 intermolecular forces. So intermolecular forces are the forces between molecules, and they hold molecules together. So if we have a solid ice cube here, it's at or below zero degrees. So if we give it a little bit more heat energy, while the temperature won't necessarily increase, the ice cube will start to melt. This is a phase change between solid and liquid, and this is at zero degrees Celsius. Now let's increase the temperature a little bit. We've got a liquid. So these molecules are sort of bouncing around. Some have enough energy to escape into the gas phase, but not all of them do. If we give it more heat energy, the molecules move around faster. So let's put a lid on it so they don't all escape, because we're increasing the temperature to 100 degrees Celsius. So more and more of these molecules will have enough energy to escape into the gas phase. So this is a phase change between liquid to gas, and this process is called boiling. So let's look at a singular water molecule. The hydrogens and the oxygen are covalently bonded within the molecule. And unlike over here where we have intermolecular forces, which are the forces between molecules, these three parts over here are covalently bonded. So if we want to separate them into its three individual atoms, we have to break this bond, and this requires an incredible amount of heat energy, and will take us up to 3000 degrees Celsius. So from this, we can determine that intermolecular forces are much weaker than covalent bonds. And in fact, intermolecular forces are much weaker than any internal bond within a molecule.