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So in class we have learned London dispersion, dipole-dipole, ion-dipole and hydrogen bonding for intermolecular forces. Our teacher always uses covalent molecules as examples. So I was wondering which intermolecular forces ionic bonds have, if so, how are they formed?

Peter Zhu
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  • Ionic bonds are the product of Coulombic interactions within the ionic compound. Intermolecular forces means 'between molecules' and (unfortunately), in this case, extends to ion/dipoles. – LordStryker Oct 07 '15 at 21:23
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    It would be only natural to continue the series "dipole-dipole, ion-dipole" with ion-ion interaction, which is precisely the same as ionic bond. – Ivan Neretin Oct 07 '15 at 21:25

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Ions in ionic compounds are held together by electrostatic attractions, i.e. the idea that "opposite charges attract".

The strength of an electrostatic attraction is given by Coulomb's law:

$$F = \frac{1}{4\pi\varepsilon_0}\frac{q_1q_2}{r^2}$$

where $q_1$ and $q_2$ are the charges on the two ions and $r$ is the distance between them. In a completely ionic bond, $q_1$ and $q_2$ are multiples of the elementary charge, $e = 1.602 \times 10^{-19} \text{ C}$; however, no bond is completely ionic.

Community
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orthocresol
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  • But this doesn't answer the question..... – Peter Zhu Oct 07 '15 at 22:07
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    My first sentence answers your question. I just decided to expand a bit. The fact that opposite charges attract is a consequence of the electromagnetic force, one of the four fundamental interactions of the universe. – orthocresol Oct 07 '15 at 22:44
  • So do ionic molecules have intermolecular forces? – Peter Zhu Oct 08 '15 at 00:28
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    I would not say so. Ionic compounds do not exist as discrete molecules anyway, so the term intermolecular loses a bit of its appropriateness. If you talk about a single "molecule" of NaCl, then it should be an intramolecular force because these forces are what hold the constituent ions together. This is why textbooks will never write about the "intermolecular forces in ionic compounds". They will write: ionic compounds are a giant lattice of ions held together by electrostatic attraction. – orthocresol Oct 08 '15 at 07:07
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To me ionic bonding stand alone from both intramolecular force and intermolecular force. As it is a not interaction involving any molecules/atoms. Other forces such as ion-permanent dipole and ion-induced dipole would be intermolecular force, because those forces involved molecules. Although the fact is that all those 3 kind of bonds involving electrostatic force/electromagnetic force(force between charge particle/poles). It’s just generally ionic bonding stronger than ion-permanent dipole interaction, and ion-permanent dipole interaction stronger than ion-induced dipole interaction.

Aemon Zhou
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