emerge123
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#1
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#1
please could someone explain to me what van der waals are and what they do? thank you
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NNB_Herath
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#2
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(Original post by emerge123)
please could someone explain to me what van der waals are and what they do? thank you
Van der waal forces have several names such as London forces.
They are the weakest kind of intermolecular forces that exist between molecules !!

Hope you understood !!
Reply or message me for more detail !
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username1539513
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#3
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(Original post by emerge123)
please could someone explain to me what van der waals are and what they do? thank you
They are a intermolecular force based on temporary dipoles inbetween molecules. They happen due to the movement of electrons within molecules. They are the weakest intermolecular force but increase with strength with proportion to the number of atoms in a molecule
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emerge123
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#4
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(Original post by NNB_Herath)
Van der waal forces have several names such as London forces.
They are the weakest kind of intermolecular forces that exist between molecules !!

Hope you understood !!
Reply or message me for more detail !
okay so please could you explain to me what temporary dipoles are and what are induced dipoles and howdo you know that they are there
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NNB_Herath
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#5
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It is NOT only valid for solutions....i guess you should edit your post
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username1539513
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#6
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(Original post by NNB_Herath)
It is NOT only valid for solutions....i guess you should edit your post
Tah, been a while since I've done chemistry
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CheeseIsVeg
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#7
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(Original post by emerge123)
please could someone explain to me what van der waals are and what they do? thank you
Van der waals are intermolecular forces of attraction between covalent compounds due to an imbalance in electrons in the compound which induces a temporary dipole on the molecule which attracts/repels a neighbouring molecule (therefore inducing s dipole on it)

This arises due to the random arrangement of the shared pair of electrons within a convalent bond.
For one instance, in a I-I covalent bond, the electron pair xoild be closer to the 2nd I atom. This would make it slightly more negatively charged and induce a delta - and delta + temporary dipole.
Then say this is put next to another I-I, it would repel one side and attract another due to the slightly -ve dipole
This force of attraction is hereby named van der waal forces
It is good to note that they are very weak

Sorry for typos, on phone
Hope this helps, feel free to ask questions
Cheese
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NNB_Herath
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#8
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(Original post by emerge123)
okay so please could you explain to me what temporary dipoles are and what are induced dipoles and howdo you know that they are there
I guess this will explain you
https://www.youtube.com/watch?v=3t1Jn_jrsQk
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emerge123
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#9
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(Original post by NNB_Herath)
I guess this will explain you
https://www.youtube.com/watch?v=3t1Jn_jrsQk
that did not help please could you explain dipoles in details
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Reality Check
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#10
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(Original post by emerge123)
that did not help please could you explain dipoles in details
Permanent dipole-dipole interactions, or induced? You've broadened out your question somewhat from the original.
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NNB_Herath
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#11
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#11
(Original post by emerge123)
that did not help please could you explain dipoles in details
This will help you then
https://www.youtube.com/watch?v=08kGgrqaZXA
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emerge123
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#12
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(Original post by Reality Check)
Permanent dipole-dipole interactions, or induced? You've broadened out your question somewhat from the original.
can someone please explain as to what permenant dipoles are and what are induced dipoles I am unable to understand what they are after going through it many times.
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username1539513
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#13
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#13
(Original post by emerge123)
that did not help please could you explain dipoles in details
What about dipoles don't you understand?

Temporary dipoles are due to the continuous movement of electrons within sub-shells of atoms which create temporary positive and negative areas between molecules thus resulting in attraction. These are your VDW/ London forces and happen between any molecules.

Permanent dipoles are different as they come about due to the difference in electronegativity between two atoms on a covalent bond and between molecules that have differing significant electronegativity. For example, there would be dipole-dipole attraction between molecules of HCl. They are stronger than VDW forces but weaker than hydrogen bonds.
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emerge123
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#14
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#14
so okay this has helped but please could you now explain to me as how you know which element in a compound is more electro negative and also of the topic how does shielding effect how hard or easy it is to remove an electron - I need to ask about shielding because I am unable to understand the concept of how and what repulsion is as that is what is said what happens in shielding
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Reality Check
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#15
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Permanent dipoles occur when two atoms with different electronegativities make a 'covalent' bond, such a hydrogen and bromine atom forming the molecule HBr. The bromine atom is more electronegative, i.e. it is 'hungrier' for electrons and pulls the electron cloud away from the hydrogen atom.This results in the molecule becoming polar, with the hydrogen gaining a slight positive charge ∂+, and the bromine ion gaining a slight negative charge, ∂-. These now polar molecules can then go on to form weak interactions with other polar molecules with similarly imbalanced charge distribution. Note that the bond in HBr, like the other halogen halides, actually shares characteristics of both covalent and ionic- bonding.

Induced dipoles are when the charge cloud of one atom temporarily disrupts the charge cloud of another molecule if it gets close enough - again, it leads to slightly positive and slightly negative charges on both atoms, which are then attracted to each other. The strength of these interactions depends of things like temperature, charge of the atom, radius, etc. but these Van de Waals forces are weak singularly but add up in quantity!

Does this help you?
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emerge123
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#16
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#16
(Original post by Reality Check)
Permanent dipoles occur when two atoms with different electronegativities make a 'covalent' bond, such a hydrogen and bromine atom forming the molecule HBr. The bromine atom is more electronegative, i.e. it is 'hungrier' for electrons and pulls the electron cloud away from the hydrogen atom.This results in the molecule becoming polar, with the hydrogen having a slight positive charge ∂+, and the bromine ion have a slight negative charge, ∂-. These slightly polar molecules can then go on to form weak interactions with other molecules with similarly imbalanced charge distribution. Note that the bond in HBr, like the other halogen halides, actually shares characteristics of both covalent and ionic- bonding.

Does this help you?
how can you determine when an element is polar and non- polar in a compound
thank you
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Reality Check
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#17
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#17
(Original post by emerge123)
how can you determine when an element is polar and non- polar in a compound
thank you
See my edit for a more complete answer to your question.

Yes, you can - if there is a difference in electronegativity between the bonded atoms, then the chances are that the bond produced will be polar.

So in Hydrogen fluoride, HF, fluorine is the most electronegative atom (4) and strongly draws the electron density cloud towards it - HF is strongly polar. Going down the period, as you know the electronegativities decrease, so hydrogen iodide, HI is still polar, but not nearly as much as HF.

A perfectly non-polar bond exists in diatomic molecules, such as Cl2, because the same molecules obviously have the same electronegativity! However, induced dipoles can occur in these molecules in the same way as I've sketched above.

Do both of these posts of mine explain it to you?
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username1539513
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#18
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#18
(Original post by emerge123)
so okay this has helped but please could you now explain to me as how you know which element in a compound is more electro negative and also of the topic how does shielding effect how hard or easy it is to remove an electron - I need to ask about shielding because I am unable to understand the concept of how and what repulsion is as that is what is said what happens in shielding
Okay, usually if there's a question on it they'll tell you the electronegativity values in a question but as a general rule oxygen, fluorine, chlorine and nitrogen are all more electronegative than carbon, (hence hydrogen bonds exist)

Electron shielding as a similar topic but off the scope of this thread. I might get carded for derailing here so VM me instead?
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Mystery.
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#19
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#19
They are the umbrella term for intermolecular bondingd which exists between atoms in a molecule.
Examples of van der waals include London dispersion forces, permanent dipole attractions, hydrogen bonding.
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DarkEnergy
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#20
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#20
(Original post by Mystery.)
They are the umbrella term for intermolecular bondingd which exists between atoms in a molecule.
Examples of van der waals include London dispersion forces, permanent dipole attractions, hydrogen bonding.
Is it an umbrella term? I've always thought vdW forces were just a type of intermolecular forces, synonymous with temporarily induced dipole-dipole forces.
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