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Author Topic: Heavy Gases  (Read 18827 times)

Offline cuso4

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Heavy Gases
« on: 23/01/2004 11:06:05 »
Gases usually have small molecule mass, like H2, O2, CO2.
For a compound like SF6 which has a Mr of 108, you would expect it to be solid or liquid at room temperature but it's in fact a gas. How is this possible? Something to do with the interaction between molecles?

Angel

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Offline chris

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Re: Heavy Gases
« Reply #1 on: 23/01/2004 12:50:52 »
What is SF6 called ?! I had never hearrd of it.

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Offline nilmot

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Re: Heavy Gases
« Reply #2 on: 23/01/2004 13:39:22 »
Mmm...by the sound of the size of the molecule and it's Mr. The IMFs should be strong enough to keep it as a liquid. Could it have something to do with repulsion of the F molecules?

Tom
 

Offline Ylide

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Re: Heavy Gases
« Reply #3 on: 24/01/2004 01:10:12 »
Yes, that's exactly why, Tom.  The molecule is octohedral, with the fluorine atoms, which are on the edges of this octohedron, having the bulk of the electron density.  (due to their greater electronegativity)  This provides a repulsive force that is great enough to overcome any London forces that might hold the molecules together as a liquid.



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Offline nilmot

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Re: Heavy Gases
« Reply #4 on: 24/01/2004 09:38:54 »
Thank's cannabinoid, I was thinking about the high charge density F has and it's high electronegativity but couldn't quite come up with a conclusion.

Tom
 

Offline cuso4

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Re: Heavy Gases
« Reply #5 on: 26/01/2004 10:58:58 »
Thanks cannabinoid for the explanation.

Angel

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Offline chris

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Re: Heavy Gases
« Reply #6 on: 26/01/2004 12:27:43 »
So what is SF6 called ?

Sulphur hexafluoride ?

Chris

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Offline Ylide

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Re: Heavy Gases
« Reply #7 on: 26/01/2004 16:27:11 »
Yep, that's what it's called. (except we spell it "sulfur")  =P  



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Offline cuso4

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Re: Heavy Gases
« Reply #8 on: 27/01/2004 11:09:15 »
Are there any other examples of heavy gases?

Angel

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Offline chris

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Re: Heavy Gases
« Reply #9 on: 27/01/2004 22:59:06 »
quote:
except we spell it "sulfur"



Well it needs to be made simple for americans ;)

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Offline Donnah

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Re: Heavy Gases
« Reply #10 on: 27/01/2004 23:46:53 »
Jay says tomato, Chris says tomatoe, Jay says potato, Chris says potatoe...let's call the whole thing off.  Anybody else old enough to remember that song?
« Last Edit: 27/01/2004 23:51:33 by Donnah »
 

Offline Ylide

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Re: Heavy Gases
« Reply #11 on: 28/01/2004 01:44:53 »
Yes, and thanks Donnah, that song's stuck in my head now.  :P

Chris, I don't see it as "simple", but rather I see it as efficient.  Now the Germans...those folks have some BIG words.

Angel, Just about any semi-spherical polyfluoridated molecule will be a gas for reasons we discussed above. (uranium hexafluoride for instance)  Some elemental gases are still pretty heavy too, like radon (molar mass 86), elemental iodine (I2 crystals will sublime at room temperature, molar mass is somewhere around 106)  Even carbon dioxide, at a lowly mass of 44 is considered to be heavy, as Argon and Xenon.

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Offline tweener

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Re: Heavy Gases
« Reply #12 on: 28/01/2004 04:29:56 »
Jay walked right into that and deserved what Chris dished out!  And, yes, I'm old enough to remember that song.  I never remember all the words to a song, but I can hear the whole orchestra playing the tune.


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John
 

Offline Supercryptid

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Re: Heavy Gases
« Reply #13 on: 01/02/2004 05:20:22 »
Radon is even heavier than sulfur hexafluoride, having a mass number of 222. I suspect that this element is a gas because it is has a spherical atom. A sphere provides the least surface area for a given amount of volume. This gives the electrons less of an oppotunity to be far away from each other, so the london dispersion forces are at a mininum.

Interestingly enough, I think I once calculated that radon is so dense that a piece of aerogel (the least dense known solid) would actually rise and float in it. This is the only circumstance I can think of where a gas is more dense than a solid.
 

Offline Ylide

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Re: Heavy Gases
« Reply #14 on: 01/02/2004 08:40:41 »
I read recently that aerogels are only twice as dense as air.  That would mean that in a given volume of aerogel, the mass of the actual solid matter atoms is equal to the mass of the air in the empty space between them.  

Anyway density is a function of mass and volume, which for gases is a function of the temperature, pressure, and amount of gas present.  I could make hydrogen more dense than aerogel given a rigid container and enough moles of hydrogen.  ;)

Unless of course you're referring to standard temp


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Offline chris

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Re: Heavy Gases
« Reply #15 on: 02/02/2004 00:28:10 »
This is a great thread, I'm learning a huge amount from it. But can someone please clarify what London forces are when they're at home ?

Cheers,

Chris

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Offline Supercryptid

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Re: Heavy Gases
« Reply #16 on: 02/02/2004 04:28:30 »
London dispersion forces are the forces of attraction between molecules that is due to temporary dipole movements of the electrons in the molecules. In any given molecule, electrons are moving around inside of the molecule. Sometimes the electrons are on one side of the molecule. At other times, they are on the opposite side of the molecule. This causes the molecule to become temporarily charged on opposite sides, like a tiny magnet.

This magnet-like state in the molecules causes the molecules to be weakly attracted to one another. These are called dispersion forces. This is what keeps all molecules held together in a substance. Some other substances have other forces holding them together as well, such as permanent polar dipole moments and hydrogen bonds.
 

Offline Ylide

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Re: Heavy Gases
« Reply #17 on: 02/02/2004 14:38:29 »
Great explanation.



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Offline nilmot

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Re: Heavy Gases
« Reply #18 on: 03/02/2004 09:00:47 »
So a bit like Van der Waals' forces, (temporary dipole-induced dipole forces)

Tom
 

Offline Ylide

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Re: Heavy Gases
« Reply #19 on: 03/02/2004 15:47:48 »
Same thing, different name.



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Offline parvo

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Re: Heavy Gases
« Reply #20 on: 05/02/2004 07:33:36 »
I was wondering are there any gases that are heavier than water? If so, would releasing the gas/es in water cause the formation of a bubble that sinks rather than rises?

Tah, Ben
 

Offline nilmot

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Re: Heavy Gases
« Reply #21 on: 05/02/2004 12:11:14 »
I don't think there are any natural ones, it will have to be artificial. It's quite possible but to find and collect a significant amount; then insert them into water might be quite costly.

Tom
 

Offline Ylide

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Re: Heavy Gases
« Reply #22 on: 05/02/2004 19:36:50 »
Heavier is not the same as more dense.  You won't see any gases sink in water because of the space between molecules of the gas creating a lower density.

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Re: Heavy Gases
« Reply #22 on: 05/02/2004 19:36:50 »

 

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