Chapter 9 -Chapter 10

Chapter 9-Chapter - General Chemistry I Fall 2007 Joann S Monko Chemistry 9th ed Raymond Chang Violations of the Octet Rule Usually occurs with

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Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang Violations of the Octet Rule Usually occurs with B & elements of higher periods. 2 BF3 SF4 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Boron Trifluoride Central atom = _____________ Valence electrons = __________ or electron pairs = __________ Assemble dot structure The B atom shares in only 6 e-`s (or 3 pairs). B atom is electron deficient. 3 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Central atom = Valence electrons = ___ or ___ pairs. Form sigma bonds and distribute electron pairs. 5 pairs around S atom. Common - outside the 2nd period. Sulfur Tetrafluoride, SF4 4 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 5 Clicker Question Write the Lewis structure for XeF4. There are ___ around Xe. a. 4 single bonds b. 4 single bonds & 1 lone e- pair c. 4 single bonds & 2 lone e- pairs d. 2 single bonds, 2 double bonds & 1 lone e- pair MOLECULAR GEOMETRY 6 VSEPR Valence Shell Electron Pair Repulsion theory. Most important factor in determining geometry is relative repulsion between electron pairs. Molecule adopts the shape that minimizes the electron pair repulsions. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Needed Info... A = central atom X = outer atoms E = e- pair CED = center of e- density place where you find electrons 1 CED = a single, a double, a triple bond or a lone e- pair 7 Hybridized Orbitals a new set of orbitals created by mixing atomic orbitals s, p and d. orbitals that are used in bonding 2 CED = sp 3 CED = sp2 4 CED = sp3 5 CED = sp3d 6 CED = sp3d2 Needed Info... Electron Geometry Determined by the hybridized orbitals how the e-`s arrange themselves to be as far away from each other as possible. e-`s are not visible but are still repulsive. Molecular Geometry how the molecule appears what you see = atoms what you don`t see = lone electron pairs 8 9 Chemistry, 8th ed. Chang 10 Chemistry, 8th ed. Chang Formation of sp2 11 Chemistry, 8th ed. Chang Formation of sp 12 Chemistry, 8th ed. Chang 13 Electron Pair Geometries Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 14 No. of e- Pairs Around Central Atom 2 Example F--Be--F 180 F Geometry linear 3 F B 120 planar trigonal F 4 H H C 109 tetrahedral H H Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. No. of e- Pairs Around Central Atom 2 15 Example F--Be--F 180 F Geometry linear 3 F B 120 planar trigonal F 4 H H C 109 tetrahedral H H Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. No. of e- Pairs Around Central Atom 2 16 Example F--Be--F 180 F Geometry linear 3 F B 120 planar trigonal F 4 H Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. H C 109 tetrahedral H H Electron Pair Geometries 17 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Geometries for Four Electron Pairs 18 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Boron Compounds boron trifluoride, BF3 The B atom is surrounded by only 3 electron pairs. 3 CED`s sp2 hybridized orbitals Bond angles are 120o Geometry: 19 F F B F trigonal planar Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Ammonia, NH3 1. Draw electron dot structure 2. Count BP`s and LP`s = 4 CED`s Structure Determination by VSEPR 20 H N H H 3. The 4 electron pairs are at the corners of a tetrahedron. N H H H Hybrid Orbitals = sp3 lone pair of electrons in tetrahedral position E- pair geometry = Td Molecular geometry = trigonal pyramidal Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Structure Determination by VSEPR Water, H2O 1. Draw electron dot structure 2. Count BP`s and LP`s = 4 CED`s 3. The 4 electron pairs are at the corners of a tetrahedron. sp3 hybridized orbitals 21 The electron pair geometry is TETRAHEDRAL. The molecular geometry is BENT. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Structure Determination by VSEPR Formaldehyde, CH2O 1. Draw electron dot structure 2. Count BP`s and LP`s at C = 3 CED`s sp2 hybridized orbitals The e- pair geometry & molecular geometry is PLANAR TRIGONAL with 120o bond angles. 22 O H C H O C H H Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Structure Determination by VSEPR Methanol, CH3OH Define H-C-H and C-O-H bond angles H 23 #1 H-C-H = 109o #2 C-O-H = In both cases the atom is surrounded by 4 e- pairs. #1 C is the central atom 4 CED`s = sp3 hybridization Td e- pair & molecular geometry #2 O is the central atom 4 CED`s = sp3 hybridization Td e- pair geometry Bent molecular geometry (AX2E2) H--C--O--H o 109 H 109 109 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Structure Determination by VSEPR Acetonitrile, CH3CN #1 H-C-H = 109o #2 C-C-N = 180o H 24 H--C--C N 109 H 180 #1 C is the central atom 4 CED`s = sp3 hybridization Td e- pair & molecular geometry #2 C is the central atom 2 CED`s = sp hybridization Linear e- pair & molecular geometry Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 25 Phenylalanine, an amino acid H C H C C H C H 1 C C H H 2 H C H C N H O C H 5 3 O 4 H Phenylalanine 26 27 Molecular Geometries for Five Electron Pairs 28 Compounds with 5 Pairs Around the Central Atom 90 F F P F AX5 5 CED`s sp3d hybridized orbitals Trigonal bipyramid F F 120 Sulfur Tetrafluoride, SF4 Number of valence e-`s = 34 Central atom = S Dot structure 5 CED`s sp3d hybrid orbitals 90 F F 29 S F F Molecular Geometry = Seesaw Electron pair geometry --> trigonal bipyramid F S F F F Lone pair is in the equator cuz it requires more room. 120 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 30 Molecular Geometries for Six Electron Pairs Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 31 Compounds with 6 Pairs Around the Central Atom 90 F F F AX6 6 CED`s sp3d2 hybridized orbitals Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. F S Octahedron F F 90 Formal Atom Charges 32 Atoms in molecules can have a charge (+ or -). The predominant resonance structure: charges are as close to 0 as possible. Formal charge = Group # (# of Bonds) - (# of LP e-'s) Carbon Dioxide CO2 6-2-4=0 O C O Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 4-4-0=0 Thiocyanate Ion, SCN- 33 6 - 1 - 6 = -1 5-3-2=0 S C 4-4-0=0 N Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 34 Thiocyanate Ion, SCN S C N S S C N C N Which is the most important resonance form? Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 35 Boron Trifluoride, BF3 F B + - F F What if we form a B--F double bond to satisfy the B atom octet? Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. ...
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This note was uploaded on 04/08/2008 for the course CHEM 100 taught by Professor Monko during the Winter '08 term at Kutztown.

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