We humans have known for thousands of years,
just looking at our environment around us,
that there're different substances.
These different substances...tend to have different properties.
Not only do they have different properties;
one might reflects light in a certain way, or not reflect light.
Or be a certain color, or be have a certain temperature;
be liquid, or gas or be a solid.
But we also start to observe
how they react with each other in certain circumstances.
and here's pictures of some of these substances.
This right here is carbon, and this is in the...in its graphite form
This right here is lead; this right here is gold
and all of the ones that I've drawn, that I've shown pictures of here,
I got them all from this website right over there
All of these are in their solid form, but we also know that we...
It looks like there's certain types of air in it,
certain types of air particles,
and depending on what type of air particles you're looking at
whether it is carbon, or oxygen, or nitrogen,
that seems to have different types of properties.
Or, there are some other things that can be liquid,
or even if you raise the temperature high enough on these things.
If you raise the temperature high enough on gold or lead,
you could get a liquid.
Or if you kind of -- if you burn this carbon,
you can get it to a gaseous state,
you can release it into the atmosphere,
you can break its structure.
So these are things that we've all kind of
that humanity has observed for thousands of years.
But that leads to a natural question
that used to be a philosophical question,
but now we can answer it a little bit better,
and that question is, if you keep breaking down this carbon
into smaller and smaller chunks,
if there's some smallest chunk,
some smallest unit of this stuff, of this substance
that still has the properties of carbon?
And if you were to somehow break that down even further,
you would lose the properties of the carbon?
And the answer is: there is.
And so just to get our terminology,
we call these different substances, that these pure substances
that have these specific properties at certain temperatures,
and react in certain ways,
we call them elements.
Carbon is an element. Lead is an element. Gold is an element.
You might say that water is an element.
And in history, people have referred to water as an element.
But now we know that water is made up of more basic elements.
It's made of oxygen and of hydrogen.
And all of our elements are listed here
in the periodic table of elements.
C stands for carbon
-- I'm just going through the ones
that are very relevant to humanity --
but over time you'll probably familiarize yourself with all of these.
This is oxygen. This is nitrogen. This is silicon.
This is -- Au is gold. This is lead.
And that most basic unit of any of these elements is the atom.
So if you were to keep digging in
and keep taking smaller and smaller chunks of this.
Eventually you would get to a carbon atom.
Do the same thing over here,
eventually you'd get to a gold atom.
You did the same thing over here,
eventually you'd get some of this little small
-- for a lack of a better word -- particle,
that you'd call a lead atom.
And you wouldn't be able to break that down anymore
and still call that lead,
for it still have the properties of lead.
And just to give you an idea
-- this is really something that I have trouble imagining --
is that atoms are unbelievably small.
Really, unimaginably small.
So for example, carbon.
My hair is also made out of carbon.
In fact most of me is made out of carbon.
In fact most of all living things are made out of carbon.
And so if you took my hair. And so my hair is carbon.
My hair is mostly carbon.
So if you took my hair right over here
-- my hair isn't yellow
but it contrasts nicely with the black.
My hair is black. But if I did that,
you wouldn't be able to see it on the screen.
But if you took my hair here, I would have asked you
how many carbon atoms wide is my hair?
So if you took a cross-section of my hair, not the length,
the width of my hair, and said:
how many carbon atoms wide is that?
And you might guess, oh, Sal already told me, it's very small,
so maybe there's a thousand carbon atoms there,
or ten thousand, or a hundred thousands,
and I would say, no!
There are one million carbon atoms.
Or you could string one million carbon atoms
across the width of the average human hair.
And that's obviously an approximation,
it's not exactly one million,
but that gives you a sense of how small an atom is.
You know, pluck a hair out of your head
and just imagine putting a million things
next to each other across the hair,
not the length of the hair, the width of the hair.
It's even hard to see the width of hair.
And there would be a million carbon atoms
just going along it.
Now it would be pretty cool in and of itself
-- we do know that
there is this most basic building block of carbon,
this most basic building block of any element.
But what's even neater is that
those basic building blocks are related to each other.
A carbon atom is made of even more fundamental particles.
A gold atom is made up of even more fundamental particles.
And they are actually defined by
the arrangement of those fundamental particles.
And if you were to change
the number of fundamental particles you have.
You could change the properties of that element,
how it would react,
or you could even change the element itself.
And just to understand it a little bit better.
Let's talk about those fundamental elements.
So you have the proton.
And the proton is actually the defining
-- the number of protons in the nucleus of an atom
and I'll talk about the nucleus in a second --
that is what defines the element.
So this is what defines an element.
When you look at the periodic table right here,
they are actually written in order of atomic number,
and the atomic number is
literally just the number of protons in the element.
So by definition, hydrogen has 1 proton.
Helium has 2 protons. Carbon has 6 protons.
You cannot have carbon with 7 protons.
If you did, it would be nitrogen,
It would not be carbon anymore.
Oxygen has 8 protons.
If somehow you were to add another proton to there,
it wouldn't be oxygen anymore.
It would be fluorine. So it defines the element.
It defines the element.
And the atomic number, the number of protons,
the number of protons -- and remember,
that's the number that's written right at the top here
for each of these elements in the periodic table
-- the number of protons
is equal to the atomic number.
Is equal to the atomic number.
And they put that number up here because that is
the defining characteristic of an element.
The other two constituents of an atom
-- I guess we could call it that way --
are the electron and the neutron.
And the model you can start to build in your head
-- and this model, as we go through chemistry we'll see,
it will get a little bit more abstract
and really hard to conceptualize --
but one way to think about it is
you have the protons and the neutrons
that are the center of the atom.
They are the nucleus of the atom.
So for example, carbon, we know, has 6 protons.
So one, two, three, four, five, six.
Carbon 12, which is a version of carbon,
will also have 6 neutrons.
You can have versions of carbon
that have a different number of neutrons.
So the neutrons can change, the electrons can change,
you can still have the same element.
The protons can't change.
You change the protons, you got a different element.
So let me draw a carbon 12 nucleus.
So one, two, three, four, five, six.
So this right here is the nucleus of carbon 12.
And sometimes it will be written like this.
And sometimes they will actually write
the number of protons as well.
And the reason why we write it carbon 12
-- you know I counted out 6 neutrons --
is that this is the total
you could view this as the total number of
-- one way to view it,
and we'll get a little bit of nuance in the future
-- is that this is the total number
of protons and neutrons inside of its nucleus.
And this carbon by definition has an atomic number of 6,
but we can rewrite it here
just so that we can remind ourselves.
So at the center of the carbon atom we have this nucleus.
And carbon 12 will have 6 protons and 6 neutrons.
Another version of carbon, carbon 14, will still have
6 protons, but then it would have 8 neutrons.
So the number of neutrons can change,
but this is carbon 12 right over here.
And if carbon 12 is neutral --
and I'll give a little nuance on this word in a second as well --
if it's neutral it will also have 6 electrons.
So let me draw those 6 electrons.
One, two, three, four, five, six.
And one way -- and this is maybe the first order way
of thinking about the relationship
between the electrons and the nucleus --
is that you can imagine the electrons
are kind of moving around,
buzzing around this nucleus.
One model is you could kind of
thinking of them as orbiting around the nucleus,
but that's not quite right.
They don't orbit the way that a planet, say,
orbits around the Sun.
But that's a good starting point.
Another way is that they kind of jumping around the nucleus
or they are buzzing around the nucleus.
And that's just because
reality just gets very strange at this level,
and we'll actually have to get to quantum physics
to really understand what the electron is doing.
But a first mental model in your head is
at the center of this atom, of this carbon 12 atom,
you have this nucleus.
You have this nucleus right over there.
And these electrons are jumping around this nucleus.
And the reason why these electrons
don't just go off away from this nucleus,
why they are kind of bound to this nucleus,
and they form part of this atom,
is that protons have a positive charge,
and electrons have a negative charge.
And it's one of these properties of these fundamental particles.
When you start thinking about
what is a charge fundamentally other than a label,
and it starts to get kind of deep.
But the one thing that we know,
when we talk about electro-magnetic force,
is that unlike charges attract each other.
So the best way to think about it is:
protons and electrons,
because they have different charges,
they attract each other.
Neutrons are neutral,
so they're really just sitting here inside of the nucleus,
and they do affect the properties on some level,
for some atoms of certain elements.
But the reason why we have the electrons
not just flying off on their own
is because they are attracted.
They are attracted towards the nucleus.
And they also have an unbelievably high velocity
-- it's actually hard for --
we start touching once again
on a very strange part of physics
once we start talking about
what an electron actually is doing
-- but is has enough --
I guess you could say
it's jumping around enough
that it doesn't want to just fall into the nucleus,
I guess is one way of thinking about it.
And so, I mentioned carbon 12 right over here
defined by the number or protons.
Oxygen would be defined by having 8 protons.
But once again, electrons can interact with other electrons.
They can be taken away by other atoms.
And that actually forms
a lot of our understanding of chemistry.
It's based on how many electrons an atom has,
or a certain element has.
And how those electrons are configured,
and how the electrons of other elements are configured,
or maybe other atoms of that same element.
We can start to predict how an atom of one element
can react with another atom of that same element,
or an atom of one element -- how it could react,
or how it could bond, or not bond, or be attracted to,
or repel another atom of another element.
So for example,
and we'll learn a lot more about this in the future,
is: it is possible for another atom some place
to swipe away an electron from a carbon,
just because for whatever reason --
and we'll talk about certain neutral atoms of certain elements
have a larger affinity for electrons than others.
So one, maybe one of those,
swipes an electron away from a carbon,
and then this carbon will be
having less electrons than protons,
so then we'll have 5 electrons and 6 protons.
And then we'd have a net positive charge.
So in this carbon 12, the first version I did,
I had 6 protons, 6 electrons, the charges canceled out.
If I lose an electron, then I only have 5 of these,
and then I would have a net positive charge.
And we're going to talk a lot more
about all of this throughout the chemistry playlist,
but hopefully you have an appreciation that
this is already starting to get really cool.
We can already get to this fundamental building block
called the atom.
And what's even neater is that
this fundamental building block is built of
even more fundamental building blocks.
And these things can all be swapped around
to change the properties of an atom,
or even go from an atom of one element
to an atom of another element.