- [Instructor] What we have depicted here
in these four images are matter
in different states.
And we're using what's known as a particulate model.
And these are two dimensional particulate models
which are simple ways of imagining
what is going on at a molecular scale
inside of matter.
And so you can imagine each of these circles to,
depending on what we're dealing with,
it's either an ion,
it's a molecule,
or it's an atom.
But it's telling us how these molecules
or ions or atoms are interacting with each other.
Which determine what state of matter we are in.
So pause this video and think about
which of these quadrants represent matter
in a solid state,
which represent matter in a liquid state,
and which represents matter in a gas state.
All right, so there's a few that might have been
somewhat obvious to you.
If you imagine each of these circles to be an ion,
you could imagine these to be ionic solids
that we've seen.
That type of lattice structure.
If you imagine each of these circles
to be atoms that are forming covalent bonds
with neighboring circles,
then you could imagine this being
a covalent network solid.
If you imagine each of these circles are molecules,
and due to intermolecular forces,
they have arranged in this regular way
to the other molecules,
then you could imagine this is a molecular solid.
You could also imagine that each of these
are metal atoms and they're all sharing
the soup of valance electrons.
And so we're dealing with a metallic solid.
But no matter which visualization you use
or what you're imagining this to be,
it's pretty clear that this is a solid.
And one of the major giveaways of that
is that it's not taking the shape of the container.
These molecules, I guess you could say these particles,
aren't able to fully slide past each other
and take the shape of the container
that they're in,
which would happen in a liquid.
And they're clearly not able to overcome
the forces between the particles
to then go off and do their own thing,
which we would see in a gas
and bounce around the entire container.
So this is clearly a solid.
Now this one on the bottom left,
here it does look like the particles
are taking the shape of the container.
They are able to slide past each other,
but there are still intermolecular forces there
that keep them from flying apart.
So this is clearly a liquid.
And in this bottom right quadrant,
you could imagine what's going on.
These particles, whether they're molecules or ions,
they have for the most part
been able to overcome the intermolecular forces
between them.
And so they are just bouncing around,
fully taking the form of the container
that they are in.
And so this is a gas.
Now what about this right over here?
It looks kind of like a solid
in that it's not taking the shape
of its container.
But it's also irregular,
the way that you might expect a liquid to be,
at least at a snapshot in time.
And this, because it's not taking the shape
of its container,
and because these molecules or these particles,
even though they are irregular,
they aren't sliding past each other
like you would expect in a liquid.
This too is a solid,
but we call this an amorphous solid.
It does not have this nice crystalline structure
like we've seen with the crystalline solids.
And there's a lot of examples
of amorphous solids.
Most of the solids you know in your life
that are stretchy,
that have an elastic quality to them,
are amorphous solids.
For example, if you had a little bunch of natural rubber,
you could pull on it and it might look
something like this when you stretch it.
But then when you let go,
it will go back to its original state
or maybe close to its original state.
And the reason why it does that
is natural rubber is made up of polymers.
And just to imagine what a polymer is,
this is a molecular structure
of actual natural rubber.
It's a chain of carbons that are bonded to hydrogens.
And if you imagine it,
if you were to zoom out from this,
you imagine these chains,
these very long chains of carbons
with hydrogens.
And then in natural rubber,
they all get tangled up with each other.
And so they're forming this amorphous solid.
It doesn't look exactly like this particulate model
we just saw,
it's more just imagine a bunch of strings
that are all tangled up.
And so if you were to pull on them,
they are able to stretch,
but then you let go,
they get back to close to where they were before.
Now rubber isn't the only polymer.
For example, the plastics you see all around you
are also polymers.
And a few are mostly amorphous.
And then a few are mostly crystalline.
And a lot are what we would call semi-crystalline.
Which means they have both amorphous
and crystalline regions.