WEBVTT

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We humans have known,
for thousands of years,

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just looking at our
environment around us,

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that there are
different substances.

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And these different
substances tend

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to have different properties.

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And not only do they have
different properties,

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one might reflect
light in a certain way,

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or not reflect light, or
be a certain color, or at

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a certain temperature, be
liquid or gas, or be a solid.

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But we also start
to observe how they

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react with each other in
certain circumstances.

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And here's pictures of
some of these substances.

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This right here is carbon.

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And this is in
its graphite form.

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This right here is lead.

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This right here is gold.

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And all of the ones that I've
shown pictures of, here--

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and I got them all from this
website, right over there--

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all of these are in
their solid form.

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But we also know that
it looks like there's

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certain types of air, and
certain types of air particles.

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And depending on what
type of air particles

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you're looking at, whether it
is carbon or oxygen or nitrogen,

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that seems to have different
types of properties.

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Or there are other things
that can be liquid.

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Or even if you raise the
temperature high enough

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on these things.

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You could, if you raise
the temperature high enough

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on gold or lead, you
could get a liquid.

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Or if you, kind of, if
you burn this carbon,

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you can get it to
a gaseous state.

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You can release it
into the atmosphere.

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You can break its structure.

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So these are things that we've
all, kind of, that humanity

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has observed for
thousands of years.

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But it leads to a
natural question

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that used to be a
philosophical question.

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But now we can answer
it a little bit better.

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And that question is, if you
keep breaking down this carbon,

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into smaller and
smaller chunks, is there

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some smallest chunk, some
smallest unit, of this stuff,

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of this substance, that still
has the properties of carbon?

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And if you were
to, somehow, break

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that even further,
somehow, you would

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lose the properties
of the carbon.

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And the answer is, there is.

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And so just to get
our terminology,

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we call these
different substances--

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these pure substances that
have these specific properties

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at certain
temperatures and react

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in certain ways-- we
call them elements.

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Carbon is an element.

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Lead is an element.

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Gold is an element.

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You might say that
water is an element.

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And in history, people
have referred to water

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as an element.

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But now we know that water is
made up of more basic elements.

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It's made of oxygen
and of hydrogen.

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And all of our elements
are listed here

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in the Periodic
Table of Elements.

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C stands for carbon-- I'm just
going through the ones that

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are very relevant to humanity,
but over time, you'll

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probably familiarize
yourself with all of these.

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This is oxygen.

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This is nitrogen.

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This is silicon.

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Au is gold.

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This is lead.

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And that most basic unit, of any
of these elements, is the atom.

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So if you were to keep
digging in, and keep

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taking smaller and
smaller chunks of this,

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eventually, you would
get to a carbon atom.

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Do the same thing over
here, eventually you

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would get to a gold atom.

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You did the same thing
over here, eventually,

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you would get
some-- this little,

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small, for lack of a
better word, particle,

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that you would call a lead atom.

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And you wouldn't be
able to break that down

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anymore and still
call that lead,

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for it to still have
the properties of lead.

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And just to give you an idea--
this is really something

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that I have trouble
imagining-- is

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that atoms are
unbelievably small, really

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unimaginably small.

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So for example, carbon.

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My hair is also
made out of carbon.

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In fact, most of me
is made out of carbon.

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In fact, most of all living
things are made out of carbon.

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And so if you took my hair--
and so my hair is carbon,

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my hair is mostly carbon.

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So if you took my
hair-- right over here,

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my hair isn't yellow,
but it contrasts nicely

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with the black.

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My hair is black,
but if I did that,

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you wouldn't be able to
see it on the screen.

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But if you took my
hair, here, and I

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were to ask you, how many
carbon atoms wide is my hair?

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So, if you took a cross
section of my hair, not

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the length, the
width of my hair,

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and said, how many carbon
atoms wide is that?

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And you might
guess, oh, you know,

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Sal already told me
they're very small.

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So maybe there's 1,000 carbon
atoms there, or 10,000,

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or 100,000.

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I would say, no.

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There are 1 million
carbon atoms,

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or you could string 1
million carbon atoms

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across the width of
the average human hair.

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That's obviously
an approximation.

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It's not exactly 1 million.

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But that gives you a sense
of how small an atom is.

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You know, pluck a
hair out of your head,

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and just imagine
putting a million things

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next to each other,
across the hair.

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Not the length of the hair,
the width of the hair.

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It's even hard to see
the width of a hair,

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and there would be a
million carbon atoms,

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just going along it.

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Now it would be pretty
cool, in and of itself,

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that we do know that there
is this most basic building

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block of carbon, this most basic
building block of any element.

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But what's even neater is
that, those basic building

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blocks are related
to each other.

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That a carbon atom is made
up of even more fundamental

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particles.

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A gold atom is made up even
more fundamental particles.

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And depending-- and
they're actually

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defined by the arrangement of
those fundamental particles.

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And if you were to change the
number of fundamental particles

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you have, you could change the
properties of the element, how

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it would react, or you could
even change the element itself.

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And just to understand
it a little bit better,

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let's talk about those
fundamental elements.

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So you have the proton.

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And the proton is actually
the defining-- the number

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of protons in the
nucleus of an atom,

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and I'll talk about the
nucleus in a second-- that

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is what defines the element.

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So this is what
defines an element.

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When you look at the
periodic table right here,

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they're actually written
in order of atomic number.

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And the atomic
number is, literally,

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just the number of
protons in the element.

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So by definition,
hydrogen has one proton,

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helium has two protons,
carbon has six protons.

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You cannot have carbon
with seven protons.

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If you did, it
would be nitrogen.

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It would not be carbon anymore.

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Oxygen has eight protons.

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If, somehow, you were to
add another proton to there,

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it wouldn't be oxygen anymore.

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It would be fluorine.

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So it defines the element.

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And the atomic
number, the number

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of protons-- and
remember, that's

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the number that's
written right at the top,

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here, for each of these
elements in the periodic table--

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the number of protons is
equal to the atomic number.

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And they put that
number up here,

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because that is the defining
characteristic of an element.

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The other two constituents
of an atom-- I

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guess we could
call it that way--

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are the electron
and the neutron.

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And the model you
can start to build

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in your head-- and this model,
as we go through chemistry,

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it'll get a little bit more
abstract and really hard

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to conceptualize.

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But one way to
think about it is,

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you have the protons
and the neutrons that

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are at the center of the atom.

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They're the nucleus of the atom.

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So for example, carbon,
we know, has six protons.

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So one, two, three,
four, five, six.

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Carbon-12, which is
a version of carbon,

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will also have six neutrons.

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You can have versions
of carbon that

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have a different
number of neutrons.

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So the neutrons can change,
the electrons can change,

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you can still have
the same element.

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The protons can't change.

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You change the protons, you've
got a different element.

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So let me draw a carbon-12
nucleus, one, two, three, four,

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five, six.

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So this right here is
the nucleus of carbon-12.

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And sometimes, it'll
be written like this.

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And sometimes, they'll actually
write the number of protons,

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as well.

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And the reason why we
write it carbon-12--

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you know, I counted
out six neutrons--

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is that, this is
the total, you could

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view this as the total number
of-- one way to view it.

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And we'll get a
little bit nuance

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in the future-- is that this
is the total number of protons

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and neutrons inside
of its nucleus.

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And this carbon, by definition,
has an atomic number of six,

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but we can rewrite
it here, just so

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that we can remind ourselves.

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So at the center of a carbon
atom, we have this nucleus.

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And carbon-12 will have six
protons and six neutrons.

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Another version of
carbon, carbon-14,

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will still have six
protons, but then it

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would have eight neutrons.

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So the number of
neutrons can change.

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But this is carbon-12,
right over here.

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And if carbon-12 is neutral--
and I'll give a little nuance

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on this word in a second
as well-- if it is neutral,

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it'll also have six electrons.

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So let me draw those six
electrons, one, two, three,

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four, five, six.

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And one way-- and this is
maybe the first-order way

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of thinking about
the relationship

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between the electrons
and the nucleus--

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is that you can imagine the
electrons are, kind of, moving

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around, buzzing
around this nucleus.

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One model is, you
could, kind of,

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thinking of them as
orbiting around the nucleus.

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But that's not quite right.

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They don't orbit the
way that a planet, say,

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orbits around the sun.

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But that's a good
starting point.

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Another way is, they're kind
of jumping around the nucleus,

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or they're buzzing
around the nucleus.

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And that's just
because reality just

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gets very strange at this level.

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And we'll actually have
to go into quantum physics

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to really understand what
the electron is doing.

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But a first mental
model in your head

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is at the center of this
atom, this carbon-12 atom,

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you have this nucleus,
right over there.

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And these electrons are
jumping around this nucleus.

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And the reason why these
electrons don't just

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go off, away from this nucleus.

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Why they're kind of
bound to this nucleus,

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and they form part
of this atom, is

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that protons have
a positive charge

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and electrons have
a negative charge.

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And it's one of these properties
of these fundamental particles.

00:10:01.874 --> 00:10:03.290
And when you start
thinking about,

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well, what is a
charge, fundamentally,

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other than a label?

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And it starts to
get kind of deep.

00:10:07.020 --> 00:10:08.810
But the one thing
that we know, when

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we talk about
electromagnetic force,

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is that unlike charges
attract each other.

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So the best way
to think about it

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is, protons and
electrons, because they

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have different charges,
they attract each other.

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Neutrons are neutral.

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So they're really just sitting
here inside of the nucleus.

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And they do affect the
properties, on some level,

00:10:30.700 --> 00:10:33.330
for some atoms of
certain elements.

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But the reason why we have the
electrons not just flying off

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on their own is
because, they are

00:10:37.970 --> 00:10:42.470
attracted towards the nucleus.

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And they also have an
unbelievably high velocity.

00:10:45.690 --> 00:10:48.630
It's actually hard for-- and
we start touching, once again,

00:10:48.630 --> 00:10:51.260
on a very strange
part of physics

00:10:51.260 --> 00:10:54.380
once we start talking about what
an electron actually is doing.

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But it has enough, I
guess you could say,

00:10:56.780 --> 00:10:59.690
it's jumping around enough that
it doesn't want to just fall

00:10:59.690 --> 00:11:04.520
into the nucleus, I guess is
one way of thinking about it.

00:11:04.520 --> 00:11:08.220
And so I mentioned,
carbon-12 right over here,

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defined by the
number of protons.

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Oxygen would be defined
by having eight protons.

00:11:12.710 --> 00:11:16.420
But once again, electrons can
interact with other electrons.

00:11:16.420 --> 00:11:19.140
Or they can be taken
away by other atoms.

00:11:19.140 --> 00:11:23.380
And that actually forms a lot of
our understanding of chemistry.

00:11:23.380 --> 00:11:26.400
It's based on how many
electrons an atom has,

00:11:26.400 --> 00:11:27.860
or a certain element has.

00:11:27.860 --> 00:11:29.580
And how those electrons
are configured.

00:11:29.580 --> 00:11:33.990
And how the electrons of
other elements are configured.

00:11:33.990 --> 00:11:36.490
Or maybe, other atoms
of that same element.

00:11:36.490 --> 00:11:41.180
We can start to predict
how an atom of one element

00:11:41.180 --> 00:11:43.360
could react with another
atom of that same element.

00:11:43.360 --> 00:11:46.700
Or an atom of one element,
how it could react,

00:11:46.700 --> 00:11:48.780
or how it could
bond, or not bond,

00:11:48.780 --> 00:11:51.370
or be attracted, or
repel, another atom

00:11:51.370 --> 00:11:52.630
of another element.

00:11:52.630 --> 00:11:55.230
So for example-- and we'll
learn a lot more about this

00:11:55.230 --> 00:12:00.110
in the future-- it is possible
for another atom, someplace,

00:12:00.110 --> 00:12:03.180
to swipe away an
electron from a carbon,

00:12:03.180 --> 00:12:05.840
just because, for
whatever reason.

00:12:05.840 --> 00:12:09.780
And we'll talk about certain
elements, certain neutral atoms

00:12:09.780 --> 00:12:12.360
of certain elements,
have a larger

00:12:12.360 --> 00:12:14.010
affinity for
electrons than others.

00:12:14.010 --> 00:12:17.140
So maybe one of those swipes
an electron away from a carbon,

00:12:17.140 --> 00:12:19.540
and then this carbon
will be having

00:12:19.540 --> 00:12:21.730
less electrons than protons.

00:12:21.730 --> 00:12:25.370
So then it would have five
electrons and six protons.

00:12:25.370 --> 00:12:28.152
And then it would have
a net positive charge.

00:12:28.152 --> 00:12:30.110
So, in this carbon-12,
the first version I did,

00:12:30.110 --> 00:12:33.170
I had six protons,
six electrons.

00:12:33.170 --> 00:12:34.530
The charges canceled out.

00:12:34.530 --> 00:12:37.170
If I lose an electron, then
I only have five of these.

00:12:37.170 --> 00:12:39.210
And then I would have
a net positive charge.

00:12:39.210 --> 00:12:41.241
And we're going to talk
a lot more about all

00:12:41.241 --> 00:12:42.990
of this throughout the
chemistry playlist.

00:12:42.990 --> 00:12:44.200
But hopefully, you
have an appreciation

00:12:44.200 --> 00:12:46.241
that this is already
starting to get really cool.

00:12:46.241 --> 00:12:48.300
Once we can already
get to this really,

00:12:48.300 --> 00:12:52.937
fundamental building
block, called the atom.

00:12:52.937 --> 00:12:55.520
And what's even neater is that
this fundamental building block

00:12:55.520 --> 00:12:58.800
is built of even more
fundamental building blocks.

00:12:58.800 --> 00:13:00.630
And these things
can all be swapped

00:13:00.630 --> 00:13:03.160
around, to change the
properties of an atom,

00:13:03.160 --> 00:13:05.880
or to even go from an
atom of one element

00:13:05.880 --> 00:13:08.466
to an atom of another element.