Download Section 8.4 Molecular Shapes VSEPR Model • The shape of a

Section 8.4 Molecular Shapes
• Summarize the VSEPR bonding theory.
• Predict the shape of a molecule.
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VSEPR Model
• The shape of a molecule determines many of its
physical and chemical properties.
• Molecular geometry (shape) can be determined
with the Valence Shell Electron Pair
Repulsion model, or VSEPR model which
minimizes the repulsion of shared and unshared
atoms around the central atom.
Section 8.4 VSEPR Model (cont.)
• Electron pairs repel each other and cause
molecules to be in fixed positions relative to
each other.
• Unshared electron pairs also determine the
shape of a molecule.
• Electron pairs are located in a molecule as far
apart as they can be.
Section 8.4 VSEPR Model (cont.)
• Start with the central atom.
• Identify how many bonds or shared pairs
are on the central atom.
• Then identify how many unshared pairs
or lone pairs are on the central atom.
• Each combination of shared and unshared
pairs will represent a specific molecular
shape.
Section 8.4 Shapes of Molecules
Section 8.4 Shapes of Molecules (cont.)
Section 8.4 Shapes of Molecules (cont.)
Shapes of Molecules (cont.)
• Remember to focus on the central atom.
Here is a review of the shapes:
Linear- 1 bond, no central atom
- 2 bonds, no unshared pairs of eBent- 2 bonds, 2 unshared pairs of ePyramidal- 3 bonds, 1 unshared pair of eTriangular planar or Trigonal3 bonds, no unshared pair of eTetrahedral- 4 bonds, no unshared pair of eTrigonal Bipyramidal5 bonds, no unshared pair of eOctahedral- 6 bonds, no unshared pairs of e-
AB2
AB2E2
AB3E
AB3
AB4
AB5
AB6
Shapes of Molecules (cont.)
Predicting the Shape of Molecules
Steps:
1. Draw the Lewis Structure for the compound.
2. Identify the central atom as A.
3. Identify the number of bonds (B) around the
central atom. Use a subscript to label the
number.
4. Identify the number of unshared pairs of
electrons (E) on the central atom.
Write out the abbreviations and figure out the shape.