DAT Destroyer Question 2015 GC #31

[biofilmDentist007]

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I was looking at this question and thought that ionic bonds are not intermolecular forces, I knew that molecular solids have high melting points, but according to Chad ionic bonds are not intermolecular forces, if anyone could clear that up for me that be great. Thanks

 

[Cool Beans]

I don't have a copy of Destroyer in front of me but I'll add my 2 cents.

First of all molecular solids don't generally have high melting points. Network covalent solids (like diamond and quartz) have high melting points but molecular solids generally have much lower melting points than either network covalent solids or ionic compounds.

As far as ionic compounds go, they are held together by a very strong force (ionic bonds) but it would be a mistake to call it an 'intermolecular' force as ionic compounds don't exist as molecules...only molecular compounds exist as molecules (hence the name) and have intermolecular forces. However you will have to take this into consideration when evaluating melting points. Generally network covalent solids and ionic compounds will have the highest melting points as they are held together by covalent and ionic bonds respectively. After these you would then have to compare molecular compounds which are only held together by the relatively weaker intermolecular forces and your comparison of molecular compounds would be based upon what you know about their intermolecular forces (H-bonding, dipole-dipole, London dispersion).

Hope this helps to clarify!

 

[738177]

Sorry to bump and old thread but i was looking for confirmation on this question as well. I narrowed it down to B and D and picked D solely because i thought Ionic Bonds are Intramolecular as opposed to Intermolecular. Was this a mistake on Destroyer or did i miss something? Destroyer says the correct answer is B.
For reference, the question was: Which statement is False? I narrowed it down to
B. Molecular solids have high melting points
D. Concerning intermolecular forces, the trend from weakest to strongest is London Dispersion < Dipole - Dipole < Hydrogen bonding < Ionic

 

[aj30]

Sorry to bump and old thread but i was looking for confirmation on this question as well. I narrowed it down to B and D and picked D solely because i thought Ionic Bonds are Intramolecular as opposed to Intermolecular. Was this a mistake on Destroyer or did i miss something? Destroyer says the correct answer is B.
For reference, the question was: Which statement is False? I narrowed it down to
B. Molecular solids have high melting points
D. Concerning intermolecular forces, the trend from weakest to strongest is London Dispersion < Dipole - Dipole < Hydrogen bonding < Ionic

Yes, you technically are right. I was even in class with Dr. Romano and he confirmed that the question is valid and the language is somewhat imprecise but "don't think too much into it" (he's not trying to get so nit picky).

I would add my 2 cents though, that ionic bonds sometimes CAN be intermolecular. Consider NH4Cl, ammonium chloride. Try drawing a Lewis structure and you'll see you can't connect the NH4+ and Cl- using traditional Lewis bond lines, and so in real life you can't really say that the 2 are "sharing a bond" and are one single compound. Rather, it would be more accurate to think of 2 separate ions that are just attracted to each other based on opposite charges.
This stands in contrast with most ionic bonds, like in NaCl. here, they "share a bond" in the sense that a pair of electrons are taken away from Na to Cl, and now there's a bond between them. Draw this Lewis structure and you'll see that.

Point being that although ionic is generally intra, it can be inter as well. If you find the above confusing though, just leave it as is, that you're right about your question.