General Chemistry

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11. Bonding & Molecular Structure

Dipole arrows are used anytime a molecule possesses a dipole moment, which happens when a molecule is polar. 

Dipole Moments & Arrows
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concept

Dipole Moment

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to understand the dipole moment found within either a chemical bond or chemical compound. We first need to revisit electro negativity. Now recall electro negativity, abbreviated as E N. Is a measurement of an element's ability to attract electrons to itself. And the periodic trend that you need to remember is that electro negativity increases, moving from left to right across a period or row and up a group. So if we take a look here in terms of this periodic table, we'd say that we can see that the non metals, those in blue have a higher electro negative value, with flooring being the most electro negative. Now recall that noble gasses are perfect. So we tend not to talk about their electro negativity ease, but because Krypton and xenon are lowered down and have larger shells involved, they sometimes can have electro negative values associated with themselves. Krypton being three point oh and Xenon being 2.6 here, most of the seventh row is comprised of synthetically formed metals. So because they're so unstable, we don't give them electro negative values. And realize that over here in the bottom left corner we have francie um which has the lowest electro negative value. So just remember as we start talking about dipole moments, you need to remember that it's related to the electro negative values of these different elements. So click on the next video and let's start talking about dipole moments

Electronegativity increases moving from left to right and going up a group.

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concept

Dipole Moment

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now, a dipole moment is the polarity that arises when elements in a bond have a significant difference in their electoral negativity. Not polarity is just the unequal sharing of electrons between these bonding atoms at a difference in electro negativity, greater than four is considered significant now. Difference in electro negativity, which is Delta e n equals the higher electro negativity value minus the lower white. Now, if you have polarity in a bond, you have a dipole moment. This is illustrated by a die poll arrow that always points towards the Mawr electro negative element. If you were to calculate the difference between flooring and carbon, you would see the difference is greater than 0.4. So it has a dipole moment. So we use a depot era here. The end that is more electoral negative gets a partial charge of Delta Negative. The end that is mawr less electro negative. Is Delta positive? If you look at this select type own arrow, you're going to see circling this end, it looks like a positive sign which meat makes sense because this end is partially positive. So remember, if you're difference in electro negativity is significant, you show a depot era. That diaper arrow is representative of the polarity. Within that bond, the end where the diaper arrow is pointing will be partially negative, and the other end will be partially positive.

Dipole arrow is representative of bond polarity between 2 elements and points towards a more EN element.

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example

Dipole Moment Example 1

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we're going to say dipole moment is the polarity that arises when elements in a bond have a significant difference in their electoral negativity is not polarity itself. Is the unequal sharing of electrons between bonding Adams on We're gonna say a difference in electro negativity greater than 0.4 is considered significant now difference. Electro negativity abbreviated as Delta e n equals the larger or higher electro negativity value minus the smaller or lower electro negativity value, we're going to say the dipole. The type of moment is illustrated by dipole arrow that points towards the mawr electro negative value or element. So here we have carbon and we have flooring. If we look at this example, it says, calculate the difference in electro negativity. These values between carbon and flooring while carbon has an electoral negativity value of 2.5 and flooring is four point out. So Delta e n equals the larger value of 4.0, minus a smaller value of 2.5, so they're difference would be 1.5, which would give us option D. The fact that the electro negative negativity value is greater than 0. means that this bond is a polar bond and therefore would have a dipole moment. And a dipole moment means we have to use this die poll arrow. So that's how things are connected together. So if you're ever looking between two elements and you're trying to determine if the bond is polar and therefore has a dipole moment, you look at their difference and electro negativity one greater than 10.4 would mean that bond is polar and requires a dipole moment arrow. So again, because flooring is more electoral negative, the arrow would point towards it. Carbon is mawr is less electro negative mawr electoral positive. So if you think about it, this end here kind of looks like a positive sign if you were to circle it, and that's why it's on near carbon. So just keep this in mind when looking at the chemical bomb between two elements to determine if it has a dipole moment or not.
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concept

Dipole Moment

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we're going to say that the difference and electro negativity ease between two elements can determine the type of chemical bond present we're going to say the greater the difference in electoral negativity in the greater the polarity of the bond. Now, if we take a look, we can see here that we have differences and electro negativity ease. If the difference is zero, that must mean they both have the same electro negativity value. We classify this as a pure Covalin Bond. Great example is too, bro means bonded together. They're sharing these electrons here in the center, and they're sharing them equally. So you have these equal arrows between them. Here. This shading represents their electron cloud their equal in size because again they're electro negative. Values are the same. They're sharing them perfectly. Now, once you start getting a little bit difference in electro negativity, we go into what we call a non polar Covalin bond. Here it has a difference between 0.1 and 0.4. If we take a look here. Carbon is slightly bigger in terms of its electron cloud because it's electro negative. Value is a little bit higher than hydrogen. It's 2.5 versus hydrogen is 2.1. We still have arrows, but notice that this arrow is slightly larger because the electrons belong a little bit more towards carbon side. Now, what you need to realize here is that pure Covalin is when there is no difference in electro negativity. But it is also classified as being non polar. Now, intermediate is when the differences between 0.5 and 1.7. Here we classify this as a polar Covalin bond. If we take a look here, we have chlorine and hydrogen, Remember, once were greater than 0.4 difference in electro negativity. That's significant. That means we're gonna be polar and with a polarity involved, we have dipole arrows. The dipole arrow always points towards theme or electro negative element. It's pointing towards cart on chlorine, which is more electro negative than hydrogen. Remember, chlorine is 30 Hydrogen is just 2.1. With the depo era. We have charges involved in this case, partial charges here. Corn will be partially negative. Hydrogen will be partially positive. Finally, if it's larger than 1.7 than it is an Ionic bond. Remember, Ionic bonds are bonds between a positive ion and a negative ion here. The difference is so large that the cat eye on his form because sodium actually hands over its electron to chlorine. Now here it also has a depot arrow. But it's much larger because the polarity is even greater here. This is another difference. Here is that whereas in polar Covalin we have partial charges in Ionic we have full charges, so this is fully negative and this is fully positive. And again, the arrow points towards the mawr electro negative element. So just remember the greater difference in electro negativity, the greater the polarity of the bond. These differences in polarity helped to classify different types of chemical bonds present.

Differences in EN between bonds help us classify the different types of bonds possible.

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example

Dipole Moment Example 2

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for those listed below, which has the most polar bond. Remember, the most polar bond would be attached to the greatest difference and electro negativity. Looking at the electoral negativity is chart. We'd see that sulfur is 2.5. Selenium is 2.4. We'd see here to five. Hydrogen would be to one chlorine. Here would be three point. Oh, and here we have flooring at four point out sulfur again is to five and four inches. 40 This would be 2.5, and this would be 3.5. Remember, difference in electro negativity is the larger electro negativity value minus a smaller one. Here. If we did that before minus 2.5, which would give us 1.5. We see that option D gives us the biggest difference in electro negativity, which would translate into the most polar bond present. So just remember, most polar bond means biggest difference in electro negativity is
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Problem

Which of the following correctly identifies the chemical bond between a carbon and oxygen atom?

a) Polar Covalent

b) Pure Covalent

c) Nonpolar 

d) Ionic

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