L16S07_FormalCharge_VSEPR 2-23-07

L16S07_FormalCharge_VSEPR 2-23-07 - L16"Formal...

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Unformatted text preview: L16: "Formal Charge,Oxidation numbers,VSEPR Theory" Chemical Bonding Ionic: More electronegative element captures e- + Li :F: Resonance, Bond Order Ozone Covalent: Electrons shared equally 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 : : Share electrons equally:. N . (5) Compare to atoms: Lewis Dot Structure: O: N :O: : : - : : O: (7) .N . (5) 0 : : : : O: (6) Formal Charge: 2004Kubinec,Pines,Nitsche 2001 UC Regents -1 L4-11 L16-1 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 L16-2 ChemQuiz 16.01 What is the S-O bond order in the sulfate ion? O O O O -2 S 1) 1 2004Kubinec,Pines,Nitsche 2) 1.5 3) 2 L16-3 2004 Kubinec, Pines, Nitsche 1 L16: "Formal Charge,Oxidation numbers,VSEPR Theory" Summary Molecular Structure and Geometry H H C H H C O H H Steric Number = #LP + # bonded atoms 2004Kubinec,Pines,Nitsche L16-6 Valence-Shell Electron Pair Repulsion (VSEPR) Model Shapes Valence2 3 : : : : linear trigonal planar 180 180 120 120 109.5 109.5 4 tetrahedral 120 trigonal 120 bypyramidal 90 90 Steric Number = # lone e-pairs + e# bonded atoms 5 6 octahedral 90 90 90 90 L16-7 2004Kubinec,Pines,Nitsche 2004 Kubinec, Pines, Nitsche 2 L16: "Formal Charge,Oxidation numbers,VSEPR Theory" 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 pairs around central atom Determine position of atoms from the ways electrons are shared and arrange them so as to minimize repulsion Name the molecule structure from the 2004Kubinec,Pines,Nitsche L16-8 position of the atoms Linear O C O Cl B Cl+ 2004Kubinec,Pines,Nitsche L16-9 Trigonal planar F F B F Multiple bonds count as one effective e pair 2004Kubinec,Pines,Nitsche L16-10 2004 Kubinec, Pines, Nitsche 3 L16: "Formal Charge,Oxidation numbers,VSEPR Theory" Tetrahedral : : O H 104.5H 104.5 Tetrahedral electron arrangement but V-shape H 109.5 109.5 H C H H 2004Kubinec,Pines,Nitsche Lone e-pairs compress the eangle between bonding pair H NH 107H 107 L16-11 .. Trigonal bipyramidal Cl Cl Cl P Cl Cl F : :I F F 2004Kubinec,Pines,Nitsche L16-12 Xenon Tetrafluoride Crystals Source: Argonne National Laboratory 2004Kubinec,Pines,Nitsche L16-13 2004 Kubinec, Pines, Nitsche 4 L16: "Formal Charge,Oxidation numbers,VSEPR Theory" Octahedral Octahedral electron arrangement but square planar structure F .. Xe F .. F F F 2004Kubinec,Pines,Nitsche F F S F F F L16-14 ChemQuiz 16.2 For the molecular ions: SiH3+ CCl3 SiH Compare the bond angles: Y 1 (H-Si-H) 2 (Cl-C-Cl) SiCl- Cl) 1) 1 = 2 2004Kubinec,Pines,Nitsche Y X Y 2) 1 < 2 3) 1 > 2 L16-15 ChemQuiz 16.3 Which of the following molecules or ions is linear? linear? Y X Y 1) ICl2 2004Kubinec,Pines,Nitsche - 2) BrF2+ BrF + 3) H2S L16-17 2004 Kubinec, Pines, Nitsche 5 L16: "Formal Charge,Oxidation numbers,VSEPR Theory" ChemQuiz 16.4 In the following acid-base acidreaction, which species has the largest bond angle? angle? H3O+ + NH3 1) H3O + 2004Kubinec,Pines,Nitsche NH4+ + H2O + 3) NH4 L16-19 2) NH3 Lecture Complete 2004Kubinec,Pines,Nitsche L16-21 2004 Kubinec, Pines, Nitsche 6 ...
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