Chapter 13 Molecular Shapes VSEPR Theory

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Chapter 13Molecular ShapesVSEPR Theory
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Molecular Shape

• Molecular shape or molecular geometry is the
  three-dimensional arrangement of the atoms in a
  molecule.

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Molecular Shape

• Molecular shape determines several properties of
  a substance including
• reactivity
• polarity
• phase of matter
• color
• magnetism
• biological activity

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Olfaction sense of smell

• Lock-and-Key Theory humans can smell various
  odors because each three-dimensional odor
  molecule fits into only one type of receptor.

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Gustation the sense of taste

• Taste receptors are located on the tongue and are
  sensitive to four major tastes salty, sweet,
  sour and bitter.
• Taste receptors respond differentially to the
  varying shapes of food and liquid molecules.

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H2
2(1) 2e-
H
H
Any 2 atoms linear

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What about molecules consisting of more than two
atoms

• For this we must use the VSEPR Theory

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VSEPR Theory

• Valence Shell Electron Pair Repulsion Theory
• Predicts the molecular shape of a bonded molecule
  containing a central atom(s).
• Electrons around the central atom arrange
  themselves as far apart from each other as
  possible
• So only electrons (lone pairs or bonds) connected
  to the central atom are important.

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Five Molecular Shapes

• See the table in your notes

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Steps in Determining Molecular Shape

1. Draw the Lewis Structure for the Molecule.
2. Count the number of atoms attached to the central
   atom.
3. Count the number of lone pairs attached to the
   central atom.
4. Use your counts on steps 2 and 3 to determine the
   shape of the molecule.

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H2S
2(1)6 8e-

• Dihydrogen monosulfide is commonly known as sewer
  gas. This colorless, toxic and flammable gas is
  responsible for the foul odor of rotten eggs.

2/2 angular
H
H
S

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H2S

• Dihydrogen monosulfide is commonly known as sewer
  gas. This colorless, toxic and flammable gas is
  responsible for the foul odor of rotten eggs.

S
H
H
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Methane (CH4)
4 4(1) 8e-
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Methane (CH4)
4 4(1) 8e-
4 atoms attached to the central atom. 0 lone
pairs on the central atom. 4/0
Tetrahedral shape
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Methane (CH4)
4 4(1) 8e-
4 atoms attached to the central atom. 0 lone
pairs on the central atom. 4/0
Tetrahedral shape
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HCN
145 10e-


H
N
C



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HCN
145 10e-


H
N
C



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HCN
145 10e-


H
N
C



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HCN
145 10e-


H
N
C

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HCN
145 10e-


H
N
C

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HCN
145 10e-

H
N
C
2/0 linear
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H2S


S
H
H
2/2 angular
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SO2
62(6) 18e-



O
O
S





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SO2
62(6) 18e-



O
O
S





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SO2
62(6) 18e-



O
O
S





2/1 angular
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CH4
4/0 tetrahedral
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NO3-
53(6)1 24e-



O
O
N




O



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NO3-
53(6)1 24e-



O
O
N




O



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NO3-
53(6)1 24e-



O
O
N




O



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NO3-
53(6)1 24e-
-


O
O
N




O
3/0 trigonal planer



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SOCl2
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SOCl2
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Draw the Lewis structure for an acetate ion?
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Draw the Lewis structure for an acetate ion?
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Whats the shape of acetate?
3/0 trigonal planer
4/0 tetrahedral
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Homework

• Worksheet Chapter 13.
• Study Guide Chapters 12 14 (due by the end of
  the week).