>> Hello. And welcome to
the Penguin Prof channel.
In today's episode,
I want to continue
to my basic chemistry concepts.
We're going to be talking about
bonds, all kinds of bonds.
Why atoms form them, what
kinds of bonds are possible,
and some more good stuff.
I want to make sure
everybody watched part one.
Did you watch part one?
Part one was really about
elements, the periodic table,
understanding atomic structure
and why it's all
about the electrons.
If you haven't seen it,
or you're unfamiliar
with those topics, check it out.
Otherwise, this can be a
little bit daunting, I know.
It can make your head spin
or in my case it can
make your Penguin spin.
We're going to try and
make some sense of it.
We're going to look at why
the noble gases are actually
so happy.
We looked at that before,
but we're going to explore
in this video how all the
other atoms try and become
as happy as the noble gases.
The noble gases, if you recall,
they are happy their
valence shells are full.
That is to say, everyone is
trying to attain this level
of stability that the noble
gases have all by themselves.
So, this is why they don't
play well with others.
But everybody else on the
periodic table has to bond
with other atoms to try to
attain that level of stability.
So, unless you're noble gas,
at the key to becoming happy is
atomic bonding, and that's kind
of where we left it last time,
and this is the topic we're
going to explore today.
The key to happiness
is a full valent shell.
Right. And of course,
you want to feel just
like a noble gas
even if you're not.
So, if you recall, the periodic
table and the valence electrons,
it's pretty easy because all
you have to do is look straight
down in these groups
or the columns,
and you see how many valence
electrons a particular element
will have that's going
to make it a lot easier.
So, the periodic table is your
friend, whether you want it
to be or not, it's going
to simplify your life.
Trust me on this.
We're going to look at different
ways that atoms play together,
ionically, covalently, and we're
going to look at hydrogen bonds.
And they're actually
very important in biology
because they hold a lot of
really important stuff together.
The first bond we're
going to look
at is the ionic bond,
taken, not shared.
So dramatic.
In ionic bonding, what's going
to happen is one atom is going
to donate one or more electrons,
and when that happens,
it's going to gain
a positive charge.
We're going to see why.
Meanwhile, another atom
is going to receive one
or more electrons, and it's
going to gain a negative charge.
Now, here's the key.
In chemistry, opposites attract.
So, it is the attractive force
between the positively charged
ion and the negative charged ion
that holds the whole
thing together.
That's the bond.
So, in their elemental
state, that is when you look
at the periodic table,
the atoms are all neutral.
Now, if an atom loses electrons,
one or more, it becomes an ion,
which means that it
has an electric charge.
And specifically,
it becomes a cation,
that is a positively
charged ion.
On the other hand, some atoms
will gain one or more electrons.
They also become ions, but they
will gain a negative charge,
and we use the term
anion to represent that.
If you've worked with
batteries, of course,
you're familiar with these.
Cathodes, anodes,
all the same thing.
So, the key is that these
opposite charges attract
each other.
That's where the bond is.
So, let's look at the classic
example of the ionic bond.
You know, textbooks act
as if there is only one
example, but we'll look at it.
Sodium and chlorine, you
notice they're at opposite ends
of the periodic table.
What we've got here is
a scenario where sodium,
remember the electrons
fill from the inside out,
and it's got a valent shell of
one electron, one lone electron.
This is not a happy situation.
Meanwhile, chlorine has
seven valence electrons
and would like to have eight.
It would like to feel
like a noble gas.
So, it is also very
unhappy, but when sodium
and chlorine get together,
something really
cool can happen.
Sodium can lose that
one electron.
Look what happens now.
Now its second shell, the
shell right here, is full.
So, sodium is happy.
Meanwhile, chlorine
gains an extra electron.
It then has a full valent shell
also, so it becomes happy.
Everybody is happy.
Now, the thing is,
don't forget though,
that sodium now has one less
electron than it has protons,
while chlorine has
one extra electron,
compared to the number
of protons.
That's where those
charges come into play.
So, now you notice that
this is not an atom anymore.
It's an ion.
It has a charge.
Specifically, it's a cation.
Chlorine is also an ion,
specifically it's an anion,
it is the attraction between
these two opposite charges
that holds sodium and
chloride together.
And you make salt.
I know, it's just
incredible how you make salt.
So exciting.
It's extremely stable because
sodium and chloride really
like to hang out together.
And you can see why.
Opposites attract.
If you look at another
example, calcium chloride,
now if you recall, this group
has two valence electrons,
and of course chlorine
still has seven.
So, you might already
start to think hmm,
if calcium has two
electrons in its valent shell,
and it could get rid of those,
that would also make
it stable and happy.
So, all you got to do in that
case is bind with not one
but two chloride ions in order
to achieve that stability.
So, calcium gives up its
two outermost electrons,
one to this chloride ion and
one to this chloride ion.
And the whole thing
is held together
in a very stable configuration.
That's calcium chloride.
So, sometimes electrons are
not taken but rather shared.
When that happens, we
refer to the sharing
of electrons as a covalent bond.
But immediately, you might
start to think, you know,
is sharing always equal?
Well, in humans,
certainly sometimes it is,
and sometimes it's not.
The same thing is
true for atoms.
So, sometimes the atoms exert
equal pulls on the electron,
and we refer to that
kind of a bond
as a nonpolar covalent bond.
We'll see why in a little bit.
Sometimes, one atom
has a stronger pull.
It wants the electrons more
than the other, so it kind of,
the electrons will kind of play
favorites because one atom is
so much more desirable
than another.
How do you know who
wants the electron more?
How can you predict that?
I mean how would you
ever know such a thing?
Oh, my God, it's on
the periodic table.
It turns out that as you go
across from left to right
and as you go up, you have
increasing electron affinity.
That means how much any
given atom wants electrons,
they want electrons so badly the
more you go towards this corner.
Remember, excluding
the noble gases,
because they're already
happy already.
So, who is at the
top right corner?
Oh, my gosh, it's fluorine.
Fluorine is the most
electron-desiring atom
in the whole periodic
table, and if you know that,
then this joke is
actually function.
Okay. Very geeky.
So, let's look at some covalent
bonds, and we're going to look
at the first one, hydrogen gas,
which I actually showed you
in the first video in my
chemistry concepts series.
Hydrogen is the smallest atom.
It has one electron
in its valent shell,
would like to have two.
So, one thing that hydrogen
can do is get together
with another hydrogen
atom and share electrons.
So, each one shares the
one electron that is has.
This is a typical
way that we draw it,
and when you see this little
line, this means one pair
of electrons being shared.
Okay, so that's what
those lines mean.
You're going to see
that all over the place.
Now, it turns out you can
share more than one pair,
so you can have a single, as
we just saw, but also a double
or even a triple bond.
Oh, I love gelato,
don't you love gelato.
This is reason to go to Italy.
If you go, make sure that
you look for this word,
[foreign language spoken],
which means that it's
actually hand made.
If you're going to eat gelato,
that's the only way to go.
Sorry, back to covalent bonds.
We're going to look
at carbon dioxide.
So, carbon, you recall, has four
electrons in its valent shell.
Oxygen has six.
So, in order for this
molecule to be stable,
you need to share more
than one pair of electrons
between the carbon and
each of the two oxygens.
So, this means that we
these two lines right here,
that represents two pairs
of electrons being shared,
and these two lines
here represent two pairs
of electrons being shared.
And now, if you count
up all the electrons
around each atom,
everybody is happy.
They all have eight electrons
in their valent shell.
What about oxygen gas,
oxygen has six electrons
in its valent shell.
So, if two oxygen atoms come
together in order for them
to have the full octet, they
also need to form a double bond.
And now, if you count around,
for each of the oxygens,
this line represents two, this
line represents two for four,
then you have five,
six, seven, eight.
Same thing for this guy.
So, everybody is happy.
Okay, let's look at one more.
How about nitrogen gas?
Now, nitrogen has five
valence electrons.
So, for nitrogen to
form covalent bonds
with another nitrogen, they
need to share three pairs.
So, two nitrogens will come
together and form a triple bond.
So, covalent bonds represent
sharing of electrons,
and so far all of this sharing
that we have looked at is equal.
These are nonpolar
covalent bonds.
What if the sharing is unequal?
We've got to talk about
this term polarity,
and hopefully the term polarity
makes you think about dualism
or something where there are
two sides that are different.
In biology, if you think
about mitosis, and you know
about the opposite poles
of a cell as it prepares
to divide, that could help.
Most people know about
the poles on the globe.
Of course, we have the
North Pole with polar bears,
and we have the South
Pole with penguins on it.
That's a pretty good example.
Now, if you didn't know that and
you thought there were penguins
at the North Pole,
don't feel bad.
It's not your fault.
It's because Hallmark puts
penguins on the Christmas cards
and with Santa it
drives me crazy.
Okay. Let's look at a situation
where electrons are
not shared equally,
as in the case of
hydrogen fluoride.
Remember, fluorine wants
electrons more than anybody else
on the periodic table.
So, let's look at hydrogen and
fluorine as they come together.
Hydrogen has one
valence electron.
Fluorine, of course, has seven,
and when they come together,
so this is fluorine
and this is hydrogen,
and this diagram is supposed
to represent the fact
that fluorine has such a
great pole on the electrons
that the redder color represents
the more negative side,
and the blue represents the more
positive side of this thing.
Now, these are not
electrical charges.
This is not an ion.
This is still a covalent
bond, but it's polar.
So, it means that one side of
the molecule is more negative.
The other side of the
molecule is more positive.
So, we call this a
polar covalent bond.
Another classic example of
polar covalent bonds, water.
Here's the oxygen, and
these are the two hydrogens,
and the oxygen exerts a
much greater electron pull
than the hydrogens.
So, the electrons prefer to
hang out more on this end,
so it makes this end, the
oxygen end, slightly negative.
The hydrogen end is
slightly positive.
And that's why water is polar.
I turns out that hydrogen bonds
are kind of related to this.
Hydrogen bonds are
weak interactions
between slight negatives
and slight positives.
Even if it's slight,
opposites still attract,
and it's actually
hydrogen bonds that account
for all the amazing
properties of water.
The fact that water
holds so much heat,
it has a high vaporization.
The fact that ice floats.
I mean, you probably don't think
about this too much
unless you are a penguin,
but it's something that other
substances don't do, right.
The solids are always more dense
than the liquids, so this is all
because of hydrogen bonding.
So, hydrogen bonds are
actually really important.
So, let's look at
water a little bit.
You know, the more I look at
it, I think water looks just
like Mickey Mouse, doesn't it?
I mean, maybe that's just mean.
I mean, if we orient
the Mickey Mouse heads,
wait a min, sorry, squirrel.
Okay, let's go back.
If you look at this,
on the oxygen end,
this end represents a
slight negative end.
This end, it's not shown here,
this is slightly positive,
but it's shown here,
this slight negative
and the slight positive,
they attract each other.
That, the dash lined,
that's the hydrogen bond.
And here's another one,
and here's another one,
here's another one.
These are the hydrogen
bonds between water that are
so important and give rise to
all of its amazing properties.
Hydrogen bonds are
important in other areas too.
Hydrogen bonds actually
hold DNA together.
That might surprise you,
because they're actually fairly
weak bonds.
But, it turns out that's really
important because DNA has
to unzip and open up in order
to do all the things
it needs to do.
Hydrogen bonds also
gives rise to a lot
of the structural
features we see in proteins
like an alpha helix and a beta
sheet, and in addition to that,
oh, my gosh, so much more.
Enzymes bind to substrates
because of hydrogen bonds,
and antibodies bind to antigens
because of hydrogen bonds,
and it goes on and on and on.
Hydrogen bonds turn out to be
really important in biology,
and you're going to see that as
you continue in your studies.
As always, I thank you
for visiting the
Penguin Prof channel.
I hope this was helpful.
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