Intermolecular Forces Forces of attraction between molecules – Intermolecular forces create attractions that hold molecules close to each other in the formation of liquids and solids. The higher the intermolecular forces between the molecules; the higher the melting and boiling point of a substance. 3 types of Intermolecular Forces: Dipole-Dipole Forces Hydrogen Bonds London Dispersion Forces Intermolecular forces are related to the electronegativity differences (polarity) of the bonds and the molecular shape. Let’s take a very simple linear molecule with a high polarity BrF. – F = 3.98 Br = 2.96 Difference = 1.02 The bond is polar covalent. This creates a dipole. Dipole but opposite charges separated by a short distance. – We indicate the direction of a dipole by an arrow with its head pointing toward the negative side of the molecule. Dipole Arrow: Dipoles act as miniature magnets attraction each other’s opposite poles. The attraction created is called a dipole-dipole force and has the affect of holding molecules near each other raising the melting and boiling points. Slide 1: Coordinate crystal of BrF Dipole Dipole Force of attraction between polar molecules. – –
Intermolecular Forces – Forces of attraction between molecules Intermolecular forces create attractions that hold molecules close to each other in the formation of liquids and solids. The higher the intermolecular forces between the molecules; the higher the melting and boiling point of a substance. 3 types of Intermolecular Forces: Dipole-Dipole Forces Hydrogen Bonds London Dispersion Forces Intermolecular forces are related to the electronegativity differences (polarity) of the bonds and the molecular shape. Let’s take a very simple linear molecule with a high polarity – BrF. F = 3.98 Br = 2.96 Difference = 1.02 The bond is polar covalent. This creates a dipole. Dipole – but opposite charges separated by a short distance. We indicate the direction of a dipole by an arrow with its head pointing toward the negative side of the molecule. Dipole Arrow: Dipoles act as miniature magnets attraction each other’s opposite poles. The attraction created is called a dipole-dipole force and has the affect of holding molecules near each other raising the melting and boiling points. Slide 1: Coordinate crystal of BrF Dipole – Dipole – Force of attraction between polar molecules.
Intermolecular%20Forces.docx