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Melody Haratian 2J
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Postby Melody Haratian 2J » Thu Nov 19, 2020 1:57 pm

If there are many LDF interactions, can they become stronger than a dipole-dipole interaction?

Gabby Magat 3F
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Postby Gabby Magat 3F » Thu Nov 19, 2020 2:29 pm

From what I'm thinking, many LDF interactions could result from many atoms/molecules interacting with each other and those together can be very powerful. However, LDF occurs between molecules that experience instantaneous dipoles (like in nonpolar molecules for example) while dipole-dipole occurs within atoms/molecules that are in a permanent dipole moment (like an HF molecule, where F is much more electronegative, creating a dipole within the molecule).

I think this temporary-versus-permanent difference makes LDF a weaker interaction compared to dipole-dipole. But I can't exactly think of a molecule where "many" LDF's can combine to be stronger than a dipole-dipole interaction (maybe molecules as big as hydrocarbons that experience temporary dipole? I'm not too sure). I hope this is accurate, if not please correct me!

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Postby annabelchen2a » Fri Nov 20, 2020 10:20 am

My understanding is that london dispersion forces are temporary, so when comparing them to dipole-dipole interactions, they'll always be weaker no matter the amount. However, there may be specific molecular exceptions to that I don't know about, but I'm not sure what those instances may be.

Olivia Smith 2E
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Postby Olivia Smith 2E » Fri Nov 20, 2020 10:26 am

To add onto everyone point LDF will always be lower than dipole-dipole. But LDF is not the same for every molecule. Longer tubular like molecules will have greater LDF than spherical ones for example. So there may be variance in that regard, but these temporary changes in the atom will always heed to the more permanent state in dipoles

Sana Nagori 2H
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Postby Sana Nagori 2H » Fri Nov 20, 2020 10:19 pm

There's a bit in the textbook that talks about this regarding boiling points where it said that LDFs became more important than polarity but honestly it confused me.

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Postby MMorcus2E » Fri Nov 20, 2020 11:49 pm

LDFs are weak, temporary forces. So if there are other IMFs present, the other IMFS (like dipole-dipole) would play a bigger role in the attraction between atoms. However, if they are the only forces present, like in bonds between elements whose difference in electronegativity is very low, they would matter more, maybe even to the point of affecting boiling points and such.

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