Presentation on theme: "Molecular Polarity Notes"— Presentation transcript:
1 Molecular Polarity Notes Which Molecules Have Dipole Moments?Any two atom molecule (diatomic) with a polar bond.With three or more atoms (polyatomic) there are two considerations.There must be a polar bond. (H2O & NH3)Geometry can’t cancel it out.
2 Dipole MomentsA molecule with a center of negative charge and a center of positive charge is dipolar (two poles), or has a dipole moment.Center of charge doesn’t have to be on an atom.Will line up in the presence of an electric field.
3 When no electric field is present, the molecules are randomly oriented When no electric field is present, the molecules are randomly oriented. When the field is turned on, the molecules tend to line up with their negative ends toward the positive pole and their positive ends toward the negative pole.
4 C. Bond Polarity and Dipole Moments A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge
5 How It is drawnH - Fd+d-The dipolar character of a molecule is often represented by an arrow pointing to the negative charge center with the tail of the arrow indicating the positive center of charge
6 + - A. Dipole Moment H Cl Direction of the polar bond in a molecule. Arrow points toward the more e-neg atom.H Cl+-
7 B. Determining Molecular Polarity Depends on:dipole momentsmolecular shape
8 B. Determining Molecular Polarity Nonpolar MoleculesDipole moments are symmetrical and cancel out.BF3FB
9 B. Determining Molecular Polarity Polar MoleculesDipole moments are asymmetrical and don’t cancel .H2OHOnetdipolemoment
11 C. Bond Polarity and Dipole Moments Water molecule dipole moment
12 C. Bond Polarity and Dipole Moments The polarity of water affects its propertiesPermits ionic compounds to dissolve in itCauses water to remain liquid at higher temperature
13 Some Molecules Have Polar Bonds, but Do Not Have Dipole Moment. This occurs when the individual bond polariteis are arranged in such a way that they cancel each other out.EX: CO2 molecule (oppose bond polarities cancel out)
14 Geometry and polarity Three shapes will cancel them out. Planar triangles120º
15 Geometry and polarityThree shapes will cancel them out.Tetrahedral