>> Hello, Welcome to the
Penguin Prof Channel.
Today I want to get started
on a chemistry concept series.
By popular demand, we're going
to be talking about elements,
atoms -- really why it's
all about the electrons
and some Lewis Dot Structures,
which in my opinion may
be the key to happiness.
When we get started here
we're really talking
about what stuff is made of.
And stuff is made of matter.
From here you can really kind
of go off a cliff in terms
of how far you want
to go into this.
This is really the
realm of physics.
So I just want to
say from the outset
that this is a highly
abbreviated version
of an understanding of what
the stuff is in the universe.
The matter is made of elements.
Elements are pure chemical
substances that you can't break
down into anything else.
Now we organize elements in
this amazing table called
"The Periodic Table
of the Elements".
It's really amazingly organized.
And I'm just going to
say it -- it's beautiful.
OK, how much of a
geek am I to say that?
But it really is, because if
you understand how this table is
organized, this is
tremendously powerful.
Notice I didn't say
if you memorize it.
I do not have my students
memorize any part of this table.
That's what it's there for.
That's why you can look it up.
But you have to understand how
to use it and what it means.
In terms of elements in the
universe, the vast majority
of them are the two smallest
elements -- hydrogen and helium.
On our planet, in
the Earth's crust
by weight we've got oxygen,
silicon and aluminum.
If you take the Earth as a
whole, not just the crust --
by weight the most
abundant element is iron.
In terms of biology only 25
elements are essential for life
and of those 25, only four
make up the vast majority
of most living things
-- including penguins.
So if you're wondering,
well what are we made of?
You'll be thrilled to know that
you can actually buy a shirt
with human ingredients on it.
Oh my gosh, I love
these geeky gifts.
I don't know what that
barcode is at the bottom,
but anyway so here's
a nicer view --
a table of the elements
of the human body.
And again you can see that over
96 percent of humans are made
of oxygen, carbon,
hydrogen and nitrogen.
So if you go back to the
periodic table and it is kind
of overwhelming, I admit -- but
you remove all of the elements
that are not found in humans,
it's really not too bad at all.
This looks somewhat
manageable right?
Understanding the periodic
table also allows you
to understand all these
stupid geeky gifts.
Like this bacon shirt,
which I just --
I don't know, I was
just in a weird mood.
OK, so this smallest unit of
an element, which retains all
of the properties of that
element, is called an atom.
That work comes from the Greek.
A term which means --
not to be divisible.
Meaning you can't cut it
up into smaller pieces
and still retain the
properties of the element.
We can actually see atoms today.
This is a really cool
transmission electron micrograph
done by the physicists
at UC Berkley.
The red arrows are hydrogen,
that black arrow is
a carbon atom shown
on the surface of graphene.
Now in your textbook you will
see atoms drawn like this.
Electron clouds, the shell
or Bohr model and I got
to be honest with you --
this is just not true,
atoms do not look like this.
We use these drawings
because they represent sort
of an easier way for
us to talk about them,
but this is not what
atoms really look like.
Atoms are really hard
for us to wrap our brains
around because they
are unbelievably small.
That black bar right here at the
bottom represents one angstrom
or 100,000 centimeters.
So an angstrom is 10 to
the minus 10th meter.
And the vast majority of the
atom is actually empty space.
So over 99 percent of the mass
of the atom is concentrated
at the center in the nucleus.
And the rest of it
where the electrons are,
the orbitals are just
hugely spread out
and it is really difficult for
us to really draw and think
about what atoms
really look like.
So I have a couple of
analogies for you, of course.
One is an analogy of scale.
And this is a soccer field
and if you take the nucleus
to be the size of
the soccer ball,
then an electron can be a fly
buzzing around the spectators.
And most of the stadium
represents the space
between the atomic
nucleus and the electron,
so most of the atom
is empty space.
Now this analogy is not
really accurate either
because it shows the electron
as a particle -- as a fly.
And actually that's not true.
One of the best analogies
that a chemist gave me
for this is with cotton candy.
And he said, "OK,
where's the sugar?"
Well, the sugar's
kind of everywhere.
I mean the whole cotton
candy is made of sugar.
That's kind of the same
idea with these electrons.
So the orbital itself
really is the electron.
But that's really hard
to draw and describe.
So what I always say is, you
know, strive for understanding.
Strive for the real truth.
But we -- like all
of your textbooks
and basically everybody else --
we're going to use these models
and drawings, we're going
to draw the little electron
as like a ball or a bead so that
we can keep track of everything.
OK, but realize that
that's not really the truth.
So getting back to the atoms
and the periodic table,
there's a couple of
numbers that we need
to concern ourselves with.
One is the atomic number.
And that's just the number of
protons that an element has.
And I'm picking carbon
here as an example.
The atomic number
for carbon is six.
What that means is that
carbon has six protons.
That number does not change.
It's kind of like
your calling card.
So if you add a proton to
carbon, it's not carbon anymore.
So now you're atomic
number would be seven,
and now you're nitrogen.
So the atomic number
does not change.
The mass number or what we
call the atomic weight --
that's the number of protons,
plus the number of neutrons.
The first thing that
you notice is
that these numbers are decimals.
So maybe you're wondering --
well are there fractional
protons and fractional neutrons?
And, you know, what's
up with that?
Well, what we're really getting
at here is the mass number
is actually an average.
So the number of protons does
not change, but the number
of neutrons can change.
So if we look at carbon --
carbon in the universe --
there are different
numbers of neutrons
in various carbon atoms
that you could find.
We call these isotopes.
Most carbons in the
universe have six neutrons.
And of course the number
of protons doesn't change.
So 6 plus 6 is 12.
So the vast majority of carbons
that you would find have
the mass number of 12.
You will also find
though, some carbon atoms
with an extra neutron.
And if you add 6 plus 7, that
gives you the mass number of 13.
Some atoms have two
extra neutrons.
Two more than the normal number.
And the mass number here is 14.
This is probably the one that
you're most familiar with.
Carbon-14 is what
we use for dating.
Not dating, will you
go out with me --
but dating, how old
is that tree?
We use isotopes for all
kinds of purposes actually --
in medicine, as well
as radioactive dating
because they decay
at a constant rate.
So if you look at a
decay rate of carbon-14,
this is what it means.
So we have time zero --
some amount of carbon-14
that's present.
After one half-life --
which for carbon-14 is
about 5,000 years -- after
one half-life, you have half
that amount still remaining.
After two half-lives, you
have half of that half.
And after three half-lives
you have another half.
So it's not live after two
half lives it's all gone.
That's a big misconception.
So what you should notice is
this exponential rate of decay.
And this rate is constant.
So that's why we can use
isotopes to date living tissue,
to date rocks and
things like that.
But enough about the nucleus,
chemistry is really
all about electrons.
So we're going to spend the rest
of this video talking
about them.
Now atoms like to be stable.
And in order to become
stable, sometimes they have
to play with other atoms.
In this way they're
kind of like people.
But you might ask the question,
does everybody need to play
with others in order
to be happy?
Humans are social
creatures so most of us do,
but there are actually
individuals that don't.
And the same thing is true
in the periodic table.
We have to the far
right the noble gases.
Noble gas is so named
because like nobility,
they do not mix with
the commoners.
And in this video we're
going to explore why.
Why don't they form
bonds with other atoms?
Everybody else on the
table -- they form bonds,
but not the noble gases.
You got to understand
the electrons
in order to understand why.
So, electrons fill around the
nucleus from the inside out.
And what I mean by that is as
you look at different atoms
and different atoms
have different numbers
of electrons -- they will fill
around those nuclei
from the inside out.
Just like water fills
in a glass.
When you fill a glass with water
it fills from the bottom up.
OK, you can't do
it any other way.
If you can I'd like to see that.
Shell number one is going
to hold two electrons.
Shells two and three
are going to hold eight.
Yes, for you chemists I
am over-simplifying this.
When you go on and take more
general chemistry, you will see
that the electron configurations
are a little more complicated
than that, but for the
purposes of general biology,
what I'm giving you should get
you through most of the problems
that you're going to
come in contact with.
I just got to say don't
get your heart rates
up when you see stuff like this.
Even at first glance, you
notice that there is a pattern.
So there really --
this is manageable.
But we're not going to go
into that in this video.
We're going to focus
on happiness.
What you got to remember
is that atoms are happy
when they're outer shell
is full of electrons.
The outer shell turns out to be
so important we actually
give it a name.
We call it the "valence shell".
So we're going to talk about how
they get to be happy right now.
As we go through this,
we're going to see
that carbon is not happy
by itself, where neon is.
We're going to see why.
My analogy for this is
stadium in the Round.
So a stadium with a stage inside
and spectators all the way
around and of course we're going
to have penguins in there too.
So we're going to have
a rule and a goal.
The rule is we're going
to sell tickets closest
to the stage first.
The goal is we want
to make each shell
around the stage
full of spectators.
Now, in our little
theater it's going
to be a very little theater.
The first shell is only going
to have two seats in it.
The second shell is
going to have eight seats
and the third shell is also
going to have eight seats.
So just go with me on this, OK?
It's a small intimate theater.
So here are our seats.
We're going to look
at different scenarios
and see what it looks like.
So here's the first scenario
-- we sell one ticket.
So we're going to
satisfy the rule,
the tickets that
we sell are going
to be closest to the stage.
The goal is not met though,
so that's not so happy.
We have one empty
seat in the first ring
and this is actually hydrogen.
Another scenario --
we sell two tickets,
so the rule is they're going to
be the ones closes to the stage,
so that's all good and
we actually met the goal.
The shell is full.
So that's a really
happy stable scenario
and this is actually
the element helium.
What if we sell seven tickets?
So notice the rule,
we're selling the tickets
closest to the stage first.
But you notice now that
we have three empty seats
in that second shell.
So this is nitrogen.
This explains why nitrogen
would want to form bonds to try
and fill those empty seats.
What if we sell 10
tickets though?
Now you notice that the
first two shells are full --
this a very stable configuration
and this is actually
the noble gas neon.
What about 13 tickets?
So now we're moving
into that third shell.
We're always filling
from the inside out,
but now that third shell has
only three occupied seats
and five empty ones.
So that's not so happy and
that is the element aluminum.
And our last example,
we have 18 seats.
And you notice we have
all three shells full.
This is a very stable
configuration.
This is the noble gas argon.
So maybe you've noticed
that it seems to be
about the valence shell.
If the valence shell
is so important,
why don't we just focus on that?
I mean who cares what the
core of the beast look like?
Let's just look at the outer
shell since that's what's going
to determine how
happy an atom is.
If you're thinking that, that's
awesome, you're not alone
because some other really smart
people have thought exactly the
same thing, like Dr. Gilbert
Lewis, who's a physical chemist,
he spent most of his
career at U.C. Berkley.
And he did exactly that.
He said, "We should
draw elemental symbol
and then we're going to draw
the valence shell electrons
around it."
And I always tell my students --
if you keep track of the
valence electrons you're going
to be happy.
So let's see how this works.
We're going to look at carbon.
The most important part in terms
of carbon's reactivity
is the valence shell.
So let's just get rid
of everything else.
And we're going to
draw only the electrons
in the valence shell
around carbon.
That's the most important part.
So carbon has the
atomic number six.
And now you know that two
of those electrons are
in that first shell, leaving
four for the valence shell.
Now I just want to
remind you those penguins
represented electrons.
But for heavens sakes
don't draw penguins
in your Lewis Dot
Structures, you're going
to get kicked out of class.
So what we do is we
draw literally dots
around the element to represent
the valence electrons and --
ta-da that is the Lewis
Dot Structure for carbon.
How easy is that?
So let's look at nitrogen.
So to draw the Lewis
Dot Structure
for nitrogen all you do is you
draw the symbol for nitrogen
and then you go around it
and draw the valence electrons
starting at the top --
now this -- how you
draw these varies --
this is the was that I was
taught, starting at the top
and going around --
nitrogen looks like that.
So let's look at aluminum.
So here's the symbol
for aluminum.
Aluminum has three
electrons in its valence shell
so you draw them
around going one, two,
three -- that's aluminum.
So finally let's do argon.
Argon has a full valence shell,
so we're going to draw one, two,
three, four, five,
six, seven, eight --
a full valence shell for argon
and it's as simple as that.
So check this out.
If you look down the column
of all the noble gases
and you draw the Lewis Dot
Structures for each one,
you will find that
they all look the same,
because all of them have
full valence shells.
And this explains why all
the noble gases are happy
as they are and they don't
form bonds with other atoms.
Because if the goal is to
have a full valence shell
and you already have one, you
don't need to play with others.
The only thing that might
confuse you is helium,
and what you have to remember
is that helium is very small --
atomic number two -- so
it has only two electrons.
And so you have to remember
that, that first shell is
in fact full with two.
Where as everybody else
going down this group --
they will all have an outer
shell full with eight.
So let's practice.
When you practice drawing
the Lewis Structures,
all you need -- without the
penguins -- is a periodic table.
So lithium -- atomic
number three,
is going to have two
electron in the first shell,
leaving you one in
the second shell.
So when you draw the Lewis
Dot Structure, that's it --
one electron in the
valence shell.
For oxygen, you've got two
electrons in the first shell,
six in the second
for a total of eight.
So you draw your oxygen with
one, two, three, four, five,
six electrons in
the valence shell.
That's your Lewis Dot
Structure for oxygen.
Sodium has two in the first
shell, eight in the second,
one in the third,
for a total of 11.
Sodium is drawn just like that.
So it's really not too bad.
And even though most biology
instructors don't really show
you Lewis Dot Structures,
you're going to have to do it
in Chemistry anyway
and truthfully
if you understand
Lewis Dot Structures --
everything else is going
to make a lot more sense.
So here are the first
20 elements
and the Lewis Dot
Structures for each.
And what you notice
is that as you go
down the vertical columns,
which we call groups,
they all have the same
Lewis Dot Structures
and that explains why they have
the same chemical reactivity
and why they'll form
the same kind of bond.
Isn't that cool?
How powerful is that?
So understanding Lewis
Dot Structures is going
to make predicting atomic
interactions so much easier
and you're going to be able to
predict what's going to happen
when -- for example two
hydrogen atoms get together,
because unless you're a noble
gas, you're going to have
to play with others in
order to become happy.
And that's what atomic
bonding is.
And that's why two
hydrogen's get together
to form H2 -- hydrogen gas.
So they're both going to
share their lone electron,
so that each one can
have a stable full shell.
As always, I hope
this was helpful.
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