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Chapter 9 Chemical Bonding
Section 9.2 Molecular Shape and Polarity
The Shapes of MoleculesThe shape of a molecule and the polarity of
its bonds determine whether the molecule as a whole is polar.
The shape is important in predicting properties and how the molecule reacts with other molecules
The Shapes of MoleculesModels help us visualize the 3D structures of
molecules.
Lewis Dot StructureReview groups – what is the number we want?
Draw the Lewis dot structures of the following:CH4
NH3
CO2
H2CO
Double Bond- a bond formed by sharing two pairs of electrons between two atoms
Triple Bond- a bond formed by sharing three pairs of electrons between two atoms
ShapesLinear
Trigonal PlanarTrigonal PlanarBent
TetrahedralTetrahedralTrigonal PyramidalBent
Trigonal Shape (3 electron groups)Trigonal Planar Bent
Tetrahedral (4 electron groups)
Tetrahedral
Trigonal Pyramid
Bent
Lone pair electronsDistort the shape of moleculesExample: Tetrahedral geometry
No lone pairs One lone pair Two lone pairs
CH4 NH3 H2O
Steps in Creating a 3-D model1) Draw Lewis structure2) Count the # of bonds and lone pair
electrons on the central atom3) Select geometric category4) Place electrons and atoms that lead to most
stable arrangement ( minimize e-repulsions)5) Determine 3-D
Some ModelsCreate the following models (pg 323)
HClCH4
NH3
H2O
C2H6
Polar and Non-Polar Molecules
Polarity is important, just like shape, in affecting the properties of compounds. They
act TOGETHER.
Polar and Non-PolarPolar molecule – MOLECULE has a positive and negative pole. (Different ENs) - Dipole
Non-polar molecule– MOLECULE share electrons equally. (Same ENs)
Build the model and predict the polarity of the following:CCl4
NH3
HFC2H4