0
$\begingroup$

This question already has an answer here:

Molecules have IMAFs that determine the melting and boiling points. What about with ionic substances? What keeps the different compounds together? Do they experience IMAFs? I've heard that it's the ionic bond itself, but doesn't the bond remain after melting, and even if it doesn't then how come covalent bonds don't cause the boiling and melting points in molecules? Sorry for all the questions, main ones are in the title.

$\endgroup$

marked as duplicate by Todd Minehardt, Jon Custer, ringo, bon, Klaus-Dieter Warzecha Apr 25 '16 at 7:36

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 3
    $\begingroup$ What are IMAFs? $\endgroup$ – bon Apr 24 '16 at 21:27
  • $\begingroup$ Do you know what an ionic compound looks like? Do you think, for example, NaCl is just a collection of NaCl molecules floating around held together by so-called "intermolecular" forces? $\endgroup$ – orthocresol Apr 24 '16 at 21:38
  • 1
    $\begingroup$ Obviously ionic compounds aren't even molecules so they can't experience IMAFs, the question was getting at what holds the particles together so that they're a lattice that doesn't want them to be liquids or gases? $\endgroup$ – John Apr 24 '16 at 21:45
  • 2
    $\begingroup$ The particles are positively and negatively charged. Positive attracts negative. $\endgroup$ – orthocresol Apr 24 '16 at 21:47
  • $\begingroup$ The total binding energy in $\ce{NaCl}$ is more than the sum of the binding energy of all the "pairs" of ions. It is because all the ions are interacting. See the wikipedia article on the Madelung constant. en.wikipedia.org/wiki/Madelung_constant $\endgroup$ – MaxW Apr 24 '16 at 22:24
1
$\begingroup$

Molecules have IMAFs that determine the melting and boiling points. What about with ionic substances? What keeps the different compounds together? Do they experience IMAFs?

The problem is that you are trying to apply a paradigm that was developed for covalent compounds (the distinction between covalent bonds and intermolecular forces) to ionic compounds. They don't play by the same rules. In an ionic compound, all the ions are held together by electrostatic forces, which mean exactly the same thing as ionic bonds. There is no discrete molecular unit in an ionic compound. The word "molecule" does not apply.

Consequently, there is no such thing as an intermolecular force in an ionic compound. There are only ionic bonds.

I've heard that it's the ionic bond itself, but doesn't the bond remain after melting

Loosely speaking, it does not remain after melting. The reason why they have such high boiling points is therefore because of the fact that you have to break the ionic bonds for it to begin melting.

and even if it doesn't then how come covalent bonds don't cause the boiling and melting points in molecules?

Covalent bonds don't break during melting or boiling, with some exceptions (see: giant covalent compounds).

$\endgroup$
  • $\begingroup$ You say that in an ionic compound all the ions are held together by electrostatic forces. So in an NaCl lattice for example, every Na+ experiencse an Coulombic attraction towards every Cl- and this is the push against melting? What is the push against boiling then since the bonds don't remain in the liquid? Thanks a lot for all the time you've given me so far. $\endgroup$ – John Apr 24 '16 at 21:51
  • $\begingroup$ That's why I said loosely speaking. The Coulombic attraction remains in the liquid phase (it will always remain, even in the gas phase). You could think of it as: in the solid phase, the ions don't have enough energy so they remain stuck to each other. In the liquid phase, the ions have enough energy to "escape" each other momentarily, but they can't get sufficiently far away. In the gas phase, you've given them so much energy that they just fly everywhere, disregarding the attractions. Even this is kinda simplified though. en.wikipedia.org/wiki/Ionic_compound#Melting_and_boiling_points $\endgroup$ – orthocresol Apr 24 '16 at 21:56

Not the answer you're looking for? Browse other questions tagged or ask your own question.