Intramolecular Forces These are forces that are “within” the molecule and are the bonds. There can be polar or nonpolar covalent bonds. Ionic bonds do not occur b/w molecules These forces are very strong and hold molecules and compounds together.

Intermolecular Forces These are forces that are “between” the molecules or between ions. These forces are known as van der Waals Forces They can one of two types, London Dispersion or Dipole-Dipole. These forces are very weak compared to the intramolecular forces.

Phases of Matter and Kinetic Molecular Theory In order for a substance to melt (solid to liquid) and boil (liquid to gas) the addition of energy must overcome the attractive forces of attraction between the molecules. The temperature at which a substance will undergo these phase changes depends on the intermolecular forces holding the molecules together.

Phases of Matter and Kinetic Molecular Theory If a substance has low attractive forces, it will have low melting and low boiling points. If a substance has stronger forces, it will have a higher melting and boiling point, because it will take more energy to overcome the forces. In addition to phase changes, intermolecular forces also play a role in compressibility, fluidity, viscosity, surface tension, and capillarity.

London Dispersion Forces London Dispersion Forces are the weakest example of intermolecular forces. They are created by the temporary shifts of electrons in the electron clouds. This force is present in all molecules, but unique because it is the only one that occurs in nonpolar molecules.

Dipole-Dipole Forces These can only be found between polar molecules, and are stronger because the dipoles are not temporary. They are stronger due to the dipoles within the molecule. These dipoles are caused by differences in electonegativities, which will not change and are permanent.

Hydrogen Bonding Hydrogen Bonding is a special type of dipole-dipole interaction. It is created by the polar bond that forms when hydrogen is part of a polar molecule with Fluorine, Oxygen, or Nitrogen. The positively charged hydrogen is attracted to the negatively charged portion of another molecule.

Effects of Hydrogen Bonding The more hydrogen bonding in a substance, the more energy it requires to separate. And the more energy required to separate, the more energy it takes to change states from solid to liquid to gas. AKA Increase the Boiling Point Effects of Hydrogen Bonding