Ion–dipole forces occur between ions and polar molecules. The relative strength of these forces can be understood in terms of Coulomb's law, which tells us that the electrostatic attraction between ion and dipole is directly related to the magnitudes of the ion charge and the dipole and inversely related to the distance between them. Created by Sal Khan.
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- Ion is dealing with a whole atom & dipole is dealing with charges being separated in the atom. Right ?(3 votes)
- Ions were once neutral atoms which either gained or lost a number of electrons which now results in imbalance between the number of negative electrons and positive protons. Technically ions and atoms are categorized differently. Ions engage in ionic bonding where positive ions (cations) are attracted to negative ions (anions).
A dipole exists in a molecule which engages in covalent bonding, but one side of the molecule has more electronegativity than the other side. Basically certain atoms on side of a molecule like electrons more so than other atoms. Having a lot of electrons gives the side with more electronegativity a partial negative charge and the side with an absence of electrons gets a partial positive charge. This creates a polar molecule with a negative and a positive pole.
Ions and polar molecules are both polar and so can interact with each other which is why ionic solids dissolve in polar liquids.
Hope that helps.(8 votes)
- How exactly do we recognize/tell the difference between dipole dipole forces and ion dipole forces?(2 votes)
- Dipole-dipole interactions occur between molecules who have only partial electric charges. Ion-dipole occurs between particles where one has a partial electric charge (the dipole) and the other has a full charge (the ion).
Hope that helps.(7 votes)
- I have a question about the role that ionic radius plays in ion-dipole attraction.
I understand why a higher, net-positive charge would be attracted more to the negative dipole end of a molecule.
But why does a smaller ionic radius increase attraction?
The only hypothesis I could come up with was that -
Smaller cations experience higher nucleus repulsion
Am I on the right path here?(2 votes)
- Look up Coulomb's Law which describes the force of attraction between charged particles. In it the charges of the particles are directly proportional the force of attraction (or repulsion), and that force is inversely proportional to the square of the distance between the charges.
The greater the magnitude of the charges the greater the strength of the electric fields being emitted from the ions. The smaller the ionic radii of the ions, the shorter the distance the electric fields have to travel to reach to opposite ions and hence the stronger the electric field felt by the ions.
Hope that helps.(3 votes)
- So would ion-dipole interactions be considered generally stronger than dipole-dipole forces, or does it depend on the charge of the ion/strength of the dipole?(2 votes)
- [Instructor] Let's talk a little bit about ion-dipole forces. And before we think about how ions and dipoles might interact, let's just remind ourselves what the difference is between ions and dipoles. And I encourage you to pause this video and try to refresh your own memory before we refresh our memories together. All right, now let's first think about ions. Ions are atoms or molecules that have a net charge. So for example, when chlorine gains an electron and becomes the chloride ion, it's an ion because it now has a net negative charge. Similarly, when sodium loses an electron, it now has a net positive charge. So this is the sodium ion. Now what's the difference between that and a dipole? Well, generally speaking when we're talking about dipoles, we're not talking about something that has necessarily a net charge, we're talking about something where the charge is separated on different ends of the molecule, that you have a partially positive end and you have a partial negative end, that there is a molecular dipole moment. And a good example of a molecule that is a dipole or has a dipole moment at a molecular level is water. Water is a very polar molecule. We've talked about this many times. You have your oxygen which is quite electronegative, covalently bonded to two hydrogens, and those are really polar covalent bonds because the oxygen's so much more electronegative that it hogs the electrons, it's selfish of the electrons. And since the electrons spend more time around the oxygen than around the hydrogen, you have a partial negative charge at this end of the molecule and you have partial positive charges at the other end of the molecules. And we describe this when we talked about hydrogen bonding where the partial negative end of one water molecule would be attracted to the partial positive end of another water molecule. But, as we've talked about, hydrogen bonds, which are an intermolecular force are just a special case of dipole forces. Things that are able to form hydrogen bonds just have a very strong dipole moment, because you have hydrogen bonded to an oxygen, a nitrogen, and a fluorine, that is quite electronegative. So now that we know the difference between ions and dipoles, how might they interact? Well you might guess Coulomb forces are at play. The partial negative end of a dipole would be attracted to a positively charged ion. And I have prearranged these water molecules so that you have the partial negative end is facing towards this sodium positive ion. And so what I'm drawing right over here, these are ion-dipole forces. Similarly, if you have a chloride anion, or a negative ion, well then the partially positive ends of the dipoles are going to be attracted, and so water might arrange itself in this way where the partial positive ends, the ends with the hydrogen, are facing the chlorine. And this is one of the reasons why it's so easy to dissolve sodium chloride, to dissolve table salt in water. Those ions are able to separate and be attracted to the water molecules which are polar, which have molecular dipoles. Now, if I were to ask you what's gonna dictate the strength of the ion-dipole forces, think about that. Pause this video, and what do you think is going to matter? Well, as you can imagine, these are Coulomb forces. So the strength of the charges matter. So you're gonna have a stronger ion-dipole force if you have stronger charges on the ions. So instead of a sodium with a positive one charge, if you had a calcium ion that had a positive two charge, then the partially negative ends of the water molecules would be even more strongly attracted. You would have stronger ion-dipole forces. Similarly if you have stronger dipole moments, that will also make the ion-dipole forces stronger, or vice versa. If you had a molecule that had a weaker dipole moment, you're not going to have as strong ion-dipole forces. Coulomb forces are inversely proportional to the distance between the charges. So you're also going to have stronger ion-dipole forces the closer that these things get to each other. But to some degree that's true of a lot of the intermolecular forces we've talked about, because on some level they are all Coulomb forces.