in today's video we're going to look at the three states of matter solid liquid and gas and see how substances can change from one state to another to do this we're going to use a model called particle theory which helps us explain how the particles in each state behave by considering each particle as a small solid inelastic sphere in solids there are strong forces of attraction between the particles which holds them all close together in a fixed position to form a regular lattice structure and because the particles are fixed the overall substance keeps a definite shape and volume so you can't flow like a liquid the particles can vibrate in their position though so you can imagine them constantly jostling against each other now if we heat up a solid its particles gain more energy and start to vibrate even more which weakens the forces between them and at a certain temperature which we call the melting point the particles have enough energy to break free of their bonds and the solid melts into a liquid in liquids there are only weak forces of attraction between the particles so they're free to move around and are arranged pretty randomly however the weak forces of attraction do mean that the particles tend to stick together and are fairly compact this means that liquids have a definite volume even though the overall shape can change and so flow to fit a container if we then heat up our liquid the particles will gain more energy and this will make the particles move around faster which weakens the forces holding the particles together and once we reach the boiling point the particles will have enough energy to break the bonds altogether and so the liquid boils or evaporates into a gas in gases the force of attraction between the different particles is very weak so they're basically free to move around by themselves this means that gases don't keep a definite shape or volume and instead will always fill a container as they spread out as much as possible we normally say that gases are constantly moving with a random motion and this can be a bit confusing because gas particles actually move in straight lines they don't randomly swerve what we actually mean by random motion is that particles can travel in any direction and they'll end up being deflected by solid walls or other gas particles randomly when we heat up a gas and the particles all get more energy and so travel faster the gas will either expand if the container it's in is expandable like a balloon or if the container is fixed then the pressure will just increase on the other hand if we cool the gas down enough then the particles won't have enough energy to overcome the forces of attraction between them and so bonds will start to form between the particles condensing the gas into a liquid then as we call the liquid even further the same thing happens the particles won't have enough energy to overcome the attraction between them and this time even more bonds form fixing the particles in place and freezing the liquid into a solid now the last thing we need to mention is that the particle model we used for explaining the states of mata isn't perfect in reality particles aren't actually solid inelastic or spheres instead they're atoms ions or molecules another issue is that the model doesn't include any details of the forces between the particles for example it doesn't consider how strong they are or how many of them there are that said models like this are still a useful simplification that allow us to understand a complicated concept anyway that's all for today so if you enjoyed it then please share with your friends and we'll see you next time