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

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=9SXdLHTJzd6QHM&tbnid=u7WvVbJLjGUrzM:&ved=0CAUQjRw&url=http://faculty.sdmiramar.edu/fgarces/zCourse/All_Year/Ch100_MM/aMy_FileLec/04MM_LecNotes_Ch100/05_CompoundBonding/503_VSEPR/503_VSEPR.htm&ei=mSheUd-_EoWNygGd_4GoCQ&bvm=bv.44770516,d.aWc&psig=AFQjCNHtTazpMZVk23sZ8JZE351elQdM4A&ust=1365211627312627

Linear Shape (2 electron groups)

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)

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http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=-VOA70H1HXIkOM&tbnid=HGdIEx6GStUBJM:&ved=0CAUQjRw&url=http://www.northcanton.sparcc.org/~hck/data/jtp1nc/files/Chapter_23_Notes.doc&ei=SzdeUfLgGoiZyAHwzoCACw&psig=AFQjCNHBPPksXjTcrUyGSfX_7Qr-vqcUGw&ust=1365215395811773

Build the model and predict the polarity of the following:CCl4

NH3

HFC2H4