Hi. This is Mr. Andersen. Today I am going to talk about chemical bonds. Chemical
bonds are attractions between either atoms or molecules. Now a little bit later we'll
talk about intermolecular bonds, so those are things that are attaching molecules together
but right now we're talking about straight up chemical bonds. In other words attractions
between atoms. I've pictured four of them on this diagram right here. Our four different
types are covalent bonds. So covalent bonds are going to be broken into two different
types. These ones right here would be polar, so I'm talking about the water itself or the
H2O. And then over here, this would be a non-polar covalent. Non-polar covalent, this is some
diesel fuel that's been spilled. It's actually C16H34. And so in a covalent bond what you're
doing is you're actually sharing electrons. You're not stealing electrons, but you're
sharing them. And it goes from sharing them very equally in a non polar bond to sharing
them very unequally in a polar bond. So these are the covalent bonds. Next one we'll talk
about are going to be ionic bonds. Ionic bonds. In ionic bonds bonds you're actually transferring
electrons between two different atoms and those become what are called ions. And those
ions are what are attracting it together. And so in this case we've got NaCl, or just
regular table salt. And that's an ionic bond. Now the other bond that's pictured here that
I won't talk about today are going to be metallic bonds. Metallic bonds are found within metals.
And they don't share their electrons. They kind of collectively share their electrons
so it gives them cool stuff like hardness and conductivity. And so we're not going to
talk about metallic bonds. But today I'm going to talk about covalent bonds, both non-polar
and polar and then ionic bonds. And mostly what I want to talk about today how do you
figure your what kind of bond it is. If you're just given the atoms, how do you know? Okay.
So I want to digress a little bit and talk about the octet rule in kind of a round about
way. When I was a kid, the most important toy you could have was Star Wars action figures.
Now I'm dating myself a little bit. In other words if you went over to a kid's house and
they had all these action figures it was going to be a great day because you knew they had
them all. And so what were the big ones? At least on the good side, the big ones you had
to have Chewbacca. You had to have a Hans Solo, Princess Leia. You had to have Luke
Skywalker. You got to have your C3-PO, Obi-wan Kenobi. Maybe you had the Yoda. And then you
had the R2-D2. Now if you had all eight of those you had a complete set. I remember flushing
my R2-D2 down the toilet just inadvertently and it was like one of the most sad days in
my whole life. And so if you had, let's say seven of the big eight action figures, you
really wanted that last to complete your set. And so atoms are the same way. And they have
what's called the octet rule. And so what does that mean? If you're oxygen, oxygen has
six electrons. It would love to have eight so, it's got 1, 2, 3, 4, 5, 6. It would love
to have eight. And so it can share those electrons with carbon and so it can have a complete
set. In other words, the secret of life or secret of chemistry, at least half of chemistry,
is that atoms are always searching out a complete outer level. In other words the want eight
electrons in the outside level. Now likewise, carbons, since it's got four, it's got 1,
2, 3, 4, it can share those with the other oxygen. And so in carbon dioxide, they both
have eight or all three of them have eight and so they're all happy. In other words,
it's like have a complete set of action figures and you're good to go. Okay, so how do you
know which type of a bond it is? Well this will vary a little bit depending on where
you get your stats. But these numbers are pretty important to remember. If you have
somewhere between an electronegativity difference of 0.5 and 0.0, it's a non-polar covalent.
If you're electronegativity differences are between 1.7 and 0.5 then it's a polar covalent.
And if it's above 1.7 then it's an ionic. Now first thing I need to talk about then
is electronegativity. What is electronegativity? Electronegativity is a measure of how much
you want electrons. And so the more electrons you want or the more you need those electrons,
the higher you're electronegativity is. And so fluorine up here, fluorine has 7 valence
electrons. That means if it can get one more valence electron it's going to have a complete
set. In other words it almost has all of the Star Wars action figures except maybe Yoda.
If it can get that last one, then it's going to be happy. And so the highest electronegativity
of everything up here is going to be fluorine. It has an electronegativity of 3.98. And so
as we move across the periodic table those numbers get larger. Also as we go up on the
periodic table it increases as well. So who doesn't want any electrons? Well it's francium.
Francium has an electronegativity of 0.7. That means it has one valence electron and
it doesn't need to hold on to it that much. In other words it would be easy to give off
that electron. It has a complete set right underneath it. And so it's going to be really,
really happy. And so by looking at the differences between the atoms and their electronegativity
differences, we can easily figure out what kind of chemical bond we have. So let's do
some for example. Let's do water. And so you know that water is H2O. So all we do is look
up the electronegativity of the two atoms. And so here's our hydrogen right here. Here's
our oxygen. Well oxygen's electronegativity, I'm just reading it on this chart, so in my
class you'd have to use your periodic table, it has an electronegativity of 3.44. I'm going
to subtract that of hydrogen, which is 2.20. And so I get a difference of 1.24. That's
the difference in their electronegativity between these two. So what kind of bond is
that? Well I look on my chart. It's somewhere between 0.5 and 1.7. And so I know immediately
that that's going to be a polar covalent bond in water. Let's go to another one. Here's
diesel fuel. This is centane. Diesel fuel is going to be C16H34. So if I look at, it's
hard to draw there, the bond between a carbon and a hydrogen, I just find them on the periodic
table. So carbon has an electronegativity on 2.55. In other words it wants the electrons
a little less then oxygen just did. Hydrogen has an electronegativity of 2.20. And so if
I find the difference between those two I get 0.35. And so what type of bond is found
in diesel fuel? Well it's less than 0.5 and so that's going to be a non-polar covalent.
That also explains why when you have diesel fuel and you pour it into water they don't
mix. Because one of them is non-polar and the other one is polar. And only likes will
attract to likes. Okay. Let's go to the last one. That's salt. Salt, what is salt? Salt
is NaCl. If we look up our electronegativity of salt, we're going to find sodium, oops,
all the way over here so it's 0.93. I'm going to then find chlorine. Chlorine is 3.16. Three
point one six. So I subtract 3.16 minus 0.93, as I try to do that in my head, that'd be
like two point what . . . 2.23. So it doesn't matter if I got my math right. We know that
that is greater than 1.7 so we know that' going to be an ionic bond. And so when you
look at salt, these are actually chlorine ions that are attracted to sodium cations.
In other words you've actually transferred that electron from the sodium to the chlorine
and so those like charges are attracting it. If we were to do one more, this in ammonia.
And so ammonia is NH3 and so you should be able to figure this one out. So first we look
up hydrogen. Then we look up nitrogen. And so the difference is going to be 3.04 minus
2.20. And so which one is it? Is it non-polar? Is it polar covalent? Or is it ionic?