11/1/2013

Today:
◦ Summary of Lewis Dot
Structures
◦ VSEPR Theory:
 Electron Regions: Bonding e- &
Lone Pairs
 Shapes:
 Linear
 Trigonal Planar vs. Bent
 Tetrahedral vs. Trigonal
Pyramidal vs. Bent

Schedule an appointment or
stop by office hours to pick up
Midterm Exam 2

Next Meeting
◦ Concept Check:
 Covers today’s material
◦ Please read Chapter 10, pp.
340-348 before Thursday
iClicker Participation Question:
Recognizing CORRECT & INCORRECT Lewis Dot Structures
Select the Lewis Dot Structures below that are VALID.
A.
B.
C.
D. ALL of these Lewis Dot Structures are VALID
E. NONE of these Lewis Dot Structures are VALID
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11/1/2013
Lewis Dot Structures for Polyatomic Ions:


6.
For each negative (-) charge: add one electron.
For each positive (+) charge: subtract one electron.
If needed, move lone pairs from outer atoms to bond with the
central atom to form an octet on the central atom.
 This will make double or triple bonds.
Valence Shell Electron Pair Repulsion (VSEPR) Theory:
Molecules and polyatomic ions take on particular shapes based on
the number of electron regions located around a central atom:
• Valence Shell (VS…): Consider ONLY the valence electrons:
• Lone pair electrons & bonding electrons are all treated the
same:
• A single bond counts the same as a double or triple bond
• Lone pairs are considered the same as bonding electrons
• Electron Pair Replusions (…EPR): electrons are negative charges
that naturally REPEL from other electrons. These repulsive forces
between electrons determines molecular shape.
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11/1/2013
LINEAR Molecular Geometry
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
2
2
0
The Total Number of Electron
Regions determines the Electron
Geometry:
180°
2 REGIONS = LINEAR GEOMETRY
Linear
LINEAR Molecular Geometry
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
2
2
0
180°
Linear
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11/1/2013
TRIGONAL PLANAR Molecular Geometry
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
3
3
0
120°
Trigonal planar
TRIGONAL PLANAR Electron Geometry
BENT MOLECULAR GEOMETRY
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
3
2
1
The Total # of Electron Regions
determines the Electron
Geometry:
3 REGIONS = TRIGONAL
PLANAR Electron Geometry
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11/1/2013
TRIGONAL PLANAR Electron Geometry
TRIGONAL PLANAR MOLECULAR
GEOMETRY
When lone pairs are present on the central atom, the
molecular geometry is DIFFERENT from the electron
geometry.
• Molecular Geometry only considers the positions
of the atoms
TRIGONAL PLANAR Electron Geometry
BENT MOLECULAR GEOMETRY
4 REGIONS = TETRAHEDRAL Electron Geometry
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
4
4
0
109.5°
Tetrahedral
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4 REGIONS = TETRAHEDRAL Electron Geometry
ONE LONE PAIR = TRIGONAL PYRAMIDAL MOLECULAR GEOMETRY
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
4
3
1
109.5°
Tetrahedral
Trigonal Pyramid
4 REGIONS = TETRAHEDRAL Electron Geometry
TWO LONE PAIRS = BENT MOLECULAR GEOMETRY
Electron Dot
Structure
Total # of
ELECTRON
Regions
# of
BONDING
Regions
# of
LONE PAIRS
4
2
2
109.5°
Tetrahedral
Bent
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11/1/2013
iClicker Participation Question:
Predicting Bond Angles in THC
What is the bond angle between the highlighted carbons, C—C—C?
A. 90o
B. 109.5o
C. 120o
D. 180o
E. It depends
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