# Can nonpolar molecules exhibit dipole-dipole forces?

Dipole-dipole forces occur when the positive part of a polar molecule is attracted to the negative part of a polar molecule. In a nonpolar molecule, there may still be polar bonds, it's just that the dipoles cancel each other out. So why can't there be dipole-dipole forces between nonpolar molecules with polar bonds? There are still positive and negative parts of the molecule, so there can be attractions between them.

For example, in $\ce{CO2}$, there are negative areas near the oxygens and positive areas near the carbon.

• Jan 4, 2016 at 0:20

Short answer: there are many electrostatic interactions between two non-polar molecules.

Beyond monopole (full charges) and permanent dipole moments (polar molecules), there is a full multipole expansion for the electrostatic potential around any molecule. (This is technically true for atoms and ions too, but higher-order terms are really only useful for molecules.)

These terms are important - the quadrupole-quadrupole interactions dictate the orientation of the benzene dimer and $\ce{CO2}$ dimer in your example.1

The problem is that most of these interactions die off very quickly. The quadrupole-quadrupole term is:1

$$E(r)=\frac{-\Theta_1\Theta_2}{4\pi\epsilon_0r^5}\times\Gamma(\theta_1,\theta_2,\phi)$$

So roughly $1/r^5$, compared to $1/r^3$ for dipole-dipole interactions, or $1/r^6$ for dispersion forces like induced-dipoles.

When such molecules are close, the quadrupole moments (and other multipole electrostatic terms) can dictate packing and distances, but are not as strong or as long-range as dipole-dipole or charge interactions.

• So nonpolar molecules with polar bonds would have higher melting and boiling points than nonpolar molecules with no polar bonds right? Dec 30, 2015 at 16:22
• @swenger There are a lot of things that go into melting points and boiling points (e.g., internal rotations, etc.) but if you had two hypothetically equivalent non-polar molecules and one had polar bonds (and thus quadrupole interactions) it should have higher forces and higher mp and bp, yes. Dec 30, 2015 at 17:11
• @Geoff Hutchison Can polar molecules like water exhibit induced dipole moment interactions? We know that water molecules have permanent dipole moment but are there any changes in the dipole moment due to polarizability so we have an extra interaction? May 18 at 14:46

In the case of non-polar molecules, dispersion forces or London forces are present between them. These forces are induced dipole - induced dipole interactions. As we know that in non-polar molecule, the whole molecule has zero dipole moment but bonds are polar.

When two non-polar molecules comes closer to each other. The negative part (electrons) of one molecule attract the positive part (nucleus) of another molecule. As a result, two dipoles are induced. Such dipoles are called induced dipoles and interaction is called induced dipole - induced dipole interactions.

Example - CO2 - CCl4 and He - Ne intractions

• This doesn't actually answer the question about whether there are dipole-dipole forces in molecules like $\ce{CO2}$ and if not, why.
– bon
Dec 30, 2015 at 13:17

Dipole-dipole interactions are electrostatic interactions between the permanent dipoles of different molecules. These interactions align the molecules to increase the attraction.

In order to form a dipole-dipole attraction, there should be a dipole moment for the considered molecule.

For an example: Water ($\ce{H2O}$)

It has a large permanent electric dipole moment. It's positive and negative charges are not centered at the same point; it behaves like a few equal and opposite charges separated by a small distance.

The permanent dipole in water is caused by oxygen's tendency to draw electrons to itself (i.e. oxygen is more electronegative than hydrogen). The 10 electrons of a water molecule are found more regularly near the oxygen atom's nucleus, which contains 8 protons. As a result, oxygen has a slight negative charge (δ-). Because oxygen is so electronegative, the electrons are found less regularly around the nucleus of the hydrogen atoms, which each only have one proton. As a result, hydrogen has a slight positive charge (δ+)

If we considered a NON POLAR molecule with POLAR BONDS as you mentioned; such as $\ce{CCl4}$ or $\ce{CO2}$

Molecules often contain polar bonds because of electronegativity differences but have no overall dipole moment if they are symmetrical. In the molecule tetrachloromethane ($\ce{CCl4}$), the chlorine atoms are more electronegative than the carbon atoms, and the electrons are drawn toward the chlorine atoms, creating dipoles. However, these carbon-chlorine dipoles cancel each other out because the molecular is symmetrical, and $\ce{CCl4}$ has no overall dipole movement.

Though $\ce{CO2}$ have polar bonds,it does not have a dipole moment, so it can not form dipole-dipole interactions.