Hi everyone and welcome back to HighSchoolScience101!
Today I'm going to show you a very basic demonstration illustrating the particle model,
and the particle model is important in science because it helps us to explain the characteristics
of solids, liquids and gases, and helps us to explain the processes of moving from a solid
to a liquid to a gas, and back again. The particle model has three main assumptions.
Firstly, that everything around us - solids, liquids and gases - are made up of these tiny
microscopic particles, and I've magnified them here just so you can sort of see what's going on.
Secondly, it assumes that these particles - even in a fixed position like this
in a solid - are constantly moving, so they're constantly vibrating on the spot.
And thirdly, it assumes that these particles are attracted to each other.
Just like opposite ends of magnets, they're attracted to each other and that's really
important to consider when we talk about some of the processes we're going to talk about today.
Let's start off with the solid. In a solid, we say that it has a fixed shape because
the particles are really closely packed into each other and they can't move around freely.
We also say that solids are "incompressible", which means that we can't squish it because
there's no space between the particles for them to move. We also have to remember that in a solid,
the particles are vibrating on the spot. They can't move around much, but they are vibrating
and they are slightly bumping into the particles around them. If we add heat, basically in science
adding heat is the same as adding energy, so if we're adding heat to these particles we're adding
energy to them and they'll start to move around more and start to bump into each other a lot more,
and they'll actually start to break away from each other. Most of them will still stay attached,
but it sort of forms this loose chain where some of them are attached and some of them aren't,
and we call this process "melting". The solid is melting into a liquid
just the same way as when you light a candle, the wax goes from a solid to a liquid.
This is what's happening in the particle model. If we continue to heat up this liquid,
basically these particles are gaining so much energy and they're moving around so much that
they actually start to break free from the rest of the liquid and they form gas particles,
where they're free from each other. Now, these particles will fly in a straight line until they
either hit the container or they hit each other, and then they'll deflect off and go
somewhere else. Because of this we say that gases fill their container, or in this case,
because there's no lid some of them will actually start to leave the container. They'll fly in a
straight line and they'll be leaving the container and forming a vapour, so we call this process
"evaporation". So, we've heated up our liquid and it's formed a gas. Let's say we take away
the heat now, and as I said before if we're adding heat we're adding energy. If we're removing heat,
we're actually removing energy and, as I said at the very start, these particles are attracted to
each other so if we're removing energy they start to move around a bit slower and if they
bump into each other that gives them a chance to stick to each other and actually start to form
droplets when they stick to each other. We call this process "condensation". As these particles
continue to cool down they form a bigger volume of water and they actually form a liquid again.
And if we continue to cool this down - if we put it in the freezer or something - they
actually start to form back into a solid because they're losing so much energy
that they're starting to get strongly attracted to each other and they're starting to freeze together
into a fixed position. We say this process is "freezing" or "solidification", which means
forming a solid. There are two other processes that you might hear about. In "sublimation",
that's when you have a solid that turns into a gas straight away - so it skips the melting point.
An example of this is when you've got a block of dry ice, which is basically solid carbon dioxide,
and it evaporates into a smoky kind of vapour at room temperature, which is why it's sometimes used
for fog machines. So it skips the melting into a liquid stage. The opposite of that
is "deposition", which is when a gas forms a solid straight away - it skips the condensation phase-
and an example of that is frost. Basically that's when you've got water
that's in that cold air that it freezes into a solid straight away,
so it skips the condensation phase and freezes into a solid which is a special type of ice,
in that example, called 'frost'. And that brings us to the end of this lesson.
We've discussed the assumptions of the particle model, we've discussed characteristics of solids,
liquids and gases and what they look like using this model, and we've also discussed some of the
processes of moving from a solid to a liquid to a gas and back again using the particle model.
I hope you enjoyed it, please like, subscribe and leave a comment, and I'll see you next time!