Transcript Ch 7 Molecular Geometry

12.4 Molecular Geometry
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Lewis Dot Structures do not represent the
actual shape of molecules.
However, Lewis Dot Structures do allow us
to predict the shape of the molecule.
Predicting the 3-dimensional shape of a
molecule is called molecular geometry.
To correctly predict the shape of a
molecule, a correct Lewis structure is
essential, including non-bonded electrons.
Molecular Geometry
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The model used to predict molecular geometry is
called VSEPR
 Valence
 Shell
 Electron
 Pair
 Repulsion
The valence electron pairs surrounding an atom
(both bonding and unbonded) repel one another.
Consequently, the orbitals containing those
electron pairs are oriented to be as far away from
each other as possible.
Simple Molecular Geometry AXn
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Molecular geometry, even for the most
difficult structures, can be broken down
into a central atom surrounded by terminal
atoms.
Tables 7.5 and 7.8 give the possible
molecular geometry and angles between
bonds for molecules fitting the AXn format.
In order to determine the correct format of
AXn, you must make a correct Lewis
structure.
Primary Molecular Geometries
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BeH2 is in format AX2
Linear
molecule
OH2 is in format AX2E2
The difference is the
unshared pairs which
changes the molecular
geometry.
Bent
molecule
Primary Molecular Geometries
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BF3 is in format AX3
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NH3 is in format AX3E
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The difference is the
unshared pairs which
changes the molecular
geometry.
Triangular
planar
Triangular
pyramidal
Fun With Models
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Go to a lab station and inventory the
model kits according to the Atom Parts in
the ATOMOD 2 Brochure. Let me know if
you have less or extras!
Draw then make the following
molecules
 CH4
methane
 C2H4 ethene
 NH4+ ammonium
 CO2
carbon Dioxide