>> 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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