Intermolecular forces are the attraction and repulsion forces that exist between molecules. Intermolecular forces are much weaker than intramolecular forces such as covalent and ionic bonds. Intramolecular forces are what determine whether a substance will be a gas, liquid or solid at room temperature. The greater the intermolecular forces exhibited by a compound the higher its boiling point and melting point as it takes more energy to overcome its intermolecular forces. Intermolecular forces are sometimes referred to collectively as Van der Waals forces but the term Van der Waals forces should not be used to refer to hydrogen bonds. There are 4 main categories of intermolecular forces: London dispersion forces, dipole-dipole attractions, ion-dipole attractions and hydrogen bonds with dispersion forces being the weakest and hydrogen bonds being the strongest.