Introduction to the atom

The atom, proton, neutron and electron

In most topics you have to get
pretty advanced before you

start addressing the
philosophically interesting

things, but in chemistry it
just starts right from the

get-go with what's arguably
the most philosophically

interesting part of the whole
topic, and that's the atom.

And the idea of the atom, as
philosophers long ago, and you

could look it up on the
different philosophers who

first philosophized about it,
they said, hey, you know, if I

started off with, I don't know,
if I started off with an apple

if I started of with a apple

and I just kept cutting
the apple -- let me draw a

nice looking apple just so
it doesn't look just

like a heart .

There you go.

You have a nice looking apple,
And you just kept cutting it,

smaller and smaller pieces.

So eventually, you get a piece
so small, so tiny, that you

can't cut it anymore.

And I'm sure some of these
philosophers went out there

with a knife and tried to do
it and they just felt that,

oh, if I could just get my knife
a little bit sharper, I

could cut it again and again.

So it's a completely
philosophical construct, which

frankly, in a lot of ways, isn't
too different to how the

atom is today.

It's really just a mental
abstraction that allows us to

describe a lot of observations
we see in the universe.

But anyway, these philosophers
said, well, at some point we

think that there's going to be
some little part of an apple

that they won't be able
to divide anymore.

And they called that an atom.

And it doesn't just have to just
be for an apple they said

this is true for any substance
or any element to that you

encounter in the universe.

And so the word atom is really
Greek for uncuttable.

Uncuttable or indivisible.

Uncuttable.

Now we know that it actually is
cuttable and even though it

is not a trivial thing, it's
not the smallest form of

matter we know.

We now know that an atom is
made up of other more

fundamental particles.

And let me write that.

So the we have the neutron.

And I'll draw in a second how
they all fit together and the

structure of an atom.

We have a neutron.

We have a proton.

And we have electrons.

Electrons.

And you might already be
familiar with this if you look

at old videos about atomic
projects, you'll see a drawing

that looks something
like this.

Let me see if I can draw one.

So you'll have something
like that.

And you'll have these things
spinning around

that look like this.

They have orbits that
look like that.

And maybe something that
looks like that.

And the general notion behind
these kind of nuclear drawings

-- and I'm sure that they
still show up at some

government defense labs or
something like that -- is that

you have a nucleus at the
center of an atom.

You have a nucleus at the
center of an atom.

And we know that a nucleus
has neutrons and protons.

Neutrons and protons.

And we'll talk a little bit more
about which elements have

how many neutrons and
how many protons.

And then orbiting, and I'm going
to use the word orbit

right now, although we'll learn
in about two minutes

that the word orbit is actually
the incorrect or even

the mentally incorrect way
of visualizing what

an electron is doing.

But the old idea was that you
have these electrons that are

orbiting around the nucleus very
similar to the way the

Earth orbits around the
Sun or the moon

orbits around the Earth.

And it's been shown that
that's actually

a very wrong way.

And when we cover quantum
mechanics we'll learn why this

doesn't work, what are the
contradictions that emerge

when you try to model an
electron like a planet going

around the Sun.

But this was kind of the
original idea, and frankly I

think this is kind of the idea
that is the most mainstream

way of viewing an atom.

Now, I said an atom is
philosophically interesting.

Why is it philosophically
interesting?

Because what we now view as the
accepted way of viewing an

atom really starts to blur the
line between our physical

reality and everything in the
world is just information, and

there really isn't any such
thing as true matter or true

particles as the way we define
them in our everyday life.

You know, for me a particle,
oh, it looks

like a grain of sand.

I can pick it up, touch it.

While a wave, that could be like
a soundwave. It could be

just this change in
energy over time.

But we'll learn, especially when
we do quantum mechanics,

that it all gets jumbled up as
we start approaching the

scales or the size of an atom.

Anyway, I said this was an
incorrect way of doing it.

What's the correct way?

So it turns out-- this is a
picture, not a picture really,

this is also a depiction.

So it's an interesting question,
what I just said.

How can you have a picture
of an atom?

Because is actually turns out
that most wavelengths of

light, especially the visible
wavelengths of light, are much

larger than the size
of an atom.

Everything else we
quote-unquote, observe in

life, it's by reflected light.

But all of a sudden when you're
dealing with an atom,

reflected light you could almost
view it as too big, or

too blunt of an instrument with
which to observe an atom.

Anyway, this is a depiction
of a helium atom.

A helium atom has two protons
and two neutrons.

Or at least this helium
atom has two

protons and two neutrons.

And the way they depict it here
in the nucleus, right

there, maybe these are the two--
I'm assuming they're

using red for proton and
purple for neutron.

Purple seems like more
of a neutral color.

And they're sitting at the
center of this atom.

And then this whole haze around
there, those are the

two electrons that helium
has, or that at least

this helium atom has.

Maybe you could gain or
lose an electron.

But these are the
two electrons.

And you say, hey, Sal, how can
two electrons be this blur

that's kind of smeared
around this atom.

And that's where it gets
philosophically interesting.

So you cannot describe an
electron's path around a

nucleus with the traditional
orbit idea that we've

encountered when we look at
planets or if we just imagine

things at kind of
a larger scale.

It turns out that an electron,
you cannot know exactly its

momentum and location at any
given point in time.

All you can know is a
probability distribution of

where it is likely to be.

And the way they depicted
this, black is a higher

probability, so you're much
more likely to find the

electron here than
you are here.

But the electron really
could be anywhere.

It could even to be here, even
though it's completely white

there, with some very, very,
very, very, very low

probability.

And so this function of where an
electron is, this is called

an orbital.

Orbital.

Not to be confused with orbit.

Orbital.

Remember, an orbit was
something like this.

It's like Venus going
around the Sun.

So it's very physically easy
for us to imagine.

While an orbital is actually
a mathematical probability

function that tells
us where we're

likely to find an electron.

We'll deal a lot more with that
when we cover quantum

mechanics, but that's not going
to be in the scope of

this kind of introductory set
of chemistry lectures.

But it's interesting, right?

An electron's behavior is so
bizarre at that scale that you

can't-- I mean, to call it a
particle is almost misleading.

It is called a particle, but
it's not a particle in the

sense that we're used to
in our everyday life.

It's this thing that you can't
even say exactly where it is.

It can be anywhere
in this haze.

And we'll learn later that there
are different shapes of

the hazes is as we add more and
more electrons to an atom.

But to me, it starts to address
philosophical issues

of what matter even is, or do
the things we look at, how

real are they?

Or how real are they, at least
as we've defined reality?

Anyway I don't want to get
too philosophical on you.

But the whole notion of
electrons, protons, they're

all kind of predicated on
this notion of charge.

And we've talked about it before
when we learned about

Coulomb's law.

You could review Coulomb's laws
videos in the physics

playlist. But the idea
is that an electron

has a negative charge.

A proton, sometimes
written like that,

has a positive charge.

And a neutron has no charge.

And so that's what was tempting
about the original

model of an electron.

If they say, OK, if this thing
has positive charges, right?

So let's say this is two
neutrons and two protons.

Let's say it's a helium atom.

Then we'll have some positive
charges here.

We have some negative
charges out here.

Opposite charges attract.

And so if these things had
some velocity, enough

velocity, they would orbit
around this, just the way a

planet will orbit
around the Sun.

But now we learn, even though
this is partially true, that

the further away an electron is
from the nucleus, it does

have more, it's true,
potential energy.

In that it will want to move
towards the nucleus, but

because of all the mechanics at
the quantum level, it won't

just do something simple like
move in a path like that, like

a comet would do around the Sun,
it actually has this kind

of wave-like behavior, where it
just has this probability

function that describes it.

But the further away
an orbital, it

does have more potential.

We're going to go a lot more
into that in future videos.

But anyway, how do you recognize
what an element is?

I've talked a lot about the
philosophy and all of that,

but how do I know that
this is helium?

Is it by the number of
neutrons it has?

Is it by the number
of protons it has?

Is it by the number
of electrons?

Well the answer is, it's by
the number of protons.

So if you know the number of
protons in an element, you

know what that element is.

And the number of protons,
this is defined

as the atomic number.

Now, so let's say I said
something has four protons.

How do we know what it is?

Well if we haven't memorized it,
we could look it up on the

periodic table of elements,
which we'll be dealing with a

lot in this playlist. And you'd
say, oh, four protons,

that is beryllium.

Right there.

And the atomic number is the
number that you see up there.

And that' s literally the
number of protons.

And that is what differentiates

one atom from another.

If you have fifteen protons,
you're dealing with

phosphorus.

And all of a sudden, if you
have seven protons, you're

dealing with nitrogen.

If you have eight, you're
dealing with oxygen.

That is what defines
the element.

Now, we'll talk in the future
about what happens with charge

and all of that.

Or what happens when you
gain or lose electrons.

But that does not change what
element you're dealing with.

And likewise, when you change
the number of neutrons, that

also does not change the element
you're dealing with.

But that leads to an obvious
question of, well, how many

neutrons and electrons
do you have?

Well, if an atom is
charge-neutral, that means it

has the same number
of electrons.

So let's say that
I have carbon.

Its atomic number is six.

And let's say its mass
number is twelve.

Now what does this mean?

And let me say further that this
is a neutral particle.

This is a neutral atom.

So the atomic number
for carbon is six.

That tells us exactly how
many protons it has.

So if I were to draw a little
model here, and this is in no

way an accurate model.

I'll draw six-- two, three,
four, five, six

protons in the center.

And the weight of these protons,
each proton is one

atomic mass unit, and we'll
talk more about how that

relates to kilograms.
It's a very small

fraction of a kilogram.

Roughly I think it's
1.6 times 10 to the

minus 27th of a kilogram.

So let's say each of these are
one atomic mass unit, and

that's approximately equal to,
I think, 1.67 times 10 to the

minus 27 kilograms. This
is a very small number.

It's actually almost impossible
to visualize.

At least it is for me.

This tells me the mass of the
entire carbon atom, of this

particular carbon atom.

And this can actually
change from carbon

atom to carbon atom.

And this is essentially the
mass of all of the protons

plus all of the neutrons.

And each proton has an atomic
mass of one, in atomic mass

units, and each neutron
has an atomic mass of

one atomic mass unit.

So this is really the number
of protons plus

the number of neutrons.

So in this case we have six
protons, so we must also have

six neutrons.

Six neutrons plus six protons.

Now, where are the electrons?

Well, I said it's neutral, so
the proton has an equal

positive charge as the
electron's negative charge.

So this is a neutral atom, and
it has six protons, so it also

has six electrons.

Let me draw that.

So we said it has six
neutrons in here.

One, two, three, four,
five, six.

So that's the nucleus
right there.

And then if we were to draw the
electons-- well, I could

draw it as a smear, but if we
want to kind of visualize it a

little better, we could say,
OK, there's going to be six

electrons orbiting.

One, two, three, four,
five, six.

And they're going to be moving
around in this unpredictable

way that we would have
to describe with

a probability function.

And so the interesting thing
about it is, most of the mass

of an atom is sitting
right in here.

I mean, you might notice that
when people care about the

mass, when they care about the
atomic mass number of an atom,

they ignore the electrons.

And that's because the mass
of a proton, one proton

mass-wise, is equal
to 1,836 electons.

So for thinking about the mass
of an atom, for all basic

purposes, you can ignore the
mass of an electron.

It's really the mass of the
nucleus that counts as the

mass of the atom.

Now, you might see this periodic
table here, and you

say, OK, they gave us the
atomic number up there.

The atomic number of
oxygen is eight.

It means it has eight protons.

The atomic number of
silicon is 14.

It has 14 protons.

Now what is this right here?

Let's see, in carbon.

In carbon they have
this 12.0107.

That is the atomic
weight of carbon.

Let me write this.

Atomic weight of carbon.

The atomic weight of
carbon is 12.0107.

Now, what does that mean?

Does that mean that carbon has
six protons and then the

remainder, the remaining 6.0107
neutrons, it has kind

of this fraction of a neutron?

No.

It means if you were to average
all the different

versions of carbon you find on
the planet and you were to

average the number of neutrons
based on the quantity of the

different types of carbon,
this is the

average you would get.

So it turns out that carbon, the
two major forms, the main

one you'll find is carbon-12.

So that's like this.

So that has six protons
and six neutrons.

And then another isotope
of carbon.

Now an isotope is the same
element with a different

number of neutrons.

Another isotope of carbon is
carbon-14, which is much more

scarce on the planet.

We don't know how much in the
universe, but on the planet.

Now, if you were to average
these, not just a straight-up

average, then you would get
carbon-13 and then the atomic

weight would be 13, but you
weight this one much higher

because this exists in much
larger quantities on Earth.

I mean, this is pretty
much all of the

carbon that you see.

But there's a little
bit of this.

So if you weight them
appropriately, the average

becomes this.

So most of the carbon you'll
find-- if you just found

carbon someplace, on average
its weight in atomic mass

units is going to be 12.0107.

But that idea of an isotope
is an interesting one.

Remember, when you change the
neutrons, you're not changing

the actual, fundamental
element.

You're just getting a different
isotope, a different

version, of the element.

So these two versions of carbon
are both isotopes.

Now, I want to leave this video
with what I think is

kind of the neatest idea behind
atoms. And it's the

most philosophically interesting
things about them.

It's that the relative size--
so, we have these electrons,

which represent very little
of the mass of an atom.

It's 1/2000 of the mass of an
atom are the electrons.

And even those, it's hard
to even describe them as

particles, because you can't
even tell me exactly where and

how fast one of these
particles is moving.

They just have a probability
function.

So most of the atom is sitting
inside the nucleus.

And this is the interesting
thing.

If you look at an atom
on average, if you

say this is my atom.

Let's say I had two atoms that
are bonded to each other.

And I were to say, how much
of this is actual stuff?

And when I say stuff, that's a
very abstract concept, because

we're talking about the
nucleus, right?

Because the nucleus
is where all the

mass is, all the stuff.

It turns out that it's actually
an infinitesimally

small fraction of the volume of
the atom where-- the volume

of the atom is hard to define,
because the electron can

pretty much be anywhere, but
if you view the volume as

where you're most likely to find
the electron, or with 90%

probability you're likely to
find the electron, then the

nucleus is, in a lot of cases
and the way I think about it,

it's about 1/10,000
of the volume.

So if you think about it, when
you look at something, if you

look at your hand or if you
look at the wall or if you

look at your computer, 99.99%
of it is free space.

It's nothing.

It's vacuum.

If you had ultra-small-- I
guess we could call them

particles or something-- most
of them would pass straight

through whatever you look at.

So it already starts to kind of

question our hold on reality.

What is there when, if-- and
this is fact, this isn't

theory right here-- that if you
take anything down to the

building blocks, down to the
atomic level, most of the

space of that kind of,
quote-unquote object, is free

vacuum space.

You could go straight through
it if you could get down to

that scale.

This image of a helium atom,
they say right here this is

one femtometer.

Right?

One femtometer.

This is the scale of
the nucleus of a

helium atom, right?

One femtometer.

This is one angstrom, right?

And they say that equals
100,000 femtometers.

And just to get a sense of
scale, one angstrom is 1 times

10 to the negative
10 meters, right?

So the atom is roughly on the
scale of an angstrom.

In the case of helium,
the nucleus is

even a smaller fraction.

It's 1/100,000.

So if you had-- let's say you
had liquid helium, which you'd

have to get very cold to get.

If you're looking at that,
most of it is free space.

If you're looking at an iron
bar, the great, great, great,

great, great, great majority
of it is free space.

And we're not even talking
about, maybe there's some free

space inside the nucleus
that we could talk

about in the future.

But to me, that just blows my
mind that most things we look

at are not really solid.

They're really just empty space,
but they look solid

because of the way light
reflects on them or the forces

that repel us.

But there really isn't something
to touch there.

That most of this right here
is all free space.

I think I've said the word free
space now, and I think

I'll leave further

mind-blowing to the next video.