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

Electronegativity measures an element's ability to attract electrons, increasing from left to right across a period and up a group in the periodic table. A dipole moment arises when there is a significant difference in electronegativities (ΔEN > 0.4), indicating polarity in a bond. Bonds are classified as pure covalent (ΔEN = 0), nonpolar covalent (0.1 < ΔEN < 0.4), polar covalent (0.4 < ΔEN < 1.7), or ionic (ΔEN > 1.7). The dipole arrow points toward the more electronegative element, indicating partial charges in polar and ionic bonds.

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 electronegativity value an element has, 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, from Russia, and from 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 we're moving from left to right across a period and going 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 8A where they could potentially accommodate additional electrons to themselves to help make different types of Lewis dot structures. But what's most important in this description 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 is 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 electronegativity 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, equals 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, and we use a dipole arrow. Here, the end that is more electronegative gets a partial charge of Δ-, and the end that is less electronegative is Δ+. When 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.

Δ E N = higher electronegativity value − lower electronegativity value

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 difference in electronegativity equals the higher electronegativity value, in this case 4.0, minus the smaller one of 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.

difference = higher electronegativity value 4.0 - smaller electronegativity value 2.5 = 1.5

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 bit 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 here is 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 electronegativities chart, we'd see that sulfur is 2.5, selenium is 2.4. 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, the difference in electronegativity is the larger electronegativity value minus the smaller one. Here, if we did that, it'd be 4−2.5=1.5 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, the most polar bond means the 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

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

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 increases from left to right across a period and up a group in the periodic table. A dipole moment arises when there is a significant difference in electronegativities (ΔEN > 0.4) between two bonded atoms. This difference causes an unequal sharing of electrons, leading to polarity in the bond. The dipole moment is represented by a dipole arrow pointing towards the more electronegative element, indicating partial charges: δ- for the more electronegative atom and δ+ for the less electronegative atom.

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:

$\mathrm{\Delta EN}=\mathrm{EN}{\mathrm{higher}}_{}-\mathrm{EN}{\mathrm{lower}}_{}$

If ΔEN is greater than 0.4, the bond is considered polar, and a dipole moment is present.

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

A dipole arrow in a chemical bond indicates the direction of electron density shift due to differences in electronegativity between the bonded atoms. The arrow points towards the more electronegative element, which attracts electrons more strongly. The tail of the arrow, often marked with a plus sign, indicates the less electronegative element, which has a partial positive charge (δ+). The head of the arrow points to the more electronegative element, which has a partial negative charge (δ-). This visual representation helps in understanding the polarity and distribution of charges within the molecule.

What are the different types of chemical bonds based on electronegativity differences?

Chemical bonds are classified based on the difference in electronegativity (ΔEN) between the bonded atoms:

• Pure Covalent Bond: ΔEN = 0, equal sharing of electrons (e.g., Br₂).
• Nonpolar Covalent Bond: 0 < ΔEN ≤ 0.4, nearly equal sharing of electrons (e.g., C-H bond).
• Polar Covalent Bond: 0.4 < ΔEN ≤ 1.7, unequal sharing of electrons, resulting in partial charges (e.g., H-Cl bond).
• Ionic Bond: ΔEN > 1.7, complete transfer of electrons, resulting in full charges (e.g., NaCl).

The greater the ΔEN, the more polar the bond.

Why is fluorine considered the most electronegative element?

Fluorine is considered the most electronegative element because it has the highest ability to attract electrons towards itself. This is due to its small atomic size and high nuclear charge, which allows it to exert a strong pull on electrons. In the periodic table, electronegativity increases from left to right across a period and up a group, making fluorine, located at the top right (excluding noble gases), the element with the highest electronegativity value of 4.0. This high electronegativity makes fluorine highly reactive and a strong oxidizing agent.