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Topic: Non-covalent interactions  (Read 309 times)

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Offline liravsc

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Non-covalent interactions
« on: November 16, 2021, 02:09:34 PM »
I'm studying for an exam, the question is simple but I'm taking a class that's not part of my course, so my chemistry is rusty.

What kind of non-covalent interactions keep the following solids together:

a) NaCl

b) Graphite
« Last Edit: November 16, 2021, 02:47:49 PM by liravsc »
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Offline Orcio_Dojek

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Offline liravsc

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Re: Non-covalent interactions
« Reply #2 on: November 16, 2021, 02:52:18 PM »
That answers about graphite but not NaCl.

But really this isn't a "homework" question. What gives that graphite is a van der waals interaction?

Thanks
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Offline Babcock_Hall

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Re: Non-covalent interactions
« Reply #3 on: November 16, 2021, 03:18:21 PM »
It is a forum rule that you must show your attempt or provide your thoughts before we can help you.

Offline liravsc

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Re: Non-covalent interactions
« Reply #4 on: November 16, 2021, 04:10:50 PM »
I thought Graphite was van der waals through exclusion, but I'm not sure what shows me in the molecule that it is, what gives it away. And I thought NaCl was electrostatic interaction, just because Na+ Cl-. I'm arriving almost a month late to this class, it took a while for my deem to approve it, it's extracurricular, so I don't want to bother the Professor with late subjects. Thank you!
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Offline Babcock_Hall

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Re: Non-covalent interactions
« Reply #5 on: November 16, 2021, 04:33:41 PM »
The ions in sodium chloride are indeed attracted via electrostatics.  London forces are one type of Van der Waals attraction, and they arise from instantaneous (not permanent) dipoles.
EDT
One article I skimmed argued that metallic forces were more important, but I don't know if this is the consensus view.
http://przyrbwn.icm.edu.pl/APP/PDF/112/a112z308.pdf
« Last Edit: November 16, 2021, 05:00:50 PM by Babcock_Hall »

Offline liravsc

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Re: Non-covalent interactions
« Reply #6 on: November 16, 2021, 05:03:05 PM »
The ions in sodium chloride are indeed attracted via electrostatics.  London forces are one type of Van der Waals attraction, and they arise from instantaneous (not permanent) dipoles.

Thank you! We havent been through the kinds of Van der Waals yet. I'll just rule it out by exclusion then. The class is "celular biochemistry I". Bye. ;D
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Offline Corribus

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Re: Non-covalent interactions
« Reply #7 on: November 16, 2021, 05:55:03 PM »
There seems to be a lot of confusion about this, but every intermolecular interaction is usually regarded as an electrostatic interaction. Electrostatic forces are just forces between charges that are at rest on the timescale over which the force is applied. All molecules are held together by forces between charges. Actually excluding forces that hold nuclei together, all matter is held together by forces between charges. Chemistry is basically the study of electrostatic interactions. We can classify these electrostatic, intermolecular interactions in a lot of different ways, but most of them come down to whether the interacting electric charges are permanent (usually stronger) or transient (usually weaker). Graphene is a little weird because it has some metallic properties, which might be described somewhat as interactions between nearby stacking pi electron systems. It would be safe to lump these under the broad category of van der Waals forces, which 
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline liravsc

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Re: Non-covalent interactions
« Reply #8 on: November 16, 2021, 06:22:00 PM »
There seems to be a lot of confusion about this, but every intermolecular interaction is usually regarded as an electrostatic interaction. Electrostatic forces are just forces between charges that are at rest on the timescale over which the force is applied. All molecules are held together by forces between charges. Actually excluding forces that hold nuclei together, all matter is held together by forces between charges. Chemistry is basically the study of electrostatic interactions. We can classify these electrostatic, intermolecular interactions in a lot of different ways, but most of them come down to whether the interacting electric charges are permanent (usually stronger) or transient (usually weaker). Graphene is a little weird because it has some metallic properties, which might be described somewhat as interactions between nearby stacking pi electron systems. It would be safe to lump these under the broad category of van der Waals forces, which

Thanks for the intel. We are using the book Biochemistry by Jeremy M. Berg, John L. Tymoczko, and Lubert Stryer; which puts "electrostatic interactions" under "non covalent interactions", together with Van der Waals and hydrogen bridges.
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Offline Babcock_Hall

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Re: Non-covalent interactions
« Reply #9 on: November 17, 2021, 10:35:12 AM »
Subdividing and classifying the various intermolecular forces as Berg and coauthors did is standard for biochemistry and introductory organic chemistry textbooks.  There is some sense in treating instantaneous dipoles and permanent dipoles separately, for example.  Hydrogen "bridges" are usually called hydrogen bonds.  In this way of looking at things, electrostatic interactions happen between two ions, whereas ion-dipole forces are what attracts an ion to water, for example.

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