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Offline AdiDex

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Evidence of ions
« on: November 06, 2015, 04:02:58 AM »
I was reading Inorganic chemistry : Principles of structure and reactivity (By James E. Huheey ) . I found this paragraph in it.

We have no absolute proof of the existence of ions in solid Sodium Chloride . For example thogh our best example that ions are found when it is melted or dissolved in water does not prove that they existed in the solid crystal.

My question is that " what is the present scenario of this problem ?? " . Have we found something new ???

Offline Hunter2

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Re: Evidence of ions
« Reply #1 on: November 06, 2015, 04:35:27 AM »
No I don't think so. What he is saying means we get ions if we melt or dissolve a salt. That does not automatically mean the Crystal contains already the ions. They can be produced during melting or dissolving. But if this is not the case has to be proven with other methods on the crystal salt.

Online Arkcon

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Re: Evidence of ions
« Reply #2 on: November 06, 2015, 07:13:36 AM »
What are some of the methods used to study solids? What evidence do they give us to support or deny ions ina crystalline solid?  These sorts of questions can help you understand what you're really asking.  Although the absolute reality can become metaphysical rapidly.
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Offline kriggy

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Re: Evidence of ions
« Reply #3 on: November 06, 2015, 08:47:17 AM »
Cant you distinguish between ions and covalently bonded atoms by Xray difraction?

Offline AdiDex

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Re: Evidence of ions
« Reply #4 on: November 06, 2015, 10:18:58 AM »
No I don't think so. What he is saying means we get ions if we melt or dissolve a salt. That does not automatically mean the Crystal contains already the ions. They can be produced during melting or dissolving. But if this is not the case has to be proven with other methods on the crystal salt.
yep I agree. By the way i was asking the same .

Offline AdiDex

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Re: Evidence of ions
« Reply #5 on: November 06, 2015, 10:27:16 AM »
Cant you distinguish between ions and covalently bonded atoms by Xray difraction?
As fas as I know X-Ray Diffraction is used to determine the interatomic distance . Can you please elaborate your view ?? I have not read X-ray diffraction in so much detail .

Offline kriggy

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Re: Evidence of ions
« Reply #6 on: November 06, 2015, 11:19:33 AM »
Yes it is used to determine interatomic distances, position of atoms and can determine types of atoms too. I would guess that if there is electron missing from the atom it would provide different difraction patter and thus it could be identified by xray. I have, sadly, only very basic knowledge of this technique so my post was more question whether it is possible rather than suggestion of technique

Offline Borek

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Re: Evidence of ions
« Reply #7 on: November 06, 2015, 12:52:15 PM »
Some of the methods used in crystallography allow measuring of the electron density inside the crystal (they create a density map). That's as close as you can get to finding ions in solid.
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Offline AdiDex

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Re: Evidence of ions
« Reply #8 on: November 08, 2015, 12:06:22 AM »
Some of the methods used in crystallography allow measuring of the electron density inside the crystal (they create a density map). That's as close as you can get to finding ions in solid.

Can you tell me the name of That method ?? do you know when it was invented ??

Now I am wondering why James E. Huheey think that there is no absolute proof ?? As I have one more book which is quite old (1970's book ) , It also have X-Rays  and Electron Density .

Offline Irlanur

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Re: Evidence of ions
« Reply #9 on: November 08, 2015, 04:18:37 AM »
I mean you can also generalize and ask "are there atoms in molecules" ?

Offline AdiDex

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Re: Evidence of ions
« Reply #10 on: November 08, 2015, 04:29:18 AM »
I mean you can also generalize and ask "are there atoms in molecules" ?

I think there should be atoms , How can you define molecule without atom ?? I think here is the question about their bonding ...!!

Offline Borek

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Re: Evidence of ions
« Reply #11 on: November 08, 2015, 05:55:06 AM »
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Offline Enthalpy

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Re: Evidence of ions
« Reply #12 on: November 09, 2015, 09:33:31 AM »
And how should we tell whether Na and Cl are ionized in solid NaCl? Is this question any answerable?

Since every Na is surrounded by Cl atoms that "touch" it, and the electron shells are fuzzy, I don't quite see how we should tell that an electron belongs to Cl rather than Na. It's the same locations except at a few small positions.

But it does make more sense in BaTiO3 and SrTiO3, where Ba and Sr are not completely surrounded but have an eccentric position - or rather, two possible positions, which make these crystals piezoelectric, ferroelectric, and at the proper BaxSr1-x composition versus the temperature, gives them a huge permittivity. For these compounds, Ba and Sr do carry a (partial) charge, whose effect is observable by the strong polarization of the solid.

BaTiO3 and SrTiO3 being strongly nonlinear (they make the type II ceramic capacitors for electronics design) one could observe the saturation polarization, and from the atom movement, infer the partial charge. I stilll haven't done it and would be interested if someone did.

Same for less symmetric crystals like quartz which is piezoelectric. There we can tell that the bond is polarized.

And what about water, with its permittivity of 80? Its polarization results from molecule orientation, for which accurate models exist. Obviously H and O carry a partial charge. Should we call water an ionic compound because of this? No. It's better to say that bonds are more or less polarized.

Offline AdiDex

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Re: Evidence of ions
« Reply #13 on: November 17, 2015, 02:32:17 AM »
And what about water, with its permittivity of 80? Its polarization results from molecule orientation, for which accurate models exist. Obviously H and O carry a partial charge. Should we call water an ionic compound because of this? No. It's better to say that bonds are more or less polarized.

I think that there is no sharp boundary between an Ionic Bond And a Non-Ionic Bond but that does not means we should ignore this classification. On broad level there is a clear distinction . The Polarization in the bond of NaCl is quite large(It means that Electron Probability Density is quite large in the neighborhood of Cl )  so it should be defined as Ionic Bond .

Offline AdiDex

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Re: Evidence of ions
« Reply #14 on: November 17, 2015, 02:50:41 AM »
Since every Na is surrounded by Cl atoms that "touch" it, and the electron shells are fuzzy, I don't quite see how we should tell that an electron belongs to Cl rather than Na. It's the same locations except at a few small positions.

Whenever there is interaction between 2 waves , they looses their individuality  . So there is no question about the belonging of that electron to the Na or Cl . It was the question about Electron Probability Density .

And I think This question is answerable if it is in the context of the Electron Probability  Density .

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