of the same type (recall single bonds are longer than double bonds). General Chemistry II, Professor Maggie Ciszkowska General Conclusions Every two atoms share at least 2 electrons. Two electrons between atoms on the same axis as the nuclei are bonds. -Bonds are always localized. If two atoms share more than one pair of electrons, the second and third pair form -bonds. When resonance structures are possible, delocalization is also possible. General Chemistry II, Professor Maggie Ciszkowska Periodic Trends Chapter 22: Section 22.1 General Chemistry II, Professor Maggie Ciszkowska Size (atomic radius) increases Metallic character increases General Chemistry II, Professor Maggie Ciszkowska Ionization energy increases Electronegativity and non-metalic character increases General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska ...
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