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Course: High school chemistry > Unit 5
Lesson 1: Electronegativity and bond polarityElectronegativity and bond type
A covalent bond involves the sharing of electrons between two atoms, but they typically are not shared equally. The difference in electronegativity between the two atoms defines whether a bond is classified as nonpolar covalent or polar covalent. Created by Sal Khan.
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- I am unsure if this is correct. As my friend explained, if the result of subtraction falls between 0.4-1.7, it is a covalent bond, but if it is above 1.7, it is an ionic bond.
Is this right?:))(5 votes)- Hi, I'm happy to help. Here is how the bonds are split into the non polar covalent, polar covalent, and the ionic bonds.
Nonpolar Covalent Bonds: If the electronegativity difference between two atoms is between 0.0 and 0.4, then the electrons are shared almost equally, resulting in a nonpolar covalent bond.
Polar Covalent Bonds: If the electronegativity difference is between 0.4 and 1.7, the electrons are shared unequally, resulting in a polar covalent bond. The atom with the higher electronegativity will attract the shared electrons more strongly.
Ionic Bonds: If the electronegativity difference is greater than 1.7, the electrons are transferred from one atom to another, resulting in an ionic bond. This typically occurs between a metal and a nonmetal.
Therefore, your statement that if the difference in electronegativity is 0.4-1.7 it is a covalent bond (specifically a polar covalent bond), and if it is above 1.7 it is an ionic bond, is indeed correct.
lol this is my first answer i wrote, hope it helped:)(1 vote)
Video transcript
- [Instructor]
Electronegativity is probably the most important concept to understand in organic chemistry. We're gonna use a definition
that Linus Pauling gives in his book, "The Nature
of the Chemical Bond". So Linus Pauling says
that electronegativity refers to the power of
an atom in a molecule to attract electrons to itself. So if I look at a molecule, I'm going to compare two
atoms in that molecule. I'm going to compare carbon to oxygen in terms of the electronegativity. And to do that, I need to
look over here in the right at the organic periodic table, which shows the elements
most commonly used in organic chemistry, and then in blue, it gives us the Pauling
scale for electronegativity. So Linus Pauling actually calculated electronegativity values for the elements and put them into the table, and that allows us to
compare different elements in terms of their electronegativities. For example, we are concerned with carbon, which has an electronegativity
value of 2.5, and we're going to compare that to oxygen, which has an electronegativity
value of 3.5. So oxygen is more
electronegative than carbon. And the definition tells us that if oxygen is more electronegative, oxygen has a greater power to
attract electrons to itself than carbon does. And so if you think about the electrons and the covalent bond
between carbon and oxygen that are shared, they're shared unequally, because oxygen is more electronegative. Oxygen's going to pull
those electrons in red closer to itself. And since electrons
are negatively charged, the oxygen's gonna get a little
bit more negative charge, and so it's going to have what we call a partial
negative charge on it. So partial negative, partial sign is a lowercase
Greek letter delta. And so the oxygen is partially negative. It's pulling the electrons
in red closer to itself. Another way to show the movement
of those electrons in red closer to the oxygen would
be this funny arrow here. So the arrow points in the
direction of the movement of the electrons in red. So carbon is losing some
of those electrons in red. Carbon is losing a little
bit of electron density. Carbon is losing a little
bit of negative charge. So carbon used to be neutral, but since it's losing a
little bit of negative charge, this carbon will end up being
partially positive like that. So the carbon is partially positive, and the oxygen is partially negative. That's a polarized situation, right? You have a little bit of
negative charge on one side, a little bit of positive
charge on the other side. So it's still a covalent bond, but it's a polarized covalent bond due to the differences
in electronegativities between those two atoms. Let's do a few more examples here where we show the differences
in electronegativity. So if I were thinking about a molecule that has two carbons in it, and I'm thinking about what
happens to the electrons in red, well, for this example, each carbon has the same value
for electronegativity, right? So the carbon in the
left has a value of 2.5. The carbon in the right
has a value of 2.5. That's a difference in
electronegativity of zero, which means that the electrons
in red aren't gonna move towards one carbon or
towards the other carbon. They're gonna stay in the middle, they're gonna be shared
between those two atoms. So this is a covalent bond, and there's no polarity
situation created here, since there's no difference
in electronegativity. So we call this a nonpolar
covalent bond, right? So this is a nonpolar
covalent bond, like that. Let's do another example. Let's compare carbon to hydrogen. So if I had a molecule and I have a bond between
carbon and hydrogen, and I want to know what
happens to the electrons in red between the carbon and the
hydrogen, we've seen that carbon has an electronegativity value of 2.5, and we go up here to hydrogen,
which has a value of 2.1, and so that's difference of 0.4. So there is a difference
in electronegativity between those two atoms, but
it's a very small difference. and so most textbooks
would consider the bond between carbon and hydrogen to still be a nonpolar covalent bond. All right, let's go ahead and put in the example
we did above, right. where we compared the electronegativies of carbon and oxygen, like that. When we looked up the
values, we saw that carbon had an electronegativity value of 2.5, and oxygen had a value of
3.5 for a difference of one. And that's enough to have a
polar covalent bond, right? This is a polar covalent bond between the carbon and the oxygen. So when we think about
the electrons in red, the electrons in red are
pulled closer to the oxygen, giving the oxygen a
partial negative charge, and since electron density is
moving away from the carbon, the carbon gets a partial positive charge. And so we can see that if your difference in electronegativity is one, it's considered to be
a polar covalent bond, and if your difference in
electronegativity is 0.4, that's considered to be
a nonpolar covalent bond. So somewhere in between
there must be the difference between non-polar covalent
bond and a polar covalent bond. And most textbooks will tell
you approximately somewhere in the 0.5 range. So if the difference in electronegativity is greater than 0.5, you
can go ahead and consider it to be mostly a polar covalent bond. If the difference in
electronegativity is less than 0.5, we would consider that to
be a nonpolar covalent bond. Now, I should point out that
we're using the Pauling scale for electronegativity here, and there are several different scales for electronegativity. So these numbers are not absolute. These are more relative differences, and it's the relative
difference in electronegativity that we care the most about. Let's do another example. Let's compare oxygen to hydrogen. So let's think about what
happens to the electrons between oxygen and hydrogen. So the electrons in red here. All right, so we've already seen the electronegativity values
for both of these atoms. Oxygen had a value of 3.5, and
hydrogen had a value of 2.1. So that's an electronegativity
difference of 1.4. So this is a polar covalent bond. Since oxygen is more
electronegative than hydrogen, the electrons in red are going
to move closer to the oxygen. so the oxygen's going to get
a partial negative charge, and the hydrogen's gonna get
a partial positive charge, like that.