Fluorocarbons

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Fluorocarbons

Post by Nevyn on Fri Jul 10, 2015 7:36 pm

Fluorocarbons are molecules containing only fluorine and carbon. There are some exceptions to the rule but we can ignore that for now. Most fluorocarbons are liquids although some form long chains or polymers. There are five fluorocarbons which are gases so we shall look at these first to see if they can tell us why only this group are gaseous.

The following image shows a Carbon atom and a Fluorine atom so that we can see what we are working with in these models.
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Tetrafluoromethane

Post by Nevyn on Fri Jul 10, 2015 7:38 pm

Tetrafluoromethane - CF4


The simplest fluorocarbon is Tetrafluoromethane with the formula CF4, also known as Carbon Tetrafluoride. A single carbon atom connecting to 4 fluorine atoms. This is one of the reasons carbon is thought to have 4 connection points but we find carbon is smarter than that for it can use only 2 to do the same job.



Each end of carbon allows up to 4 protons. Carbon contains 1 already but we only need 2 spots to add in a couple of fluorines. This allows 4 fluorines to bond with 1 carbon very easily. Notice how the outside of this molecule has the alpha-2 end of fluorine pointing out. This is what causes the molecule to form a gas. Although it is possible for 2 fluorines to bond at their alpha ends, it is not an easy bond to form and takes great pressure to force them together like this. Therefore CF4 can not normally form a liquid as it can not bond with itself.


Last edited by Nevyn on Fri Jul 10, 2015 9:39 pm; edited 1 time in total (Reason for editing : Subscripts do not work in the title)
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Hexafluoroethane

Post by Nevyn on Fri Jul 10, 2015 7:39 pm

Hexafluoroethane - C2F6


Hexafluoroethane, also known as Carbon Hexafluoride, has the formula C2F6 which means we are adding 1 carbon and 2 fluorines to CF4. These simply go inbetween the fluorine ends of CF4 like this.



This shows the general method of building Fluoroalkanes. We just insert a CF2 molecule into the chain which form very strong bonds. This is the way plastics are formed as these can build very long chains.


Last edited by Nevyn on Fri Jul 10, 2015 9:39 pm; edited 1 time in total (Reason for editing : Subscripts do not work in the title)
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Octafluoropropane

Post by Nevyn on Fri Jul 10, 2015 7:40 pm

Octafluoropropane - C3F8


Adding another CF2 into the chain gives us Octafluoropropane, also known as Carbon Octafluoride. See how the molecules are getting longer but they are not changing their general shape or charge patterns. They always present the alpha end of fluorine to the outside. The flat side, which we are looking at in these images, is very well protected and will act like a fuzzy wall of charge as all of the charge fields from the alpha-6's and 4's intermingle. This charge wall will keep away most unwanted entities from this area.



Last edited by Nevyn on Fri Jul 10, 2015 9:39 pm; edited 1 time in total (Reason for editing : Subscripts do not work in the title)
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Perfluoro-n-butane

Post by Nevyn on Fri Jul 10, 2015 7:42 pm

Perfluoro-n-butane - C4F10


Next we have Perfluoro-n-butane with the formula C4F10 and we now find that we have enough atoms to vary the structure since C4F10 can be used to build Perfluoro-iso-butane as well. Firstly though, we continue on our merry path and add another CF2 into Octafluoropropane.



This is the limit for gaseous fluorocarbons. If we add another CF2 to this structure we find it forms a liquid or solid.


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Perfluoro-iso-butane

Post by Nevyn on Fri Jul 10, 2015 7:43 pm

Perfluoro-iso-butane - (CF3)3CF


This is an alternative form using the same atoms as Perfluoro-n-butane.



Last edited by Nevyn on Fri Jul 10, 2015 9:40 pm; edited 1 time in total (Reason for editing : Subscripts do not work in the title)
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Boiling Points

Post by Nevyn on Fri Jul 10, 2015 7:46 pm

Boiling Points


We can now look at the boiling points of these molecules to see what it can tell us about them. The boiling point represents the amount of energy needed to seperate the molecules from each other. Another way to say that is the amount of charge each molecule needs to defend itself from other molecules of the same type.


FluorocarbonFormulaBoiling Point (°C)
TetrafluoromethaneCF4-128°
HexafluoroethaneC2F6-78.2°
OctafluoropropaneC3F8-36.5°
Perfluoro-n-butaneC4F10-2.2°
Perfluoro-iso-butane(CF3)3CF-1°
These gases show a clear relationship in their boiling points. As the number of atoms grows, so does the boiling point. This can be explained by the size of the molecules. CF4 is very small and doesn't need much energy to seperate the molecules from each other. None of these molecules bond with themselves but they can come quite close to each other as the ambient charge field drops and their protective charge walls lose strength. As the charge field rises in temperature, the charge walls start to come back to life. They will start to push on each other and seperate the molecules. It takes more energy to move a heavier molecule so the larger molecules require more heat before they have enough charge to operate correctly.

CF4 being so small allows it to become gaseous at only -128°C. It takes another 50° to boil C2F6 so even though we've only gained 1 carbon and 2 fluorines, it needs 50° more energy to seperate the molecules.

It is interesting to see the difference between perfluoro-n-butane and perfluoro-iso-butane. Sharing the formula C4H10 and only differing in configuration. Looking at them we can see that perfluoro-n-butane is much more compact which allows it to use the ambient charge field more effectively. Perfluoro-iso-butane contains a lot of space within its structure and this allows charge to leak away. The alphas adjacent to the empty space are not using all of their charge to repel other molecules so it takes a little bit more energy to boil perfluoro-iso-butane.
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Re: Fluorocarbons

Post by Nevyn on Sat Jul 11, 2015 7:42 pm

I have just noticed that these models use a different bonding scheme to my other Hydrocarbon models (which I ruled out in that discussion). This all came from some old research files I had so I may update them at some point such that each Fluorine atom joins to the Carbon atom in the same way that the Hydrogens connect to them in my Hydrocarbon models. This does not affect the boiling point analysis.
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