[Music] hi welcome back to three times I think a UK by the end of this video you should be able to draw diagrams to model the differences in the arrangement of particles between solids liquids and gases you should then be able to calculate the density of material and finally you should be able to explain the differences in density between different states of matter now there are three common states of matter and these are solids liquids and gases we're going to start by looking at how the particles are arranged in these three states let's start with solids I'm showing the arrangement of particles in a solid here in a solid the particles are very close together and they're arranged in a regular pattern particles in a solid vibrate but they do not move from place to place here's the arrangement of particles in a liquid in a liquid the particles are still close together but they're not arranged in a regular pattern in fact the particles in the liquid can move around each other this shows the arrangement of particles in the gas you can see that the particles are very far apart and they're not arranged in any pattern in a gas the particles are moving very rapidly now in the examiner could be asked to draw the arrangement of particles in solids liquids and gases so it's really important that you learn them okay we're going to take a look now at density the density of material tells us the mass for a given volume now that sounds tricky but the idea is relatively straightforward I'm showing you here a brick under polystyrene block the brick has a high density it has lots of mass packed into its volume the polystyrene block has a low density but because it's got a lower mass packed into its volume we can calculate density using this equation the density equals the mass and kilograms divided by the volume in meters cubed the unit of density is kilograms per meter cubed and here's a triangle if you prefer to use these now you're not given this equation in the exam so it's important that you learn it here's a question for you to try a block of wood has a mass of 150 kilograms under volume of Nohr point 3 meters cubed calculate the density pause the video and try this yourself okay so the density equals the mass divided by the volume the mass is 150 kilograms under volume has no point three meters cubed putting these into the equation it is a density of 500 kilograms per meter cubed now we can use the particle model that we saw earlier to explain the density of different materials solids usually have a very high density because the particles are part closely together solid have a lot of mass for their volume liquids also usually have a high density again because the particles are close together liquids have a lot of mass for their volume now gases have a low density but because the particles are very far apart so gases only have a small mass for their volume now there are some exceptions these rules for example polystyrene which we saw earlier this is a solid but it has a low density that because of the very open structure Una's fill of air spaces so it has a smaller mass fluid volume I'm showing you polystyrene under a microscope here and you can see the air spaces remember that you'll find plenty of questions on density in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to draw diagrams to model the differences in the arrangement of particles between solids liquids and gases you should then be able to calculate the density of material and finally you should be able to explain the differences in density between different states of matter [Music]