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When you have strong intermolecular attractive forces you need high amount of energy to break the attraction forces. Since energy is proportional to the temperature, higher the energy provided the higher will be the temperature needed to break the bond. @taramgrant0543664 I actually have no idea how to explain this. any idea ? This what I can explain. But I have that unsatisfactory feeling about this answer! @Photon336 @sweetburger
In the process of converting a liquid to a gas (i.e. boiling), we are providing sufficient energy to the molecules so that they can overcome the intermolecular forces present between them and exist as 'free' molecules in the gaseous phase (i.e. no intermolecular interactions). Whilst the molecules in a liquid have some movement in that they can slide past one another, it is these forces which give a liquid its fixed volume and prevent this completley 'free' movement. In each of three types of intermolecular forces that may be present (Hydrogen Bonding, Dipole-Dipole Interactions and van der Wall's Intermolecular Forces), the stronger the electrostatic interactions (i.e. the interaction between the positive and negative ends of molecules), the stronger the forces in question and thus the greater the level of attraction between the molecules. These interactions/bonds are constantly being broken/formed as the molecules move by one another So, if we imagine a huge network of molecules almost 'linked' together as they move by one another, we need to provide more energy (in the form of heat) to get to a point where they can all roam about freely with respect to one another in substances where they are strongest. Based on this reasoning, liquids with strong (or many) intermolecular interactions will have a higher boiling point than those with weaker degrees of interactions. I haven't touched on what's actually happening in these intermolecular forces here (i.e. what's happening in a Hydrogen Bond, etc.), but hopefully this should be enough to able to pick through and form a short 3-4 sentence answer to your question....and hopefully you can understand it also! Have you met the different types of intermolecular bonds/forces before @robijo7698 ?
@Ciarán95 explained it perfectly