GCSE Chemistry - States of Matter & Changing State #21

This video explains 'particle theory' and uses it to describe the 3 states of matter: solid, liquid and gas. It also covers how substances move between these states at the particle level.

This video is suitable for:
- All exam boards
- Triple and combined science
- Higher and Foundation tiers

The last part of the video on the limitations of particle theory is only relevant to higher tier students, but this is labelled with the usual "Higher Tier" box in the top left corner.

[Cognitoedu]

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Amadeus & Tom

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[frs]

particle theory helps us
explain how the party was 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 where
it 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 can't flow like a liquid
the particles can vibrate in their
position though so if you imagine them
constantly adjusting 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
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 the 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
you mean that the particles tend to
stick together and a 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 heats 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 of every week
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 had 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 travels
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 weren'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 were used for
explaining the states of matter isn't
perfect.
in reality particles aren't actually
solid in elastic or spheres instead
their 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 theirs are still a
useful simplification that allow us to
understand a complicated concept.

[Latitevo_official]

• Solids: Particles have strong attractions and are tightly packed in a fixed structure. Heating increases vibrations until they break free at the melting point.
• Liquids: Particles have weaker attractions and can move around. Heating increases particle movement until they break free at boiling point.
• Gases: Particles have very weak attractions and move freely. Heating increases particle speed, causing expansion or increased pressure. Cooling can condense gas into a liquid and further cooling freezes it into a solid.

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