Chapter 9 Chemical Bonding Section 9.2 Molecular Shape and Polarity

The Shapes of Molecules The 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 Molecules Models help us visualize the 3D structures of molecules.

Lewis Dot Structure Review 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

Shapes Linear Trigonal Planar Bent Tetrahedral Trigonal Pyramidal

Linear Shape (2 electron groups)

Trigonal Shape (3 electron groups) Trigonal Planar Bent

Tetrahedral (4 electron groups) Bent Trigonal Pyramid

Lone pair electrons Distort the shape of molecules Example: Tetrahedral geometry No lone pairs One lone pair Two lone pairs CH4 NH3 H2O

Steps in Creating a 3-D model Draw Lewis structure Count the # of bonds and lone pair electrons on the central atom Select geometric category Place electrons and atoms that lead to most stable arrangement ( minimize e-repulsions) Determine 3-D

Some Models Create the following models (pg 323) HCl CH4 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-Polar Polar 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 HF C2H4