Dipole Moment: Videos & Practice Problems

Electronegativity (EN) is a measure of an atom's ability to attract electrons towards itself, increasing from left to right across the periodic table and up a group. Understanding electronegativity is crucial when examining dipole moments, which occur when there is a significant difference in electronegativity between atoms in a bond, leading to unequal electron sharing. A difference in electronegativity greater than $0.4$ is significant, resulting in a polar bond with a dipole moment. This is depicted by a dipole arrow pointing towards the more electronegative atom, indicating a partial negative charge (δ-) at that end and a partial positive charge (δ+) at the other. The type of bond—nonpolar covalent, polar covalent, or ionic—depends on the difference in electronegativity values. Nonpolar covalent bonds have a difference of $0$ to $0.4$, polar covalent bonds range from $0.5$ to $1.7$, and a difference larger than $1.7$ indicates an ionic bond, where electrons are transferred, and full charges develop, rather than partial charges seen in polar covalent bonds.

Dipole Moment

To understand the dipole moment found within either a chemical bond or chemical compound, we first need to revisit electronegativity. Now recall electronegativity, abbreviated as EN, is a measurement of an element's ability to attract electrons to itself. And the periodic trend that we need to remember is that electronegativity 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 nonmetals, those in blue, have a higher electronegative value, with fluorine being the most electronegative. Now recall that noble gases are perfect, so we tend not to talk about their electronegativities. But because Krypton and xenon are lowered down and have larger shells involved, they sometimes can have electronegative values associated with themselves. Krypton being 3.0 and xenon being 2.6.

Here most of the 7th row is comprised of synthetically formed metals. So because they're so unstable, we don't give them electronegative values. And realize that over here in the bottom left corner we have francium which has the lowest electronegative value. So just remember, as we start talking about dipole moments, you need to remember that it's related to the electronegative values of these different elements.

So click on the next video and let's start talking about dipole moments.

Dipole Moment

Now a dipole moment is the polarity that arises when elements in a bond have a significant difference in their electronegativities. Now polarity is just the unequal sharing of electrons between these bonding atoms and a difference in electronegativity greater than 0.4 is considered significant. Now difference in electronegativity which is delta EN equals the higher electronegativity value minus the lower one.

Now 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 flooring 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 delta negative. The end that is more or less electronegative is delta positive.

If you look at the select 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 Example 1

We're going to say dipole moment is the polarity that arises when elements in a bond have a significant difference in their electronegativities. Now polarity itself is the unequal sharing of electrons between bonding atoms and we're going to say a difference in electronegativity greater than 0.4 is considered significant. Now difference in electronegativity, abbreviated as ΔEN, equals the larger or higher electronegativity value minus the smaller or lower electronegativity value.

We're going to say the dipole. The dipole moment is illustrated by dipole arrow that points towards the more electronegative value or element. So here we have carbon and we have fluorine. If we look at this example, it says calculate the difference in electronegativities values between carbon and fluorine. While carbon has an electronegativity value of 2.5 and fluorine is 4.0, so ΔEN equals the larger value of 4.0 minus a smaller value of 2.5. So their difference would be 1.5 which would give us option D.

The fact that the electronegativity negativity value is greater than 0.4 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 dipole 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 in electronegativity. One greater than 0.4 would mean that bond is polar and requires a dipole moment arrow.

So again, because fluorine is more electronegative, the arrow would point towards it. Carbon is more is less electronegative, more electropositive. 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 O. I'll just keep this in mind when looking at the chemical bond between two elements to determine if it has a dipole moment or not.

Arrange the following molecules in order of decreasing dipole moment.
H–I H–F H–Br H–Cl

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

Answer: (B)

Dipole Moment

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 than 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 2 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 bit 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 is a little bit higher than hydrogens. It's 2.5 versus hydrogens 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 covalent is when there's no difference in electronegativity, but it is also classified as being nonpolar. Now intermediate is when the differences between oh 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 CART on chlorine which is more electronegative than hydrogen. Remember chlorine is 3.0, Hydrogen is just 2.1 with a 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 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 we're as 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 Example 2

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's 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 a smaller one. Here if we did that before -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

Answer: (A)

Here’s what students ask on this topic:

What is a dipole moment?

A dipole moment is a measure of the separation of positive and negative electrical charges within a molecule. It's a vector quantity, which means it has both magnitude and direction. The dipole moment arises due to the difference in electronegativity between two atoms bonded together; the more electronegative atom pulls the shared electrons closer to itself, creating a partial negative charge, while the less electronegative atom acquires a partial positive charge.

The magnitude of the dipole moment is measured in Debye units and is calculated by multiplying the amount of charge separation by the distance between the charges. A molecule with a higher dipole moment is generally more polar, meaning it has a stronger charge imbalance, which affects its physical properties and the way it interacts with other molecules. For example, molecules with significant dipole moments tend to have higher boiling points and are more likely to be soluble in polar solvents like water.

How do you calculate dipole moment?

To calculate the dipole moment, you need to consider both the magnitude of the charges involved and the distance between them. The dipole moment (μ) is the product of the charge (Q) on either end of the dipole and the distance (r) between the charges:

μ = Q × r

The charge is usually measured in coulombs (C), and the distance in meters (m), which gives the dipole moment in coulomb-meters (C·m). However, in chemistry, the charges are often in terms of the elementary charge (e), and the distance in angstroms (Å) or picometers (pm), so the dipole moment may be given in Debye units (D).

1 Debye is approximately 3.33564 × 10 - 30 C·m . To convert from the product of elementary charge and distance in Å to Debye, you can use the conversion factor:

1 D = 1 3.33564 × 10 - 30 C·m e · Å

Keep in mind that the direction of the dipole moment vector is from the negative charge to the positive charge.

What is bond polarity?

Bond polarity refers to the distribution of electrical charge over the atoms joined by the bond. In a covalent bond, where two atoms share a pair of electrons, the electrons are not always shared equally. This can happen when the two atoms have different electronegativities, which is a measure of how strongly an atom can attract electrons to itself.

When one atom has a higher electronegativity than the other, it will attract the shared electrons more strongly, causing a partial negative charge (δ^-) to develop on the more electronegative atom, and a partial positive charge (δ⁺) on the less electronegative atom. This creates a dipole, which is a pair of equal and oppositely charged or magnetized poles separated by a distance.

A bond between two atoms with identical or similar electronegativity (like H-H or Cl-Cl) is nonpolar, meaning the electrons are shared equally, and there is no permanent charge difference between the atoms. In contrast, a bond between atoms with different electronegativities (like H-Cl) is polar, with a positive end and a negative end, much like a magnet.

How do you determine bond polarity?

To determine bond polarity, you need to consider the electronegativity of the atoms involved in the bond. Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. Here's a step-by-step process:

1. Identify the Atoms: Look at the two atoms that form the bond.
2. Electronegativity Values: Find the electronegativity values for each atom. These values are typically found on a chart or in a chemistry textbook.
3. Calculate the Difference: Subtract the smaller electronegativity value from the larger one to determine the difference in electronegativity between the two atoms.
4. Determine Polarity: If the difference is:

• 0, the bond is nonpolar covalent, meaning the electrons are shared equally.
• Less than 0.5, the bond is generally considered to be mostly nonpolar covalent, but with slight polarity.
• Between 0.5 and 1.9, the bond is polar covalent, meaning the electrons are shared unequally, and the atom with the higher electronegativity will have a partial negative charge, while the other atom will have a partial positive charge.
• 2.0 or greater, the bond is usually considered

What determines the polarity of a bond?

The polarity of a bond is determined by the difference in electronegativity between the two atoms forming the bond. Electronegativity is a measure of how strongly an atom attracts electrons in a chemical bond. When two atoms with different electronegativities form a bond, the electrons are not shared equally. The atom with the higher electronegativity will attract the shared electrons more strongly, acquiring a partial negative charge, while the other atom will have a partial positive charge. This creates a dipole, with one end being slightly negative and the other slightly positive, resulting in a polar bond.

If the difference in electronegativity between the two atoms is significant (generally a difference greater than 0.5 on the Pauling scale), the bond is considered polar. If the electronegativity difference is very small or zero, as in the case of two identical atoms, the bond is nonpolar because the electrons are equally shared. The greater the difference in electronegativity, the more polar the bond will be.