- [Instructor] All right.
Atoms.
So as we discussed in lecture one,
the lowest level of complexity
that we study with biology is atoms.
We don't go deeper than that.
That's for physics and whatnot.
But in nature, you
don't deal with energies
that cause atoms to interact in such ways
that they split up into
their smaller constituents,
and you know, into quarks and muons
and other things of that sort.
So this lecture is gonna
be all about answering one,
big question, why do atoms
interact with one another
to form larger, complex structures
which we call molecules?
Because as we've discussed,
molecules such as water
and organic molecules such
as carbohydrates and fats,
those are gonna be in
the next few lectures.
So it's important that
we understand why atoms
interact with one another in various ways,
or maybe, why don't they
interact with one another,
as we'll show.
And within the answers are
various theories and principles
you're gonna learn.
Which is why in lecture two
we discussed the difference
between a hypothesis,
theory and principle.
Okay, so you can see a periodic table.
Everybody's pretty familiar with this.
You can see many of the elements,
some of them are not shown here
because they would have their
own separate rows down below.
But usually, anything over 92,
or after the 92nd element
is pretty much man-made.
So there are about 92
naturally current elements
that exist on our planet.
Well, where were those
elements first created?
They were created in the stars.
They're essentially, stars are reactors
that compress hydrogen
and helium into more
dense atomic structures
with a higher weight to them,
and therefore, different properties.
And so pretty much, the
naturally occurring elements
come from stars.
They go supernova.
They disperse these atoms
throughout the universe.
And that's what forms the
galaxies and the planets
and the moons and everything else.
Well, we're not so concerned in biology
about every single element.
You're gonna see a lot of
them as we go through here,
especially ones that play a
particular role to you and I
such as calcium and sodium and potassium,
and things of that sort that are necessary
for our body to be able to function.
But when you really break it down,
there are six fundamental elements.
And we went over these before,
but we'll go over 'em again.
That all living things have.
And I like the mnemonic, CHNOPS
In fact, most of them are right
here on the periodic table.
These five, and then hydrogen
which is way over there.
So CHNOPS are carbon, nitrogen, oxygen,
phosphorous and sulfur,
and then hydrogen.
Those are the six elements that no matter
which living organism you dissect down
and break it down into
its fundamental element,
you will find all six of those.
So these are the six,
basic elements or atoms
that make up all of life.
Now obviously, there's
more to it than those six,
but that's the commonality
in all living things
is they have these six elements that form
the fundamental molecular structures.
So we have to discuss a
little bit about chemistry
and how atoms interact with one another
before we can really understand,
you know, the property
of these higher structure,
these molecules.
Now this is gonna be a small
crash course in chemistry
if you haven't taken it in awhile.
Or in even if you have taken it,
there are things you're gonna learn
that you won't have learned in chemistry
because of how they apply to biology.
So don't turn your brain off
just because you're like, "I
already no about covalent bonds
"and things like that."
Guarantee you there's new
things you're gonna learn
that you didn't learn from
your basic chemistry class.
So let's talk about matter.
Let's talk about the nature
of matter and energy.
Because matter and energy
are one and the same.
How do we know this?
Einstein's famous equation.
Most people know it,
but they don't really quite understand it.
What does E equals MC square mean?
It means that matter and
energy are the same thing.
They're just different
manifestations of it.
You can turn energy into matter
and matter into energy.
So they are, tell you, it's a lot easier
to turn matter into energy
than it is to turn energy into matter.
But they are interchangeable.
All right, so matter is any
anything that takes up space.
And we'll look at the
smallest parts of an atom
such as the protons and the
neutrons and the electrons.
That's what we talk about
when we talk about matter.
Energy, on the other hand,
is the ability to do work.
And in lecture seven, we're gonna spend
a considerable amount of time
looking at the differences
between potential energy
and kinetic energy.
Now kinetic energy, this is
just to give you an idea,
is usually movement, movement
of certain particles.
Heat, light, electricity,
all of these are manifestations
of kinetic energy.
But today, we're gonna focus primarily
on what we call potential energy
which is stored energy.
And this is where we
get into chemical bonds
or the interactions that
atoms have with one another.
Why do they interact with one another?
Because that's what forms the
fundamental chemical bonds.
Which there are three of
that we'll talk about today
that form all molecules.
Now not all molecules are organic,
but in life, we're gonna talk
about all of the organic molecules
and how they have their various properties
such as carbohydrates
and fats and proteins.
All right, each organism,
though it has the six,
same basic elements,
do not have the same amount even.
In some organisms, they might
have a little less oxygen,
a little more carbon and whatnot,
but all six of them are gonna be there.
Let me illustrate again the concept
that it doesn't mean either
that these six elements
are the most abundant.
For example, calcium in the
human body, 2% of your matter
that makes you up is calcium.
But only 1.1% and .9% make
up phosphorus and sulfur.
So it's not about abundance,
it's just about what is
actually found there.
Okay, so let's dissect this down.
This'll be one of your first questions,
just to test you on your
fundamental understanding
of the nature of atoms.
There's only one question
on this on your test,
but it's necessary just to make sure
you have the fundamentals down.
An atom is made up of three main parts.
Most atoms, hydrogen may not,
it may missing a part, but most
atoms have three main parts.
In the nucleus, or the center of the atom,
are your protons and your neutrons.
This is what formed the mass of the atom.
So each atom has its own particular mass
that is determined by
the nature of the amount
of protons and neutrons.
The more protons and neutrons it has,
the heavier it is, the heavier elements
and things of that sort.
In fact, that's how they are able
to separate radioactive isotopes
to be able to do things
like uranium enrichment
with centrifugalization
and things of that sort
because there's a difference in mass
between radioactive uranium
and basic uranium and whatnot.
So that's what forms the bulk
of matter in all of the atoms
in all of your body in any of the organism
is the neutrons and the protons.
Now the protons are what
determined the properties
of the atoms.
Protons ultimately
determine one main thing,
how many electrons are
surrounding the nucleus.
Now electrons are not
massless, but almost.
Okay, they don't have
very much mass at all.
But these electrons, these particles
as they travel around, they're
very strange particles.
Because in certain instances,
they behave like particles,
in others, they behave
like an energy wave.
That gets more into quantum mechanics
than we really need to in this class.
So that's why I said
that protons and neutrons
are really what formed the
bulk of the mass of an atom
because for all intents and purposes,
electrons are almost massless,
though they do have mass.
All right, so let's talk
about protons and neutrons
and why the atom's properties
are determined by the number
of protons and not the number of neutrons.
Neutrons, as the name suggests,
don't have any charge to them.
But protons do.
They have a positive charge to them.
And as such, they attract electrons,
and electrons have a negative charge.
There's this interaction so to speak.
Well, the number of protons in the nucleus
predetermines how many electrons
are gonna be surrounding it.
If there's six protons in the nucleus,
there's six electrons
surrounding the atom.
If there's eight, there's eight.
Now that brings us another point as well.
Each atom has what we call an isotope.
That will come up on one or two questions.
Not everybody will get that,
but you need to know what isotopes are.
So what is an isotope?
Isotopes have the same number of protons.
Like carbon-12, that's
the most abundant carbon
on our planet.
But there are other forms of carbon.
There's carbon-13, and the
more well-known one, carbon-14.
So what's the difference
between those atoms?
Carbon-12 has six
protons and six neutrons.
Carbon-13 has six protons
and seven neutrons.
And carbon-14 has six
protons and eight neutrons.
They're all carbon which means
that they behave the same.
They all behave like a carbon atom does.
The main difference is these
carbons are a little heavier,
slight bit heavier because they have one
or two more neutrons.
So isotopes are atoms that have
the same number of protons,
but different number of neutrons.
We use this for things like carbon dating.
Because when an organism dies,
the carbon-14 starts to
decay at a very precise rate.
And we can actually determine not,
it's not good for long, long-term.
It's only good for a
few thousand years or so
before it starts becoming obsolete.
But carbon dating can
allow us to reliably look
at how long an organism
essentially has been dead.
We now use other radioactive isotopes
that have a much longer half-life
in which we can use for
radiometric dating of fossils
and things in the earth's crust.
All right, so isotopes.
Make sure you understand.
The protons are what determine
the properties of the atoms.
Isotopes have the same number of protons,
but different number of neutrons.
Okay, so that's fundamentals of atoms.
That's just what atoms are made of.
Now, let's address the
question of why atoms
interact with one another.
So some of you will get
that question on your quiz,
where it'll literally say,
"Why do atoms interact with one another?"
Well, before we can answer that question,
we have to talk about a theory.
It's called valence electron shell theory.
And this theory essentially describes
how electrons orbit
the nucleus of an atom.
The reason why we're not exactly sure
how electrons orbit the nucleus
is because they're so small
and they're so lightweight,
so to speak, that we can't
follow where they're going.
And this is where quantum
mechanics really becomes difficult
is because we cannot know precisely
where the electron is
and where it's going.
This brings us to a principle
called the Heisenberg
uncertainty principle.
And if you've watched "Breaking Bad",
that's why he calls himself Heisenberg
because chemistry and whatnot.
Heisenberg uncertainty
principle is that the more
you know about where an electron is,
the less you know about where it's going.
And the more you know
about where it's going,
the less you know about
where it came from.
So you can know the speed,
but you can't know its
position at the same time.
You can know its position,
but you can't know its speed.
So that's one of the biggest issues
that we deal with, is the
more we know about one aspect
of the electron, the less
we know about the other.
It just is not possible yet
to get to that.
So that's the Heisenberg
uncertainty principle.
That just describes why we
don't know where exactly
all of the electrons are going,
or where they are at any given moment.
However, we can take snapshots of it.
And therefore, we know relatively,
the area that the electrons are found in.
And we call these valence electron shells.
And that's where we
get into the valence
electron shell theory.
So valence electron shell theory
is more than just, you know,
where the electron's found.
Again, that's the Heisenberg
uncertainty principle.
So what is the valence
electron shell theory?
Well, it explains why atoms
interact with one another.
All atoms follow this rule.
You have the nucleus of the atom.
The first shell, as we call it,
the closest area around the nucleus
can only hold two electrons.
Now we may not know exactly
where those electrons are in that orbital,
but we know it can only hold two.
There's two in that area
going around somewhere.
The next shell can hold eight electrons.
So the way in which all atoms function
is as it increases the number of protons
in its nucleus, it also increases
the number of electrons,
respectively, as I mentioned.
If you have six protons,
you also have six electrons.
So as the electrons orbit,
the electrons first fill up this shell.
Then any leftover fill up this shell.
Now if you have more than 10,
it goes to the third.
And that's the extent of what
we're gonna do in this class
is the third one.
The third one also follows this rule,
that it can hold eight.
Now it doesn't evenly
distribute them between these.
If you have 10, it
doesn't do like one here,
four there, and four there.
It always fills up the first,
then the second.
And if there's more, it goes to the third.
Now obviously, there's
more and more after this.
But it gets beyond what we need to cover
for this class.
So you're only gonna
go up to three shells,
so to speak.
Two in the first, eight in the second,
eight in the third.
So if you have some like carbon
which has six protons in its nucleus,
here's the other thing to be wary of.
Because we're dealing
with isotopes sometimes.
Let's say I give you a question
where I talk about
carbon having six protons
and eight neutrons,
like an isotope.
Well, sometimes people
make the mistake of saying,
"Oh, there's eight electrons."
No, the electrons are directly correlated
to the number of protons.
So there's always,
no matter what the
neutrons are of an atom,
it follows the rule of
electron per proton.
Okay, so in this scenario,
you don't have a third shell.
So it has six electrons.
It'll put two in the first,
and how many in the second?
It only has four left.
Now here is where valence
electron shell theory comes
into play to explain why atoms
interact with one another.
An atom that does not have a full
outer valence electron shell
is considered unstable.
It's not in a stable way.
It needs the outermost shell
filled up to capacity.
There are multiple ways
to accomplish this.
The first way is to steal electrons
from other atoms.
So if carbon were to
steal four more electrons
from other atoms, then it would fill
up that outermost shell and become stable.
Well, it typically doesn't do that.
We'll explain another way in a second,
how that does.
Another way to become stable
is to give up electrons.
Sometimes atoms are so close,
let's say we have something like lithium,
where it has three protons.
And therefore, it'll have two electrons
and one in its outermost shell.
It's much easier to get rid of
that one electron.
And now, it defaults
down to this first shell.
And that's fine too.
All it needs is a complete outer shell
filled with electrons to capacity.
That's valence electron shell theory.
That the outermost shell most be filled
to capacity for the atom to become stable.
Now some atoms are naturally stable.
We call these noble elements.
You know, how nobility doesn't interact
with the peons and things like that.
I'm not kidding.
These are called noble gases.
So helium, neon, argon.
Let's look at these.
The number above the atom
tells you how many protons.
Notice we're ignoring
the neutrons in this.
We're more concerned with the protons
because of the behavior of the atom.
So let's look at helium.
It has two protons.
So therefore, how many
electrons does it have?
Two.
As such, helium will not
interact with other atoms.
Now we can force it to
if we cool it down enough
to like negative 271
degrees celsius, okay?
Absolute zero, like where there's like,
so like no movement or energy
is negative 273 degrees celsius.
So pretty close.
You slow them down enough
that you can actually start
forming liquid helium,
so to speak.
They interact with one another.
But it has to get freaking
cold for that to occur.
So helium, you don't get helium structures
interacting with one another,
or helium interacting with other atoms
because it's a noble gas.
Let's look at neon.
Neon has 10 protons.
So how many electrons does
it have surrounding it?
It has 10, all right.
How many in the first shell?
How many electrons in the first shell?
- [Student] Two.
- [Instructor] Two.
How many in the second.
It's stable because the outermost shell
is filled to capacity.
It has eight electrons in it.
Let's look at argon.
Has 18 protons.
So how many electrons does
it have in the first shell?
Two, how many in the second?
And how many in the third?
- [Class] Eight.
- [Instructor] These are the noble gases.
They do not interact with other atoms.
And the same thing is true for these,
but again, this goes beyond
what we need to for this class.
That means that all other atoms
are unstable, and the only
way they can become stable,
according to valence
electron shell theory,
is to do something to fill
up their outermost shell.
So I told you about one aspect.
They can lose electrons, like
lithium and sodium usually do.
They can steal electrons,
like oxygen, fluoride and
chloride typically do,
or, and this is where we get into
the idea of larger structures,
they can share electrons.
And when they share electrons,
they form tight, strong bonds
that cause them to form larger
structure called molecules.
And that's really the idea here.
So let's look at this.
You're going to have a question
on valence electron shell theory,
actually two questions.
One will ask you to fill up the shells
based upon information
I give you regarding
what's in the nucleus of the atom.
So as you can see, as I mentioned,
hydrogen's one of the most
naturally occurring element.
Hydrogen doesn't even have any neutrons,
but that doesn't matter
'cause it has a proton.
Hydrogen pretty much is
just a single proton.
Carbon, notice we're not
showing the neutrons here.
But carbon has six protons.
And nitrogen, seven.
Eight for oxygen.
You can see how the valence
electron shells fit.
If you've got these little circles,
that means it's a vacancy.
It's missing two to become stable.
So that's what your observing
here is this needs three
to become stable.
Carbon needs four to become stable,
to fill up that outermost shell.
All right, so let's do a sample question.
Everyone will have one like this
on your quiz.
But there are a variety of
different circumstances,
different atoms that I'm gonna give you.
But the overall structure
of it is exactly the same.
So these are just several
examples showing you
these are the six electrons
that are in all living things.
So that's why they're shown here.
And it illustrates the filling
up of valence electron shells
with the electrons showing the vacancies.
So let's talk about how atoms
may steal or lose electrons.
This deals with the formation
of what we call ionic bonds.
Okay, so there are three types
of bonds you're gonna learn today:
ionic, covalent, and hydrogen bonds.
The two out of these three
have a major role in biology.
But as we'll learn, ionic
bonds don't really form
that much in any biological system.
They do on occasion,
but for the most part, they don't.
And the reason for that
is because ionic bonds
are strong until you put them in water,
and then they get broken up very easy.
Well guess what?
All living things are made up
of somewhere between 70 to 90% water.
So ionic bonds don't really
form in living cells,
in living organisms because of that.
Because we're mostly water.
If you've ever seen a cadaver,
they're much smaller
and shorter than they
were in really life, why?
Because they're missing most of the water
that made them up.
You know, they're desiccated and whatnot.
So they're like four-foot,
where they used to be
six-foot and whatnot.
Okay, so ionic bonds.
Let's talk about that.
First, before we get to ionic bonds,
let's talk about how an ion forms.
An ion is a stable,
well, for the most part.
I'm gonna shoot myself in the foot here.
An ion is an atom that has
gained or lost electrons.
So here's what happens.
When there is a disproportion
to the number of protons to electrons,
then, like basic math,
if you have 11 and then negative 10,
you end up having a net of one.
Or if you have something like 17 protons
and you have more electrons,
then you have a net of one,
but on the negative side.
An ion is an atom that typically
has lost or gained electrons
to try to become stable.
So sodium chloride are two
prime examples of this.
Sodium has 11 protons to it.
As such, it has 11 electrons.
Well, let's fill up the shells.
How many in the first?
- [Class] Two.
- [Instructor] Two,
how many in the second?
- [Class] Eight.
- [Instructor] Eight,
how many in the third?
- [Class] One.
- [Instructor] One.
What's easier, to get seven more electrons
to fill up that third shell,
or to dump that one off and
just default down to this one?
Dump the one off.
So sodium loves to give up that electron,
but as a result of becoming stable,
it no longer has the same proportion
of protons to electrons
and therefore becomes positively charged.
Chloride on the other hand,
does the opposite.
It has 17 protons.
So therefore, 17 electrons.
Two in the first.
Eight in the second.
And seven more in the third.
It just needs one more.
More than happy to take
that electron from sodium,
but in the process of doing so,
becomes negatively charged.
So these two atoms become
positively and negatively charged.
But they're stable.
And that's really what they're after.
That's what valence
electron shell theory is.
That's why ions form, is
because sodium now is stable,
and chloride now is stable.
But now you have two atoms
that have opposite charges.
Well, just like magnetic poles
or any elements when there
are opposite charges, opposites attract.
So this is what forms the ionic bond.
An ionic bond is the attraction
between oppositely charged ions.
Now just like opposites
attract, like repel.
So if you have two ions
that are of the same charge,
they're not attracted to one another,
they'll actually repel
just like two magnets.
If you they're to put them together,
the North poles, they'll repel.
They create the field
that repels one another.
Okay, so salt is one of the
prime examples of ionic bonds.
When you have sodium and chloride,
they will form this lattice,
a perfect, square lattice structure.
If you look at salt crystals,
they are perfectly square
because they form this structure
of alternating sodium and chloride atoms
that all interact with one another
due to their positive and negative forces.
Now, you can let salt
sit there on your table
for a thousand years, and it
will still stay together, okay?
Ionic bonds are strong.
However, the moment you
put it into, say, water,
they start breaking apart.
And so when we describe
the properties of water,
you'll see why.
But that's one of the
weaknesses of ionic bonds,
is when you put them into
a watery environment,
they immediately start
breaking apart, okay?
So that's why ionic bonds typically
don't form in human cell tissues.
There are certain scenarios
where you do get ionic bonding.
And I'll tell you what those are later on.
But most, you don't have
salt crystals forming.
In fact, if you do, you're screwed
because that means that the
salt concentration is so high
that your cells are probably dying.
So all right, now I got
a dumb joke to tell you
to help you remember this.
A sodium ion walks into a bar
and asks the bartender for
the phone to call the police.
He's all beat up and whatnot.
He tells the bartender, "I've
been mugged," and whatnot.
And as he's on the phone with the police,
the bartender's asking him questions.
He's like, "Are you absolutely sure
"that you got mugged?
"What happened"
He was like, "Oh, I was walking down
"and chloride just ripped
one of my electrons from me,
"you know, and whatnot."
He just like, "Well, are you sure?"
He was like, "Yeah, I'm positive."
All right.
So.
(class chuckles)
It was funny.
So I tell that joke to my dad
probably once every other month,
and he still laughs like for five minutes.
But he's an electrical
engineer, so he loves it.
Anyway, all right, so sodium chloride,
salt, that's not the only
type of ionic bond out there.
Obviously, there are many
types of ions out there.
But it just gives you the
idea of an ionic bond.
All right, now let's look at
the more common type of bond
that forms you and I.
And that is a covalent bond.
These are the strongest types
of interactions between atoms.
So what happens is a lot of atoms
don't want to give up their electrons.
And even if another atom tries
to steal those electrons,
it holds onto them pretty tight.
As such, when these types
of atoms come together,
instead of ripping electrons away from one
and stealing them, they just share them.
But in order to share them,
they have to be in close
proximity to one another
so that the electrons
can surround and travel
from one atom to the
other very, very rapidly.
So it requires a close
association between the atoms
which is what forms the covalent bonds.
As you can see with the
elephants and the peanut here.
They both want it.
They both want it really bad.
As such, it's going to
be shared between them.
Now unlike this scenario,
the peanut, or the electron,
doesn't just sit between the atoms.
It circles the atoms.
So in this scenario,
it's missing one of the most
important elements of it.
And this is the only reason
why I really don't like some
of these two dimensional images
is because the electrons
are not just sitting there.
They're actually moving.
They're moving from atom to the next
and one atom to the next.
Again, we don't know exactly how,
Heisenberg uncertainty principle,
but we do know that they
are going around the atoms
at the speed of light pretty much.
Okay, so let's look at carbon.
'Cause carbon is of
those elements that forms
the fundamental structure
for all organic molecules,
from carbohydrates, to fats, to proteins
to your genetic material
which we call DNA.
So the reason why carbon
is such a key element
is because unlike some
of the other elements
like oxygen, carbon is kind
of right at that midpoint
where it has four vacancies
in its outermost shell,
but it's not like lithium
where it only has a few and
it'll give away that outer one.
And it's not like oxygen
where it has most of the valence
electron shell filled up,
and so it only needs a couple more.
It's right at that midpoint.
So carbon can form large, large structures
with other atoms because it has just
the right amount of vacancies
in its outermost shell,
which is four in this case.
So here's a simple example, methane.
Methane is CH4.
What happens is carbon,
having four vacancies,
needs to share electrons with other atoms
it comes in contact with
in order to become stable.
Well, hydrogen, hydrogen's
an interesting atom.
As it only has one proton,
it therefore only has one electron.
Now here's the thing you have
to understand about hydrogen.
You can't go down to zero, to nothing.
You'd be like, "Oh, why
doesn't it just give up
"that one electron?"
No.
According to valence
electron shell theory,
you have to at least have one shell.
So unlike sodium,
where it can lose its third
and go down to a second,
or unlike lithium, where
it could lose its second
and go down to its first,
hydrogen cannot get rid
of its one electron.
So its only solution is
to share another electron
because even though it
only has one proton,
it still needs two electrons
in that first shell
to become stable.
All right.
So where does it get it from?
Well, when the hydrogens
come in close contact with the carbon,
they all start sharing their
electrons with one another.
Carbon will share one of its electrons
with each hydrogen.
And hydrogens will share
their electrons with carbon.
As I mentioned, they're not just sitting
in between the atoms.
They're constantly circling them.
But for all intents and purposes,
carbon has eight in its outermost shell,
and hydrogen has two.
And as long as they
stay in close proximity
to one another and continually
share these electrons,
they are all stable.
And that's why covalent bonds,
which is the sharing of two
electrons between atoms,
that's the definition of a covalent bond.
The sharing of two
electrons between atoms,
that's why they're so strong.
Because if you try to
pull one of those atoms
away from that molecular structure,
it resists it because you're
basically trying to destabilize
that atom by removing
it from that sharing.
And that's why covalent bond,
which is pretty much what makes you you,
all of the connections that
make all of the molecules
that make you up hold together.
And takes a considerable
amount of energy to break that.
Now yes, you can break a covalent bond.
In fact, if we couldn't
you and I wouldn't be here.
That's what we do when we eat.
We are breaking the
covalent bonds from our food
to extract the energy because
there's a lot of stored energy
in covalent bonds.
So when you eat sugars and fats,
there's just long, long strings,
especially with fat,
long, long strings of carbon
that can be broken up
and the energy can be extracted
from those covalent bonds.
So a covalent bond is usually indicated
by a dash between two atoms.
Here, you're seeing the
valence electron shell model,
but in future times,
you'll see it like this.
Where the atoms will have
a single dash between them.
Now a double dash means that
there's two covalent bonds.
And that's because they're
sharing four electrons
between each other.
So here, carbon is sharing
four electrons with oxygen,
two with nitrogen,
and two with that carbon.
So it's sharing all eight of its electrons
in its outermost shell between these atoms
so that this can be stable
and that one and that one.
And that's what forms
that molecule and whatnot.
Now, this brings us to another point
of what you're gonna be tested on.
You will be tested on
covalent bonds as well,
so let me recap.
Covalent bonds are the strongest bond.
There is a question on your quiz
that will test you relative strengths.
It'll say which is the strongest bond?
Which is strong, but can
be easily broken in water?
Or what's the weakest type of bond?
We haven't talked about
the weakest one yet.
So covalent bonds.
Also, another thing you gotta
know about covalent bonds.
It's not just sharing of electrons,
but due to the nature of the sharing,
it stores energy.
This is a critical aspect for biology
because this means that
the larger the molecule,
the more energy is stored.
That's why pound for pound,
fats have more energy than sugars
because condensed in the space
that the fats take up,
there are more covalent bonds.
As such, it's more dense,
has more energy that
you can get from that.
Everybody likes the carbohydrates more
because it's easier to break down,
but there's more energy in fats
than there is in sugars.
Okay.
Now, another thing to bring up.
The more covalent bonds a molecule has,
so now we're getting into molecules.
I mean, it's not the molecule lecture.
But as atoms interact with one
another and share electrons,
they form more complex
structures called molecules.
Now there are some molecules
that are very simple, like ethanol.
There are others that are
more complex, like caffeine.
There are different elements of nitrogen,
carbon, oxygen, and hydrogen and whatnot.
But the more covalent bonds per molecule,
the more energy that molecule has.
Now one of the biggest
things that confuses people
is I'll ask something
of the nature of between
a single acetylene molecule
and a caffeine molecule,
which one has more stored energy?
And most people choose the acetylene
because they're used to the idea
that due to the fact
that when you break this triple
covalent bond of acetylene,
yeah, you get a lot of energy.
However, to be able to create that energy,
you don't just break one.
You're breaking billions of
these triple covalent bonds.
Well, due to the nature of caffeine,
you can't really do that.
Due to the chemical structure.
However, if you were
to simultaneously break
all of these covalent bonds in caffeine
compared to the single acetylene,
you would have a much
larger release of energy.
Now, it doesn't happen chemically.
So the concept is there's
more stored energy
in a single caffeine molecule
than there is a single acetylene molecule.
And that's where people
tend to get confused.
They're like, "No, we
use acetylene torches
"and all that kind of stuff."
That's because these are very easy
to break billions of these
molecules in an instant
and release a tremendous amount of energy.
If you did the same thing with caffeine,
the same quantity,
I'd say look out.
'Cause it's a considerable
amount of energy.
So the more covalent
bonds that a molecule has,
the more energy a molecule has.
When you look at something
like a sugar molecule, like
glucose, that's glucose.
There, that's glucose.
What does a fat look like?
Actually, it goes about
three times more of that,
and so on and so forth.
You can start to see why fats
have more energy to them
per molecule, per
triglyceride than sugars do
per sugar, per glucose or whatnot.
All right.
Let's see.
Now, let's get to the last
and final type of bond.
James Bond, the strongest.
No.
Actually, I have that as
one of my dummy questions,
so please don't choose it.
You know, what's the
strongest type of bond?
And I have James down there.
(class laughs)
So, all right.
Electronegativity.
Each atom has its own
attraction for electrons.
Now this gets, again, into
more of the particulars
that you don't need to know
the actual electronegativity of an atom.
But it needs to be brought up
so you understand the next concept.
Every atom has a particular pole
or attraction for electrons.
The stronger that pull,
the more likely that atom
is to rip the electrons from another atom.
For example, look at chloride here.
There's a very strong
attraction for electrons.
Look at sodium.
There's a very week
attraction for electrons.
As such, when you put these two together,
that's why the chloride rips
the electron from the sodium.
And they're both happy
because they're stable.
They become ions.
When you deal with something
more like carbon and hydrogen,
they're about equal.
I know it doesn't look so on there,
but for all intents and purposes,
they're about equal.
Which means that when they
share their electrons,
then they're equally sharing
them between one another.
However, when you start dealing
with something like oxygen
and hydrogen, like H2O,
there's a difference.
You no longer are sharing
the electrons equally.
When oxygen and hydrogen
form a covalent bond,
which they do,
it's not the same as the covalent bond
between a carbon and a hydrogen, okay?
So let me explain the difference.
Oxygen and hydrogen,
any sharing of electrons is
considered a covalent bond.
However, if the sharing is unequal,
we call it a polar covalent bond.
So why do we call it
a polar covalent bond?
It's because polarity is when due
to the unequal sharing of
electrons between the atoms,
you end up getting slight charges
on the atoms.
It's not ionic, but it does
create what we call a polarity.
So let's look at oxygen and hydrogen here.
Due to the strong attraction that oxygen
has for electrons,
the electrons will
spend more of their time
in the valence electron shells of oxygen
than they will of hydrogen.
Well, just as we discussed,
when you start getting that imbalance
between the number of electrons
and the number of protons,
it starts becoming negatively
or positively charge.
So it doesn't actually steal
the electron from hydrogen.
But due to the fact that it
has stronger affinity for it,
the oxygen ends up
having a slight negative
charge to it, slight.
And so we usually put
something like that in it.
Hydrogen, as a result as well,
having less attraction for the electron,
it spends less time around it.
And it ends up having a
slight positive charge to it.
Well, this is where H2O comes into play.
So the attraction between
the hydrogen and the oxygen,
or the electrons that are being shared,
those are what we call
polar covalent bonds.
Now, for all intents and
purposes, they're a covalent bond,
just like any other.
However, due to the unequal sharing,
it causes the atoms to become
slightly charged, slightly.
Not immensely, but just slightly.
And that leads us to our
third and final bond,
which is called a hydrogen bond.
Yeah, this is probably one
of the most difficult ones to explain
because people, it's just hard to wrap
your head around why we
call it a hydrogen bond.
Let me first explain
what a hydrogen bond is,
and then I'll tell you why
we call it a hydrogen bond.
Now, let me simplify this a little bit.
We have an oxygen and two hydrogens.
The hydrogens have a slight
positive charge to them.
The oxygen has a slight negative charge
to it when you have two
polar molecules, like water,
due to it's polarity,
there is an attraction
similar to an ionic bond,
but not as strong.
As such, this weaker attraction
is called a hydrogen bond, okay?
So opposites attract, we know that.
Just like with the ionic bonds.
However, due to the fact
that these are not ions,
they're just slightly charged,
then there is a weaker attraction
between them, all right?
And these hydrogen
bonds are very transient
which means they're constantly
being broken and remade.
The water molecules are constantly moving
around one another.
So there is a slight attraction
to each other, a very weak
attraction to each other.
It's not as solid as an ionic bond.
It's not as strong as an ionic bond,
far from it.
It's one of the weakest.
So that polarity of the
molecules is what creates
the hydrogen bond.
Now before you imagine
that water's the only one
that creates hydrogen bonds.
Let me show you,
let me show you where else
hydrogen bonds are found.
So let me show you water here.
'Cause that's our next lecture,
is on the properties of water.
And in fact, the majority
of the properties of water
are due to hydrogen bonding,
this weak attraction
between the polar molecules.
You'll notice that they're
constantly breaking and moving.
That's what liquid water is.
The molecules are always
breaking and remaking
new hydrogen bonds.
So it's weak.
But when you collectively get trillions
of water molecules together,
then they stay enough with one another
that it forms the liquid
that makes life possible, or H2O.
But DNA, which is your genetic material,
also has its properties
due to hydrogen bonding.
The majority of your DNA is held together
by covalent bonds.
But the inner workings,
the two parts of your DNA
that actually form this double helix,
are held together by hydrogen bonds.
That's what creates the
double helix of your DNA.
Proteins which pretty much make you you,
yes, the atoms are held
together by covalent bonds.
But due to the polarity of this molecule,
then it starts forming
these loops and helices
that are created because
of hydrogen bonding.
Otherwise, you just have
these flat molecules,
this very linear molecules.
But due to hydrogen bonding,
they creates loops and whirls.
And that's what gives proteins their shape
and their function.
So when we get to organic molecules,
you'll start to see its application.
But you've got to, for this quiz at least,
you basically have to know the differences
between covalent, ionic,
and hydrogen bonds.
