- [Instructor] In this video
we're gonna familiarize ourselves with matter.
We're gonna thinking about what matters about matter
but in particular, we're gonna think about a lot of words
you'll hear, especially in a chemistry class
and how they might relate to each other
when we're classifying matter.
So first let's start with a definition of matter.
Well, a good definition is anything that has mass
and anything that has volume
where it takes up three-dimensional space is matter
and it has to do both of these things.
Mass, you probably have an intuitive sense.
An elephant has more mass than a mouse.
If we wanna get a little more technical
it's related to how hard it is to accelerate something.
Now you might be saying,
"Isn't this everything that has mass and volume?"
But we have to remind ourselves
even within scientific circles,
there's many things we talk about
that don't have both mass and volume.
For example, we can think about waves.
We could think about energy.
And then you can think about things that have energy
or that have wave-like properties like light or sound.
And all of these things would not be considered matter.
And of course, I guess you could even broaden it to ideas
like love that also would not be matter
but I'm probably going on a bit of a tangent there
but we're gonna stay focused on the matter side
not on the not matter.
And the first division of matter is between
what we could view as pure substances and mixtures.
Now a pure substance, one way to think about it is
no matter how small we get any sample we take
and we don't chemically alter that sample,
so we're not doing any chemistry making
or breaking bonds here.
If we take a chunk of it
you're gonna have consistent chemical properties.
You're going to get the same thing.
Once again, assuming
that you're not changing the structure chemically,
you're not making or breaking chemical bonds,
you can get down to the microscopic
to even the molecular level
and you're going to have the same properties.
While in a mixture that isn't true.
That if you get close enough
you're gonna get chunks of things
that have different properties.
Now within pure substances and I'll give a little bit
of a division within mixtures as well.
Pure substances can be further subdivided.
So here we could have a pure element.
So this is a pure substance
that only has one type of element in it.
And this is an example of pure gold.
And in reality
it's hard to have an absolute 100% pure thing
but most of these gold bars as you see here
you're gonna get a gold atom there.
If you zoom in enough, it is pure gold.
It is a pure element.
Well, what we have over here, this is pure water.
Now water is still a pure substance
because you go down all the way to the smallest level,
to a molecular level.
As long as you are not chemically altering the water
you are going to still get the same thing at any scale.
But water is made up of different types of elements.
The chemical formula for water,
every water molecule has two hydrogens and one oxygen.
And so when you have a pure substance
that has more than one type of element in its smallest unit
that has its chemical properties we call that a compound.
Now I also use this word molecule
when I talked about a water molecule
and sometimes it's confusing.
When do you use compound?
When do you use molecule?
And one way to think about it is a molecule is anything
that has more than one atom bound together.
While a compound is a subset of molecules
that it has different types of atoms bound together.
So for example, if we're thinking about molecules
I'm drawing a little bit of a a little Venn diagram here,
or a set diagram, I should say.
Examples of molecules could be molecular hydrogen.
It has to have the same atom
but they are bonded to each other.
And so actually, if you had a bunch of H2,
molecular hydrogen, that would be a pure element.
It could be O2 molecular oxygen, that is a molecule.
But if we're thinking about compounds,
we could think about H2O.
That is both a molecule and a compound.
All compounds are molecules
but not all the molecules are compounds.
If we think about carbon dioxide, that is a compound.
It has not only more than one atom
but the atoms are of different types.
And of course you can have pure substances
that are neither molecules nor compounds.
You could have a situation like neon, which is a noble gas
and it doesn't like to bond with anything even itself.
And so it could just be a free atom.
So if you had a bunch of neon together
that could be a pure element
that is neither a molecule nor a compound.
Now let's go on the other side of this little taxonomy
that we're creating to mixture.
So mixture, if a pure substance, at any scale
you get down a microscopic scale
and as long as you're not chemically altering
making and breaking bonds,
you're going to get the same properties.
You're going to get the same stuff.
But in a mixture, when you get down to a small scale
you don't necessarily get the same thing
and that you can actually get different things
not by doing chemical changes
but by doing physical changes to them.
So this right over here
where you can clearly see the difference.
So there, it looks like in this rock here
part of it is this one type of glassy looking mineral here
and then you have this other type of mineral looking here.
It's clear that these minerals are mixed together.
And a mixture where it's clear
that the different parts are different stuff
we would call this a heterogeneous mixture, heterogeneous.
Each of these minerals are oftentimes pure substances
but you have a bunch of pure substances mixed together,
but it's pretty easy to pick out where one is
versus the other.
And they aren't mixed together in a uniform way.
And so that's why we call it a heterogeneous mixture.
Now, in this picture on the right
we have to have two mixtures going on.
We have the air up here and air itself is a mixture.
A lot of you might say, "Wait, air is matter.
It doesn't feel like anything is there."
Well that's just 'cause you're used to it.
Matter is anything with mass or volume
and air especially the air molecules for sure have mass
and for sure take up space, they have volume to it.
Matter can come as a gas, as a liquid, as a solid
and even as plasma,
those are states of matter, but that is all matter.
But the reason why the air that we breathe
is 'cause considered a mixture
is that it's full of nitrogen, it's full of oxygen.
It's full of carbon dioxide.
In fact, it's mostly nitrogen and oxygen.
Those things can be physically separated from itself.
You can zoom in on the air
and you can do things to just pick out a nitrogen molecule
or an oxygen molecule or a carbon dioxide molecule
without making or breaking bonds.
But air where you have these different pure substances
that are mixed together really well in a uniform way,
this is known as a homogeneous mixture, homogeneous
and similarly water that you might see in say the ocean
is also gonna be a homogeneous mixture
because it doesn't just have H2O in it.
It for sure is gonna have H2O in it
but it's also going to have sodium chloride
that is been dissolved in it.
So it'll have sodium ions and chloride anions in it.
It's gonna probably have other things
that are mixed into it.
It's probably gonna have molecular oxygen mixed into it
but it's mixed generally pretty uniformly.
So that's why we call it a homogeneous mixture.
So I'll let you go there.
This is giving you the toolkit for a lot of the words
that you will hear in chemistry class.
And it's useful to be able to know
what these different things mean.