Lec' 10 Lewis Dot Structures

1
Fred J. Grieman
Lec. 10 Lewis Dot Structures
Multiple bonds Resonance
Structures Formal Charge
Valence Shell Electron Pair Repulsion
Molecular Structure HW Review Problems
for Exam Redo Statistics Problems
1 5, 9, 17, 23, 33, 36be, 41, 42, 64, 74
2 3, 9c, 18, 20, 28, 35, 51
3 3, 7, 13, 15, 24, 25, 28, 35, 37, 42, 43
You do not need to turn these in. The
graders will not have time to grade
return them before the exam.
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• Text Method for Lewis Dot Structures
• A Total of Valence Electrons
• 2) N of e-s for all noble gas config.s
• 3) S N A Shared Pairs
• 4) 2 Bonding e-s btwn each atom
• 5) Bonding e-s remaining ? double /or triple
  bonds
• 6) Remaining e-s are lone pairs
• Resonance Structures
• Hybrid of all equivalent structures. Multiple
  Bonds DO NOT hop around
• Formal Charge (F.C.)
• 1) F.C. on atom ( l.p. e-s ½ s.p. e-s
  G. )
• 2) Reduce F.C. with multiple bonds when allowed
  (lowest F.C. is best)
• 3) F.C. on more electronegative atom F.C.
  on more electropositive atom
• 4) Check S F.C. molecules charge
• Valence Shell Expansion Great than octet okay
  for 3rd Row

FIRST EXAM
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• Valence Shell Electron Pair
  Repulsion
• Lewis Dot Structures
  Molecular Structure
• VSEPR
  (Positions of atoms
• 
  
  bond angles distances)
• Basis e- pairs (EP) repel each other ?
• equilibrium structure result of
  minimized repulsion
• Bonding Pairs (BP) Lone Pairs (LP) ? 3
  different interactions
• 2) E(BP ? BP) lt E(BP ? LP) lt E(LP ? LP)
• 
  
  
  
  ..
• 3) Reasoning BP nuc - - nuc LP
  nuc - A - B
• 
  directed btwn 2 nuclei
  more spread out
• 
  B
• VSEPR Method
• Draw Correct Lewis Dot Structure
• Determine Steric Number (SN atoms bonded to
  l.p.s on central atom)
• Use EP Structure that minimizes EP repulsion
• Arrange BP LP to minimize energy
• Determine Molecular Geometry from atom positions

large
medium
small
SN ? 4
4
Molecule Lewis Dot SN
EP Structure Molecular Structure
.. .. OCO
CO2
O-C-O Linear bond
angle? 180
2
Linear
Trigonal Planar bond angle?
120
O .. .. OSO
SO3
3 Trigonal planar
Bent bond angle ? ?
120 (119.5)
..
.. .. .. OSO
3 Trigonal planar
SO2
Bent bond
angle? ? 120 (117.5 )
..
.. .. .. O?OO
3 Trigonal planar
O3
VSEPR
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Molecule Lewis Dot SN EP Structure
Molecular Structure
H H ? C ? H H
CH4
H H \ / Tetrahedral C ?
?H H bond
angle ? 109.5
4 Tetrahedral
.. N Trigonal
Pyramid H ?? ?H H
bond angle ?
lt 109.5 (107.3)
.. H ? N ? H H
NH3
4 Tetrahedral
..
..
Bent bond angle ? lt 109.5 lt107.3 ? (104.5)
.. H ? O ? H
H2O
4 Tetrahedral
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Molecule Lewis Dot SN EP
Structure Molecular Structure
F F F P F F
F Trigonal Bipyramid F
different angles F?P? ?F
90 120 F
PF5
5 Trigonal Bipyramid
120
90
90 interactions only important ones F
F axial r(PF)1.577Å F?P?
?F equatorial F
r(PF)1.534 Å
F F .. S F F
5 Trigonal Bipyramid
F F Seesaw S? ?F F
SF4
in axial or equatorial position? E(LP?BP)gtE(BP?B
P) Only 90 important
F F ?S? ?F F two 90
LP ? BP
.. F F?S? ?F
F three 90 LP ? BP
F Disorted Seesaw / F
? S? bond angle lt180 \?F
(173) F
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Molecule Lewis Dot SN EP
Structure Molecular Structure
F .. Cl F F
ClF3
F .. T-Shape F?Cl?
angle lt 90? ?.. (87.5?)
F
5 Trigonal Bipyramid
I .. Linear? ? I? ?..
no 90? LP ? LP I
.. .. .. .. I ? I ? I
I3-
5 Trigonal Bipyramid
F F F S F F F
F F F Octahedral ?S? F
?F F
6 Octahedral
SF6
?
F F F Square Pyramid
?Br? F ?F
F F F Br F F
BrF5
6 Octahedral All positions equivalent
?
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Molecule Lewis Dot SN EP
Structure Molecular Structure
F F .. I F
F
.. F F Square Planar ?I ?
Bond Angle 90 F F
6 octahedral E(LP ? LP) the largest
IF4-
?
?