0:05 in today's video we're going to look at
0:07 the three states of matter
0:09 solid liquid and gas
0:11 and see how substances can change from
0:14 one state to another
0:16 to do this we're going to use a model
0:18 called particle theory which helps us
0:20 explain how the particles in each state
0:22 behave by considering each particle as a
0:29 in solids there are strong forces of
0:31 attraction between the particles
0:33 which holds them all close together in a
0:35 fixed position
0:38 to form a regular lattice structure
0:40 and because the particles are fixed the
0:42 overall substance keeps a definite shape
0:45 and volume so you can't flow like a liquid
0:47 liquid
0:48 the particles can vibrate in their
0:50 position though
0:51 so you can imagine them constantly
0:54 jostling against each other
0:57 now if we heat up a solid its particles
1:00 gain more energy and start to vibrate
1:01 even more
1:04 which weakens the forces between them
1:05 and at a certain temperature which we
1:07 call the melting point the particles
1:09 have enough energy to break free of
1:11 their bonds and the solid melts into a liquid
1:14 liquid
1:16 in liquids there are only weak forces of
1:18 attraction between the particles
1:20 so they're free to move around and are
1:22 arranged pretty randomly
1:24 however the weak forces of attraction do
1:25 mean that the particles tend to stick
1:28 together and are fairly compact
1:30 this means that liquids have a definite volume
1:31 volume
1:34 even though the overall shape can change
1:40 if we then heat up our liquid the
1:43 particles will gain more energy
1:44 and this will make the particles move
1:46 around faster
1:48 which weakens the forces holding the
1:50 particles together
1:52 and once we reach the boiling point the
1:54 particles will have enough energy to
1:56 break the bonds altogether
1:58 and so the liquid boils or evaporates
2:03 in gases the force of attraction between
2:05 the different particles is very weak
2:07 so they're basically free to move around
2:09 by themselves
2:11 this means that gases don't keep a
2:14 definite shape or volume and instead
2:15 will always fill a container as they
2:18 spread out as much as possible
2:20 we normally say that gases are
2:23 constantly moving with a random motion
2:25 and this can be a bit confusing because
2:27 gas particles actually move in straight
2:30 lines they don't randomly swerve
2:32 what we actually mean by random motion
2:34 is that particles can travel in any
2:36 direction and they'll end up being
2:38 deflected by solid walls or other gas
2:44 when we heat up a gas and the particles
2:46 all get more energy and so travel faster
2:49 the gas will either expand if the
2:51 container it's in is expandable like a balloon
2:52 balloon
2:54 or if the container is fixed then the
2:59 on the other hand if we cool the gas
3:01 down enough then the particles won't
3:03 have enough energy to overcome the
3:05 forces of attraction between them
3:07 and so bonds will start to form between
3:08 the particles
3:15 then as we call the liquid even further
3:17 the same thing happens
3:19 the particles won't have enough energy
3:22 to overcome the attraction between them
3:25 and this time even more bonds form
3:27 fixing the particles in place and
3:34 now the last thing we need to mention is
3:35 that the particle model we used for
3:37 explaining the states of mata isn't perfect
3:39 perfect
3:41 in reality particles aren't actually
3:44 solid inelastic or spheres
3:49 instead they're atoms ions or molecules
3:51 another issue is that the model doesn't
3:53 include any details of the forces
3:55 between the particles
3:57 for example it doesn't consider how
3:58 strong they are or how many of them
4:00 there are
4:02 that said models like this are still a
4:04 useful simplification that allow us to
4:12 anyway that's all for today so if you
4:14 enjoyed it then please share with your
