London Dispersion Forces

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Jessica Manriquez 1H
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London Dispersion Forces

Postby Jessica Manriquez 1H » Sat Nov 14, 2020 12:50 am

Hi all! Im kind of confused on the interpretation of London forces, and was wondering if anyone has good way to distinguish these from other types of bonds. Thank you in advance :)

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Re: London Dispersion Forces

Postby BrittneyMyint1D » Sat Nov 14, 2020 1:17 am

Hello! Some main things you should know about London dispersion forces is that it is a temporary intermolecular force that occurs in all molecules. So, while the other forces tend to have molecules that are polar, like in dipole-dipole, London dispersion forces can occur even between nonpolar molecules. London forces occur due to some fluctuating electron density. One example that Lavelle used was with N2. From my understanding, there could be a time when one N in a N2 molecule is partially positive, so it influences the other N2 molecule and makes one of its N partially negative, which makes an induced dipole-induced dipole interaction between the molecules, or London dispersion force. Hope this makes sense!

Selena Quispe 2I
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Re: London Dispersion Forces

Postby Selena Quispe 2I » Sat Nov 14, 2020 1:20 am

Hi! London Dispersion forces are the weakest intermolecular force. LDF is pretty much anything that interacts with each other. So hydrogen bonding has LDF, Dipole-Dipole has LDF. However, London dispersion forces are mainly in non-polar molecules. So for example, all hydrocarbons are only LDF because they are non-polar (there is an equal pull). I hope this helps!!

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Re: London Dispersion Forces

Postby Nan_Guan_1L » Sat Nov 14, 2020 6:20 am

Hi! just to add on to the discussion above. I think what separates LDF from other intermolecular forces is that it exists in all kinds of molecules, no matter what other intermolecular bonds are there. while they are the weakest, some molecules are held together only/mainly by LDF, such as the halogen family, or CO2, methane and other non polar molecules. Other polar molecules also have LDF as a contributing force that holds the molecules together, but compared with say covalent bonds / ionic bonds, LDF is much weaker. Hope that helps!

Vince Li 2A
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Re: London Dispersion Forces

Postby Vince Li 2A » Sat Nov 14, 2020 8:06 pm

This is what my high school teacher explained, and I use it to grasp the concept even further. It is not very scientific, but it helps me. Think of a nonpolar molecule. Obviously, there is no natural dipole (one side having slightly positive charge and another side having negative charge) in a nonpolar molecule such as CH4. However, imagine that all of the electrons are moving, and at some point in time, one particular moment in time, all of those electrons are in a position that causes a dipole. You can almost think of it like a probability. When those electrons are in that specific position, the repulsion of the electrons generates a dipole.

Ethan Goode 2H
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Re: London Dispersion Forces

Postby Ethan Goode 2H » Sat Nov 14, 2020 8:36 pm

London Dispersion Forces occur in all molecules. Basically, they are just super weak, temporary bonds, which revolve around the idea that electron clouds have different charges at different parts of the electron cloud, allowing for a weak bond between any molecule.

Chinyere Okeke 2J
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Re: London Dispersion Forces

Postby Chinyere Okeke 2J » Sat Nov 14, 2020 9:04 pm

London Dispersion Forces (LDF) are intermolecular forces that occur between ALL molecules when they interact. Be it ions with ions, dipole-dipole, nonpolar-nonpolar, polar-polar interactions. This is because LDF occurs when electron clouds temporarily fluctuate as they get close and gain temporary charges. However, it is good to remember that these charges aren't fixed and can change.

In addition, LDF bonds are the weakest of the bonds that we learned about.

David Y
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Re: London Dispersion Forces

Postby David Y » Sun Nov 15, 2020 3:16 pm

All molecules have them, but the bigger the atom's size, the stronger the force

David Facio 1K
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Re: London Dispersion Forces

Postby David Facio 1K » Sun Nov 15, 2020 3:48 pm

If you've ever taken or plan on taking the LS7 series, you know or will learn that London (aka Van der Waals Forces) are present in every type of molecule.

London dispersion forces occur because of partially negatively charged regions and partially positively charged regions.

Take the interaction of two Methane, CH4, molecules as an example.

The closer the two methane molecules get, the more their electron cloud's charges fluctuate.
The TEMPORARY opposite partial charges cause an attraction.

Because the electrons of the methane molecule are continuously interacting with one another,
the electrons will accumulate more to one region for a short period of time,
making that region of the molecule negatively partially charged,
and the other region with less electrons partially positively charged.

These opposing partial charges are NOT TO BE CONFUSED WITH:
A) ionic bonding
B) polar covalent bonds or
C) hydrogen bonding

Because the methane molecule is neither a salt formed by a cation/anion bond (A),

It is not a molecule with consistently unbalanced charges such as H20 (B),

and it is not an electrostatic bond between Hydrogen and any of the following elements (N, O or F) with an available lone pair (C).

hope this helps :)

Marco Vivar 3G
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Re: London Dispersion Forces

Postby Marco Vivar 3G » Mon Nov 16, 2020 12:48 am

LDF occurs in all molecules however it is the weakest of the bonds

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Re: London Dispersion Forces

Postby apurva-3E » Mon Nov 16, 2020 2:25 am

They are induced dipole induced dipole interactions. Basically as the electron density fluctuates, molecules form temporary dipoles with each other.

Annette Fishman
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Re: London Dispersion Forces

Postby Annette Fishman » Mon Nov 16, 2020 9:02 am

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two atoms occupy positions that make the atoms form temporary dipoles.

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