How are dipole - dipole forces created?
1 Answer
Dipole-dipole forces are present when there is an asymmetrical probability density where negative partial charges tend to be on a particular side with a positive partial charge on the opposite side.
Explanation:
There are mainly two types of dipole-dipole interactions between molecules:
- instantaneous dipole-induced dipole (id-id)
- permanent dipole-permanent dipole (pd-pd).
In pd-pd, electrons are more attracted towards sites with more electronegative atoms. As such, an asymmetrical probability density is created where negative partial charges tend to be on a particular side with a positive partial charge on the opposite side.
Pd-pd interactions occur in polar molecules.
On the other hand, id-id is due to the random movement of electrons in their (overlapping) orbitals. At any point in time, it is unlikely that electrons will be equally distributed. Sites with instantaneously more electrons will have a negative dipole while sites with fewer electrons will have a positive dipole. These dipoles created in one molecule will induce other sets of dipoles in other molecules and hence the name "induced dipole".
Id-id is found in all atoms and molecules, especially in larger ones.
