L14S08 VSEPR - L14"VSEPR Theory" Chemical Bonding...

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Unformatted text preview: L14: "VSEPR Theory" Chemical Bonding More electronegative element captures e- Ionic: + Li :F: Resonance, Bond Order Ozone Electrons shared equally Covalent: Previously + :Cl: Cl : : : : : : : No Dipole : : : : Electronegativity O O+ - O- -O +O O O C O -2 O O C 1 O 1 3 O 1 Polar Covalent: Unequal sharing, Dipole moment + Dipole, symmetry Dipole, Dipole Carbonate - O O C O O OC O - - O O- O H Cl: Cl: - : : Benzene L4-4 2000 A.Pines M.Kubinec UCB L3-11 2001 UC Regents (`covalent' electron distribution) Formal Charge : : Lewis Dot Structure: Share electrons equally: .N . (5) O: N :O: : : - : : O: (7) Compare to atoms: .N . (5) 0 : : O: (6) Formal Charge: 2004Kubinec,Pines,Nitsche 2001 UC Regents -1 L4-11 L14-1 Rules for FORMAL CHARGE (FC) FC = # Valence e- free atom - # Valence e- atom molec. molec. Assign LONE PAIRS entirely TO ATOM SHARED ELECTRONS are DIVIDED EQUALLY between sharing atoms Atoms in molecules try to have FORMAL CHARGES AS CLOSE TO ZERO AS POSSIBLE NEGATIVE FORMAL CHARGES must be WITH MOST ELECTRONEGATIVE ATOMS 2004Kubinec,Pines,Nitsche L14-2 ChemQuiz 13.1 Which of the following is the `best' best' structure for the sulfate ion, SO42-? A) O O 2004Kubinec,Pines,Nitsche B) O O S O O C) O O S O O L14-3 O S O 2004 Kubinec, Pines, Nitsche 1 L14: "VSEPR Theory" Summary Molecular Structure and Geometry H H C H H C O H H Steric Number = #LP + # bonded atoms 2004Kubinec,Pines,Nitsche L14-5 Valence-Shell Electron Pair Repulsion (VSEPR) Model Shapes ValenceSteric # 2 3 : : linear trigonal planar 4 tetrahedral trigonal 5 bypyramidal Steric Number = # lone e-pairs + e# bonded atoms 6 octahedral 2004Kubinec,Pines,Nitsche L14-6 2004 Kubinec, Pines, Nitsche 2 L14: "VSEPR Theory" Octahedral Octahedral electron arrangement but square planar structure F F .. Xe .. F F F 2004Kubinec,Pines,Nitsche F F S F F F L14-7 Trigonal bipyramidal Cl Cl Cl P Cl Cl F : :I F F 2004Kubinec,Pines,Nitsche L14-8 Tetrahedral H H C H H 109.5 109.5 2004Kubinec,Pines,Nitsche L14-9 2004 Kubinec, Pines, Nitsche 3 L14: "VSEPR Theory" Trigonal planar F F B F Multiple bonds count as one effective e pair 2004Kubinec,Pines,Nitsche L14-10 Linear O C O Cl B Cl+ 2004Kubinec,Pines,Nitsche L14-11 Molecular Shapes 2 3 1 lone pair 2 lone pairs linear trigonal planar 120 120 109.5 109.5 4 tetrahedral 120 trigonal 120 5 bypyramidal 90 90 90 90 90 6 octahedral 90 2004Kubinec,Pines,Nitsche Table 10.1 in Tro L14-12 2004 Kubinec, Pines, Nitsche 4 L14: "VSEPR Theory" Effect of Lone Pairs Electron group repulsions: Lone pair-lone pair > lone pair-bonding pair > pairpairbonding pair-bonding pair pair 2004Kubinec,Pines,Nitsche L14-13 Steps for Using the VSEPR Model Draw Lewis structure for the molecule Use any of the resonance structures to predict molecular structures Count each multiple bond as a single effective pair Count electron groups around central atom Determine electronic shape Arrange electron groups to minimize repulsion Determine molecular shape from the position of the atoms 2004Kubinec,Pines,Nitsche L14-14 ChemQuiz 14.1 For the molecular ions: SiH3+ CCl3SiH Compare the bond angles: Y 1 (H-Si-H) 2 (Cl-C-Cl) SiCl- Cl) A) 1 = 2 2004Kubinec,Pines,Nitsche Y X Y B) 1 < 2 C) 1 > 2 L14-15 2004 Kubinec, Pines, Nitsche 5 L14: "VSEPR Theory" ChemQuiz 14.2 Which of the following molecules or ions is linear? linear? Y X Y A) ICl2 2004Kubinec,Pines,Nitsche B) BrF2+ BrF C) H2S L14-16 ChemQuiz 14.3 In the following acid-base acidreaction, which species has the largest bond angle? angle? H3O+ + NH3 A) H3O + 2004Kubinec,Pines,Nitsche NH4+ + H2O + C) NH4 L14-17 B) NH3 Lecture Complete 2004Kubinec,Pines,Nitsche L14-18 2004 Kubinec, Pines, Nitsche 6 ...
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