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Topic: Is iron(III) oxide ionic or covalent?  (Read 2862 times)

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Offline PicturesOfLilly

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Is iron(III) oxide ionic or covalent?
« on: November 26, 2020, 06:56:46 AM »
I know that the answer depends on whether your reference uses 1.7 or 2 as an electronegativity difference, but I'm still a little confused beyond that.

If the iron atom in Fe2O3 has a +3 charge, which means it's an ion. So therefore you'd think the molecule is ionic. But apparently it can be argued to be covalent. I would have assumed that the partial charges associated with polar molecules are willy nilly in comparison to the forces between oppositely charged ions. At the end of the day the electrons are either being shared, or they are not being shared. I thought it was black or white when it came to covalent or ionic.

I also have another question about salt dissolving in water. Given that polar molecules only have a partial charge, I don't see how the tiny polar E.N charges on H2O molecules would be strong enough to pull apart NaCl bonds, when salt is dissolved in water? Think anyone else have this thought when they were first given the explanation of the important of polarity for dissolving things? This was the first thing I thought of when shown a diagram of H2O molecules lining up around a NaCl crystal lattice unit.

Offline Borek

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Re: Is iron(III) oxide ionic or covalent?
« Reply #1 on: November 26, 2020, 07:50:02 AM »
I thought it was black or white when it came to covalent or ionic.

Nope. Both "ionic" and "covalent" are idealized concepts, every bond/compound lies somewhere in between.

That is, assuming that "ionic" and "covalent" are the only classification possibilities.
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Offline PicturesOfLilly

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Re: Is iron(III) oxide ionic or covalent?
« Reply #2 on: November 27, 2020, 06:34:25 PM »
I thought it was black or white when it came to covalent or ionic.

Nope. Both "ionic" and "covalent" are idealized concepts, every bond/compound lies somewhere in between.

That is, assuming that "ionic" and "covalent" are the only classification possibilities.
Well that's great but it doesn't explain anything.

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Offline PicturesOfLilly

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Re: Is iron(III) oxide ionic or covalent?
« Reply #4 on: November 29, 2020, 05:36:08 PM »
You don't seem to like reading textbooks. Maybe the internet?
https://www.chemteam.info/Bonding/Electroneg-Bond-Polarity.html#:~:text=The%20rule%20is%20that%20when,the%20bond%20is%20considered%20ionic.&text=If%20the%20electronegativity%20difference%20(usually,the%20bond%20is%20nonpolar%20covalent.

Thanks for the link. I read it, but it didn't address the area I'm confused with. My own text book also didn't seem to make clear the fact that nearly all molecules behave both as ionic and covalent. I think that was all I was confused about.

When Borek said "every bond/compound lies somewhere in between" ionic and covalent, I thought I had him with the example of O2... thinking that the (2-) ions would repel each other. But of course O2 is purely non polar so the ion don't exist. But take the example of the molecule BCl3. It is a covalent molecule of course. But seeing as it can also be considered ionic (as Borek said above), then each Cl atom can also be considered to have a (1-) charge. So that would have to mean that the Boron atom is also acting as a (3+) ion? Is that the case?


Offline Borek

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Re: Is iron(III) oxide ionic or covalent?
« Reply #5 on: November 29, 2020, 07:12:48 PM »
You are trying to describe something that is grey as either black, or white.
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Offline PicturesOfLilly

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Re: Is iron(III) oxide ionic or covalent?
« Reply #6 on: November 30, 2020, 06:27:42 PM »
You are trying to describe something that is grey as either black, or white.
You seem to lack empathy.

But I have a question for about salt dissolving in water. Given that polar molecules only have a partial charge, I don't see how the tiny polar E.N charges on a H2O molecule would be strong enough to pull apart ionic NaCl bonds? Did you have this thought when you were first given this explanation for why salt dissolves in water?

Offline AWK

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Re: Is iron(III) oxide ionic or covalent?
« Reply #7 on: December 01, 2020, 12:45:48 AM »
Enthalpy of dissolution of NaCl is only 3.9 kJ/mol, hence lattice dissociation enthalpy is only slightly greater than the hydration enthalpy of the ions.
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Offline PicturesOfLilly

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Re: Is iron(III) oxide ionic or covalent?
« Reply #8 on: December 02, 2020, 05:50:34 AM »
Enthalpy of dissolution of NaCl is only 3.9 kJ/mol, hence lattice dissociation enthalpy is only slightly greater than the hydration enthalpy of the ions.
But the ionic bonds are stronger than the dipole force that a water molecule may exert on the salt, is weaker than the ionic forces between Na and Cl. Therefore I don;t see how how the salt would be pulled into solution.

Offline AWK

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Re: Is iron(III) oxide ionic or covalent?
« Reply #9 on: December 02, 2020, 06:17:11 AM »
Thinking like that won't get you anywhere.
From the crystal structure of NaCl, the ionic bond is actually 6 electrostatic interactions. As an ion goes into solution, each ion surrounds 4 to 6 water molecules - the weaker interaction, but there are ~ 10 of these interactions per stoichiometric unit of NaCl. And as a result, we have such a negligible value of the heat of dissolution that we practically do not notice any decrease in the temperature of the solution when dissolving NaCl (except for physical chemists using special tools).

But if you mix snow or ice with solid salt, you better not try to touch this mixture with your hand because the temperature may be slightly below -20°C. This lowering of the temperature is mainly due to the energy needed to destroy the ice crystal lattice, not NaCl.
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Offline PicturesOfLilly

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Re: Is iron(III) oxide ionic or covalent?
« Reply #10 on: December 02, 2020, 12:17:35 PM »
Thinking like that won't get you anywhere.
Well that's the whole idea of asking the question... so that I will no longer think of it in the way that "won't get [me] anywhere", and then I might actually get somewhere!

So the ionic bonds, although stronger, are outnumbered. Great

Offline Borek

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Re: Is iron(III) oxide ionic or covalent?
« Reply #11 on: December 02, 2020, 01:04:58 PM »
Well that's the whole idea of asking the question... so that I will no longer think of it in the way that "won't get [me] anywhere", and then I might actually get somewhere!

Not if you ignore answers given
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