Dipole Moment (Simplified) - Online Tutor, Practice Problems & Exam Prep

Dipole Moment (Simplified) Concept 1

Now before we can talk about dipole moments, we have to take a look at electronegativity. We're going to say it's the measurement of an element's ability to attract electrons to itself. So basically, the higher the electronegativity value of an element, the more it desires electrons near it. We're going to say in 1932, it was the American chemist, Linus Pauling, who proposed electronegativity values for the elements. I thought this was good to include because at this point we've heard a lot about chemists from Germany, Russia, and France. We don't usually hear too much about old-school chemists from the US. Here, we're going to say that the periodic trend of electronegativity is as follows: as we move from left to right across a period and go up a group, our electronegativity should increase. So electronegativity increases in this movement. And we're going to say as we head towards the top right, basically, our electronegativity is increasing. Now remember, we said that electronegativity is the element's ability to attract electrons to itself. The noble gases are perfect; they don't really want electrons. Of course, there are exceptions to this in the form of Krypton and Xenon. They exist in the sweet spot of group 18A where they can accommodate additional electrons to themselves to help make different types of Lewis dot structures. But what's most important in this graph is that fluorine is the most electronegative. An easy way to remember that is in college; we're all looking for that perfect 4.0 GPA. Fluorine has a 4.0 in terms of electronegativity. So as we head towards fluorine, things become more and more electronegative. Alright. So this is the basic trend that you need to keep in mind when talking about electronegativity as a periodic trend.

Dipole Moment (Simplified) Example 1

Here it says, which of the following represents the most electronegative alkaline earth metal? Alright. So this question is actually easier than it appears. You don't need to look at the electronegative values. You don't even need to remember the pattern because there's only one alkaline earth metal presented here. The only element that's an alkaline earth metal is beryllium. So the answer here is d. But remember, the general trend is as we head to the top right corner of the periodic table, our electronegativity will increase. So just keep in mind this general periodic trend for electronegativity.

Dipole Moment (Simplified) Concept 2

Now a dipole moment is the polarity that arises when elements in a bond have a significant difference in their electronegativities. Polarity is just the unequal sharing of electrons between these bonding atoms, and a difference in electronegativity greater than 0.4 is considered significant. The difference in electronegativity, which is ΔEN=the higher electronegativity value minus the lower one. If you have polarity in a bond, you have a dipole moment. This is illustrated by a dipole arrow that always points towards the more electronegative element. If you were to calculate the difference between fluorine and carbon, you would see the difference is greater than 0.4. So it has a dipole moment, so we use a dipole arrow. Here, the end that is more electronegative gets a partial charge of δ-. The end that is less electronegative is δ+. And if you look at this dipole arrow, you're going to see circling this end. It looks like a positive sign, which makes sense because this end is partially positive. So remember, if your difference in electronegativity is significant, you show a dipole arrow. That dipole arrow is representative of the polarity within that bond. The end where the dipole arrow is pointing will be partially negative, and the other end will be partially positive.

Dipole Moment (Simplified) Example 2

Calculate the difference in electronegativity values between carbon and fluorine. So here we still have the image of carbon connected to fluorine. We have the presence of a dipole arrow because the difference between them should be greater than 0.4. Now, let's calculate what exactly that value is. On our periodic table, the electronegativity value of fluorine is 4.0, and that of carbon is 2.5. So here we're going to say the difference in electronegativity Δχ=4.0-2.5. When we do that, we get a difference of 1.5, which is option d. And again, since the difference exceeds 0.4, we know that this compound has a dipole moment. And as a result, we use a dipole arrow to illustrate that. Remember, the dipole arrow itself points towards the more electronegative element within the bond.

Arrange the following molecules in order of decreasing dipole moment.

H–I           H–F         H–Br         H–Cl

• A. H–Cl >H–I > H–Br > H–F
• B. H–Br >H–Cl > H–F > H–I
• C. H–F >H–Cl > H–Br > H–I
• D. H–I >H–Cl > H–Br > H–F

Dipole Moment (Simplified) Concept 3

We're going to say that the difference in electronegativities between two elements can determine the type of chemical bond present. We're going to say the greater the difference in electronegativity, then the greater the polarity of the bond. Now, if we take a look, we can see here that we have differences in electronegativities. If the difference is 0, that must mean they both have the same electronegativity value. We classify this as a pure covalent bond. A great example is two bromines bonded together. They're sharing these electrons here in the center and they're sharing them equally, so you'll have these equal arrows between them. Here, this shading represents their electron cloud. They're equal in size because again, their electronegativity values are the same. They're sharing them perfectly. Now, once you start getting a little difference in electronegativity, we go into what we call a nonpolar covalent 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 its electronegativity value was a little bit higher than hydrogen's. It's 2.5 versus hydrogen's 2.1. We still have arrows, but notice that this arrow is slightly larger because the electrons belong a little more towards carbon's side. Now, what you need to realize here is that pure covalent is when there is no difference in electronegativity, but it is also classified as being nonpolar. Now, intermediate is when the difference is between 0.5 and 1.7. Here, we classify this as a polar covalent bond. If we take a look here, we have chlorine and hydrogen. Remember, once we are greater than 0.4 difference in electronegativity, that's significant. That means we're going to be polar and with a polarity involved, we have dipole arrows. The dipole arrow always points towards the more electronegative element. It's pointing towards chlorine, which is more electronegative than hydrogen. Remember, chlorine is 3.0. Hydrogen is just 2.1. With the dipole arrow, we have charges involved. In this case, partial charges. Here, chlorine will be partially negative. Hydrogen will be partially positive. Finally, if it's larger than 1.7, then 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 cation ion is formed because sodium actually hands over its electron to chlorine. Now here, it also has a dipole arrow, but it's much larger because the polarity is even greater. Here, this is another difference: that whereas in polar covalent 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 more electronegative element. So just remember, the greater your difference in electronegativity, the greater the polarity of the bond. These differences in polarity help to classify different types of chemical bonds present.

Dipole Moment (Simplified) Example 3

For those listed below, which has the most polar bond? Remember, the most polar bond would be attached to the greatest difference in electronegativity. Looking at the electronegativity chart, we'd see that sulfur is 2.5, selenium is 2.4. We'd see here 2.5, hydrogen would be 2.1. Chlorine here would be 3.0 and here we'd have fluorine at 4.0. Sulfur again is 2.5 and fluorine is 4.0. This would be 2.5 and this would be 3.5. Remember difference in electronegativity is the larger electronegativity value minus the smaller one. Here if we did that it'd be 4-2.5 which would give us 1.5. We'd see that option d gives us the biggest difference in electronegativity which would translate into the most polar bond present. So just remember, most polar bond means biggest difference in electronegativities.

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

Arrange the following elements in order of decreasing electronegativity: P, Na, N, Al

• A. P > Na > N > Al
• B. b) N > P > Na > Al
• C. Na > Al > P > N
• D. N > P > Al > Na
• E. P > N > Na > Al

Between which two elements is the difference in electronegativity the greatest?

• A. C and Si
• B. Li and I
• C. Na and P
• D. K and F
• E. Br and Cl

Which of the following correctly identifies the chemical bond between two bromine atoms?

• A. Polar Covalent
• B. Pure Covalent
• C. Nonpolar Covalent
• D. Ionic

Here’s what students ask on this topic:

What is electronegativity and how does it affect dipole moments?

Electronegativity is a measure of an element's ability to attract electrons to itself. It was proposed by Linus Pauling and increases across a period and up a group in the periodic table, peaking at fluorine (4.0). A dipole moment arises when there is a significant difference in electronegativity between two bonded atoms (greater than 0.4). This difference causes an unequal sharing of electrons, leading to polarity in the bond. The more electronegative atom attracts the shared electrons more strongly, resulting in a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the less electronegative atom. The dipole moment is represented by a dipole arrow pointing towards the more electronegative element.

How do you calculate the difference in electronegativity between two elements?

The difference in electronegativity (ΔEN) between two elements is calculated by subtracting the electronegativity value of the less electronegative element from that of the more electronegative element. The formula is:

$\mathrm{\Delta EN}=\mathrm{EN}$_higher-EN_lower

If the difference is greater than 0.4, the bond is considered polar, and a dipole moment is present. For example, the electronegativity of fluorine (F) is 4.0, and that of carbon (C) is 2.5. The difference is:

$4.0-2.5=1.5$

This indicates a polar covalent bond with a dipole moment.

What is the significance of a dipole moment in a chemical bond?

A dipole moment in a chemical bond indicates the presence of polarity due to an unequal sharing of electrons between two atoms with different electronegativities. The significance of a dipole moment includes:

• Polarity: It shows that the bond is polar, with one end being partially negative (δ-) and the other partially positive (δ+).
• Intermolecular Forces: Polar molecules with dipole moments can interact through dipole-dipole interactions, affecting properties like boiling and melting points.
• Solubility: Polar molecules tend to dissolve well in polar solvents (like water), while nonpolar molecules dissolve in nonpolar solvents.
• Reactivity: The presence of a dipole moment can influence the chemical reactivity and interactions of the molecule.

How does the difference in electronegativity classify different types of chemical bonds?

The difference in electronegativity (ΔEN) between two bonded atoms classifies the type of chemical bond:

• Pure Covalent Bond: ΔEN = 0. Both atoms have the same electronegativity, sharing electrons equally (e.g., Br₂).
• Nonpolar Covalent Bond: ΔEN = 0.1-0.4. The difference is small, resulting in nearly equal sharing of electrons (e.g., C-H bond).
• Polar Covalent Bond: ΔEN = 0.5-1.7. The difference is significant, leading to unequal sharing of electrons and a dipole moment (e.g., H-Cl bond).
• Ionic Bond: ΔEN > 1.7. The difference is large, causing one atom to transfer electrons to the other, forming ions (e.g., NaCl).

The greater the ΔEN, the greater the bond's polarity, influencing the molecule's properties and interactions.

Why is fluorine considered the most electronegative element?

Fluorine is considered the most electronegative element with an electronegativity value of 4.0. This is because fluorine has a high effective nuclear charge and a small atomic radius, allowing it to attract electrons very strongly. Its position in the periodic table (top right) also contributes to its high electronegativity. Fluorine's strong ability to attract electrons makes it highly reactive and a key element in forming polar bonds with significant dipole moments. This high electronegativity is a fundamental concept in understanding chemical bonding and molecular interactions.