Molecular Polarity Molecular Structure

Presentation on theme: "Molecular Polarity Molecular Structure"— Presentation transcript:

1 Molecular Polarity Molecular Structure
Courtesy Christy Johannesson

2 + - Dipole Moment H Cl Direction of the polar bond in a molecule.
Arrow points toward the more electronegative atom. H Cl + - Courtesy Christy Johannesson

3 Determining Molecular Polarity
Nonpolar Molecules Dipole moments are symmetrical and cancel out. BF3 F B Courtesy Christy Johannesson

4 Determining Molecular Polarity
Polar Molecules Dipole moments are asymmetrical and don’t cancel . H2O H O net dipole moment Courtesy Christy Johannesson

5 Determining Molecular Polarity
Therefore, polar molecules have... asymmetrical shape (lone pairs) or asymmetrical atoms CHCl3 H Cl net dipole moment Courtesy Christy Johannesson

6 Dipole Moment Nonpolar Polar C O O O H H .. Bond dipoles
In H2O the bond dipoles are also equal in magnitude but do not exactly oppose each other. The molecule has a nonzero overall dipole moment. C O O .. Overall dipole moment = 0 O Bond dipoles Nonpolar H H The overall dipole moment of a molecule is the sum of its bond dipoles. In CO2 the bond dipoles are equal in magnitude but exactly opposite each other. The overall dipole moment is zero. Overall dipole moment Dipole moment, m Polar Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 315

7 Determining Molecular Polarity
Ammonia, NH3

8 Methane and Chloro-methane

9 Carbon dioxide and sulfur dioxide

10 Polar Bonds .. .. .. F O N H Cl H H H B H H F F Polar Polar Nonpolar
Students often confuse electron-domain geometry with molecular geometry. You must stress that the molecular geometry is a consequence of the electron domain geometry. The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them. F F F Cl H Xe C C Cl F F Cl H F F Cl H Polar Nonpolar Nonpolar Polar A molecule has a zero dipole moment because their dipoles cancel one another.