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Topic: low polarizability of fluorine???  (Read 12379 times)

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Offline Agent-X

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low polarizability of fluorine???
« on: July 09, 2009, 09:33:39 PM »
 ???

What does it mean when fluorine has a low polarizability?

I guess it relates to these compounds:
CH3CH2F CH3CHF2 CH3CF3 CF3CF3

I don't understand it, though.

For what I remember, when a compound is polarized, such as HCl, that means that the chlorine is pulling electrons toward it. Am I to infer that fluorine is not pulling electrons toward it as much as Cl would? Why would I infer that?

I don't understand it. Maybe it relates to inorganic chemistry. It's been a while.

Quote
The boiling point of CF3CF3 is, in fact, only 11° higher than that of ethane itself. The reason for this behavior has to do with the very low polarizability of fluorine and a decrease in induced-dipole/induced-dipole forces that accompanies the incorporation of fluorine substituents into a molecule.
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Offline StarvinMarvin

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Re: low polarizability of fluorine???
« Reply #1 on: July 10, 2009, 05:41:26 PM »
In my view, the reason behind the "low polarizability" lies within the compact structure of fluorine. While it is the most electronegative element, fluorine has a very small atomic radius which makes its lone pairs not very eager to incorporate into hydrogen bonds or other interactions. And that would be the reason for such a small difference in bp of fluorinated hydrocarbons.

Offline zxt

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Re: low polarizability of fluorine???
« Reply #2 on: July 11, 2009, 03:01:25 AM »
Fluorine is the most electronegative element and it should has a strong polarizability due to its very short atom radius with a strong positive nuclear. And its most outside orbit has a number of electrons of 7 which's structure is 2s22p5.So, it' very easy to attract another one electron to fullfill its P orbit reaching the steady status of 8 electrons in the most outside orbit like inert gas.Because of its strong electronegativity, Fluorinated Hydrogen compounds can form strong Hydrogen bond to make those compounds of high bp and mp.

Offline StarvinMarvin

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Re: low polarizability of fluorine???
« Reply #3 on: July 11, 2009, 06:42:32 AM »
This was only my personal thinking outloud. Then again, how to explain this phenomenon of only 11 degrees difference between thoser two hydrocarbons? Because, it clearly would contradict with theory.

Offline zxt

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Re: low polarizability of fluorine???
« Reply #4 on: July 12, 2009, 05:48:02 AM »
This was only my personal thinking outloud. Then again, how to explain this phenomenon of only 11 degrees difference between thoser two hydrocarbons? Because, it clearly would contradict with theory.

Because there is no H element in CF3CF3,so it cannot form Hydrogen bond.That's why only 11deg C
difference. As to CF3CF3,  the two end of the molecule is negative while the middle of it is positive, so molecules repel each other at the heads of molecule(which causes it hard to form deduced dipole/ deduced dipole attraction along this direction but not due to Fluorine's low polarizability,actually caused by Fluorine 's strong polarizability) meanwhile attract each other at the center part. And CF3CF3's molar mass is heavy than that of ethane.Considering all factors above, the difference in bp will not be high.
« Last Edit: July 12, 2009, 05:59:23 AM by zxt »

Offline nj_bartel

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Re: low polarizability of fluorine???
« Reply #5 on: July 12, 2009, 06:08:41 AM »
Polarizability and ability to create an inductive EW effect aren't the same thing, are they?

Small shell with high electronegativity means fluorine atoms hold their electrons in place close to the nucleus.  Fluorine's electrons are not very polarizable, at all.

Offline zxt

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Re: low polarizability of fluorine???
« Reply #6 on: July 12, 2009, 06:17:17 AM »
Polarizability and ability to create an inductive EW effect aren't the same thing, are they?

Small shell with high electronegativity means fluorine atoms hold their electrons in place close to the nucleus.  Fluorine's electrons are not very polarizable, at all.

Oh yes, I know what you mean. I misunderstood the word "polarizability". What I mean is other elements are easily polarizable by the effect of Fluorine but Fluorine itself is hard to polarize.Thx a lot and I'm from China majoring in Chemical Engineering.

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