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Thread: Van der Waals forces...

  1. #1 Van der Waals forces... 
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    i had read about Van der Waals forces in my textbook, and on wikipedia too, but still, i dun understand what are they....

    can someone please explain what are Van der Waals forces? and why that like in Group 18 of the periodic table, the noble gases, the bigger the size of the atoms, the greater the Van der Waals forces?? thx ....


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  3. #2  
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    From what I know, it is how the larger noble gases become liquids. The larger the atom, it becomes more like a dipole, the electron cloud not forming a perfect sphere, and thus it can be condensed into a liquid. I hope that answers your question (and I hope I'm accurate on this).


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  4. #3 Re: Van der Waals forces... 
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    Quote Originally Posted by randytsx
    i had read about Van der Waals forces in my textbook, and on wikipedia too, but still, i dun understand what are they....

    can someone please explain what are Van der Waals forces? and why that like in Group 18 of the periodic table, the noble gases, the bigger the size of the atoms, the greater the Van der Waals forces?? thx ....
    Van der Waals forces are the forces between molecules. I am not sure of the rest.
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  5. #4 hmm 
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    but...those noble gases are monoatomic, so that means...they are atoms, right?
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    well, i read abt this somewhere, but can't remember!!! i think they are about the forces between molecules, as SinMan said.....
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    In symetrical molecule such as CH4, you would expect eletrons to be equally shared between the four hydrogen atoms as they have equal electronegativity values. This is true to an extent which is why these types of molecules are called non polar as generally no hydrogen will have more electrons than another. However in actual fact you will get random fluctuations within the orbitals called temporary dipoles, so at one moment there might be more electrons on one side of the molecule giving that side a slight negative charge, and on the other side less giving a slight positive charge.

    These temporary dipoles will disrupt neighbouring atoms orbitals giving them an induced dipole also making them slightly polar. As opposites attract, the slightly negative side or hydrogens on one molecule will be attracted to the slightly positive hydrogens on another, giving rise to a weak intermolecular bond. As atoms and molecules get bigger, there are more electrons and greater charges involved so inevatably the bonding will be stronger. This is the reason why smaller hydrocarbons such as methane exists as a gas and why larger molecules such as octane exist as liquids.

    Anyway hope that kinda made sense. You might wanna check out this actually http://www.chemguide.co.uk/atoms/bonding/vdw.html#top it probably explains it better than i did.
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  8. #7 Re: hmm 
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    Quote Originally Posted by randytsx
    but...those noble gases are monoatomic, so that means...they are atoms, right?
    yo, randy

    well, noble gases ( Helium, Neon, Argon, Krypton, Xenon, Radon and Ununoctium ) are diatomic (2 atoms) molecules as far as I know. I just dont have time to search references.
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  9. #8  
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    Noble gases come in single atoms. Their outer shell is filled (two electrons in the case of helium, eight in all other instances). This is is what gives them their disinclination to form compounds.
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  10. #9  
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    Lucky explained it pretty well.
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  11. #10  
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    Quote Originally Posted by Ophiolite
    Noble gases come in single atoms. Their outer shell is filled (two electrons in the case of helium, eight in all other instances). This is is what gives them their disinclination to form compounds.

    Hi ophiolite, I think it's not entirely correct what you state. Gases are not the same as atoms. In fact so 'noble gases' don't come in single atoms. This was just a correction. Thank you.
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  12. #11  
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    As Ophiolite said noble gases have full valence shells which means they have electronegativity values of 0. Becasue of this intermolecular forces cannot exist between each atom so they are always with out exception monoatomic.
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  13. #12  
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    i guess I was wrong. apologize
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