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Mr. Andersen shows you how to determine if a bond is nonpolar covalent, polar covalent, or ionc.
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Transcript Provided by YouTube:
00:03
Hi. This is Mr. Andersen. Today I am going to talk about chemical bonds. Chemical
00:08
bonds are attractions between either atoms or molecules. Now a little bit later we’ll
00:14
talk about intermolecular bonds, so those are things that are attaching molecules together
00:18
but right now we’re talking about straight up chemical bonds. In other words attractions
00:22
between atoms. I’ve pictured four of them on this diagram right here. Our four different
00:28
types are covalent bonds. So covalent bonds are going to be broken into two different
00:35
types. These ones right here would be polar, so I’m talking about the water itself or the
00:42
H2O. And then over here, this would be a non-polar covalent. Non-polar covalent, this is some
00:52
diesel fuel that’s been spilled. It’s actually C16H34. And so in a covalent bond what you’re
01:01
doing is you’re actually sharing electrons. You’re not stealing electrons, but you’re
01:05
sharing them. And it goes from sharing them very equally in a non polar bond to sharing
01:10
them very unequally in a polar bond. So these are the covalent bonds. Next one we’ll talk
01:15
about are going to be ionic bonds. Ionic bonds. In ionic bonds bonds you’re actually transferring
01:21
electrons between two different atoms and those become what are called ions. And those
01:28
ions are what are attracting it together. And so in this case we’ve got NaCl, or just
01:33
regular table salt. And that’s an ionic bond. Now the other bond that’s pictured here that
01:38
I won’t talk about today are going to be metallic bonds. Metallic bonds are found within metals.
01:44
And they don’t share their electrons. They kind of collectively share their electrons
01:48
so it gives them cool stuff like hardness and conductivity. And so we’re not going to
01:54
talk about metallic bonds. But today I’m going to talk about covalent bonds, both non-polar
01:58
and polar and then ionic bonds. And mostly what I want to talk about today how do you
02:02
figure your what kind of bond it is. If you’re just given the atoms, how do you know? Okay.
02:07
So I want to digress a little bit and talk about the octet rule in kind of a round about
02:13
way. When I was a kid, the most important toy you could have was Star Wars action figures.
02:19
Now I’m dating myself a little bit. In other words if you went over to a kid’s house and
02:24
they had all these action figures it was going to be a great day because you knew they had
02:28
them all. And so what were the big ones? At least on the good side, the big ones you had
02:32
to have Chewbacca. You had to have a Hans Solo, Princess Leia. You had to have Luke
02:37
Skywalker. You got to have your C3-PO, Obi-wan Kenobi. Maybe you had the Yoda. And then you
02:42
had the R2-D2. Now if you had all eight of those you had a complete set. I remember flushing
02:49
my R2-D2 down the toilet just inadvertently and it was like one of the most sad days in
02:54
my whole life. And so if you had, let’s say seven of the big eight action figures, you
03:01
really wanted that last to complete your set. And so atoms are the same way. And they have
03:07
what’s called the octet rule. And so what does that mean? If you’re oxygen, oxygen has
03:13
six electrons. It would love to have eight so, it’s got 1, 2, 3, 4, 5, 6. It would love
03:22
to have eight. And so it can share those electrons with carbon and so it can have a complete
03:28
set. In other words, the secret of life or secret of chemistry, at least half of chemistry,
03:35
is that atoms are always searching out a complete outer level. In other words the want eight
03:40
electrons in the outside level. Now likewise, carbons, since it’s got four, it’s got 1,
03:45
2, 3, 4, it can share those with the other oxygen. And so in carbon dioxide, they both
03:54
have eight or all three of them have eight and so they’re all happy. In other words,
03:57
it’s like have a complete set of action figures and you’re good to go. Okay, so how do you
04:03
know which type of a bond it is? Well this will vary a little bit depending on where
04:07
you get your stats. But these numbers are pretty important to remember. If you have
04:11
somewhere between an electronegativity difference of 0.5 and 0.0, it’s a non-polar covalent.
04:18
If you’re electronegativity differences are between 1.7 and 0.5 then it’s a polar covalent.
04:23
And if it’s above 1.7 then it’s an ionic. Now first thing I need to talk about then
04:28
is electronegativity. What is electronegativity? Electronegativity is a measure of how much
04:33
you want electrons. And so the more electrons you want or the more you need those electrons,
04:41
the higher you’re electronegativity is. And so fluorine up here, fluorine has 7 valence
04:47
electrons. That means if it can get one more valence electron it’s going to have a complete
04:53
set. In other words it almost has all of the Star Wars action figures except maybe Yoda.
04:57
If it can get that last one, then it’s going to be happy. And so the highest electronegativity
05:02
of everything up here is going to be fluorine. It has an electronegativity of 3.98. And so
05:08
as we move across the periodic table those numbers get larger. Also as we go up on the
05:13
periodic table it increases as well. So who doesn’t want any electrons? Well it’s francium.
05:18
Francium has an electronegativity of 0.7. That means it has one valence electron and
05:25
it doesn’t need to hold on to it that much. In other words it would be easy to give off
05:30
that electron. It has a complete set right underneath it. And so it’s going to be really,
05:34
really happy. And so by looking at the differences between the atoms and their electronegativity
05:39
differences, we can easily figure out what kind of chemical bond we have. So let’s do
05:44
some for example. Let’s do water. And so you know that water is H2O. So all we do is look
05:51
up the electronegativity of the two atoms. And so here’s our hydrogen right here. Here’s
05:56
our oxygen. Well oxygen’s electronegativity, I’m just reading it on this chart, so in my
06:01
class you’d have to use your periodic table, it has an electronegativity of 3.44. I’m going
06:07
to subtract that of hydrogen, which is 2.20. And so I get a difference of 1.24. That’s
06:16
the difference in their electronegativity between these two. So what kind of bond is
06:20
that? Well I look on my chart. It’s somewhere between 0.5 and 1.7. And so I know immediately
06:27
that that’s going to be a polar covalent bond in water. Let’s go to another one. Here’s
06:32
diesel fuel. This is centane. Diesel fuel is going to be C16H34. So if I look at, it’s
06:41
hard to draw there, the bond between a carbon and a hydrogen, I just find them on the periodic
06:46
table. So carbon has an electronegativity on 2.55. In other words it wants the electrons
06:51
a little less then oxygen just did. Hydrogen has an electronegativity of 2.20. And so if
06:59
I find the difference between those two I get 0.35. And so what type of bond is found
07:05
in diesel fuel? Well it’s less than 0.5 and so that’s going to be a non-polar covalent.
07:11
That also explains why when you have diesel fuel and you pour it into water they don’t
07:15
mix. Because one of them is non-polar and the other one is polar. And only likes will
07:21
attract to likes. Okay. Let’s go to the last one. That’s salt. Salt, what is salt? Salt
07:28
is NaCl. If we look up our electronegativity of salt, we’re going to find sodium, oops,
07:35
all the way over here so it’s 0.93. I’m going to then find chlorine. Chlorine is 3.16. Three
07:40
point one six. So I subtract 3.16 minus 0.93, as I try to do that in my head, that’d be
07:50
like two point what . . . 2.23. So it doesn’t matter if I got my math right. We know that
08:07
that is greater than 1.7 so we know that’ going to be an ionic bond. And so when you
08:13
look at salt, these are actually chlorine ions that are attracted to sodium cations.
08:19
In other words you’ve actually transferred that electron from the sodium to the chlorine
08:24
and so those like charges are attracting it. If we were to do one more, this in ammonia.
08:31
And so ammonia is NH3 and so you should be able to figure this one out. So first we look
08:39
up hydrogen. Then we look up nitrogen. And so the difference is going to be 3.04 minus
08:48
2.20. And so which one is it? Is it non-polar? Is it polar covalent? Or is it ionic?
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This post was previously published on YouTube.
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Photo credit: Screenshot from video.