CHAPTER 9: MOLECULAR
GEOMETRY AND BONDS
JANUARY 28TH, 2013
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Do Now:
Calculate the ∆H:
C2H4 + HCN  CH3CH2CN
MOLECULE SHAPE
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How do we determine the shape of a molecule?
How are bonds related to the location of
electrons?
Draw CO2, how many electron domains are
located on the central carbon?
VSEPR THEORY
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States: “Best arrangement of a given number of
electron domains is the one that minimizes the
repulsions among them”
Predict the difference between electron-domain
geometry and molecular geometry.
How do we use VSEPR Theory:
Draw lewis structure of molecule or ion and count number
of electron domains around central atom.
 Determine electron-domain geometry
 Using table determine (eventually *memorize*) molecular
geometry
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PRACTICE
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Predict the molecular geometry of:
O3
 SnCl3
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Compare and contrast:
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H2O
CH4
NH3
Explain the ideal bond angles.
WORK IT OUT
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How are all the bond angles related to one
another?
With a partner or small group, discuss why it is
possible that all these angles are so large,
similar.
In fancy terms: Non-bonding electrons give off
greater repulsive forces therefore compressed
bond angles.
** NOTE: double bonded atoms tend to exert a
greater repulsive force as well.
PRACTICE:
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Determine the following molecular geometries:
SF4
 IF5
 BrF3
 ICl4
LARGER THAN LIFE…
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Large molecules need to be broken down into
their smaller components:
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Draw CH3COOH (use VSEPR for each central atom)
POLARITY
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Why is polarity important?
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How do we determine polarity?
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Bonds:
Molecules:
Predict the polarity of the following:
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BrCl
SO2
SF6
EXPLANATIONS
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How do we explain bonding?
How is energy related to distance of covalent
bonds?
Why is there a sharp increase with shorter
distance?
All in all: bond length is distance at which the
attractive forces between unlike charges are
balanced by repulsive forces within the molecule