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Topic: Chromate Ion- covalent or ionic?  (Read 6494 times)

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Offline ShadowSpirit

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Chromate Ion- covalent or ionic?
« on: April 15, 2007, 08:16:59 AM »
Hi, I'm new around here and it's only my first year to take Chemistry so excuse me if I ask some stupid questions.

I remembered that polyatomic ions are supposed to be covalent compounds, but in a chromate ion, there is chromium, which is a transition metal, so it can't be covalent (since covalent bonds are between non-metals), right? Also, I can't figure out the structure of chromate ion.

Thanks very much.

Offline f4cepl4nt

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Re: Chromate Ion- covalent or ionic?
« Reply #1 on: April 15, 2007, 02:33:54 PM »
Hahahah ok, this may be a bit beyond the scope of the class you're taking, but -

Every compound is not purely ionic or covalent, and each has what's called an 'ionic character'. This is figured out using the electronegativity difference of the atoms in the molecule.

In this case, Chromium has an electronegativity of 1.66, and Oxygen is 3.44.

3.44 - 1.66 = 1.78, which is just BARELY considered ionic, chromate's bonds are just 54% ionic.

As for the structure of chromate, that one is a bit tricky. I was able to sketch one out, but it was butt-ugly and I don't think it's right at all. So I guess you'll have to wait for someone else to answer that part hahahah...but with chromiums 3d sublevel with 5 electrons, maybe they're somehow used in the bonds? Because one measly 4s electron for 4 oxygen atoms with 2 holes in each 2p sublevel to fill doesn't seem to cut it.

I wouldn't worry about the structure though - you'll probably never have a need to know it anyway. ;D

Offline ShadowSpirit

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Re: Chromate Ion- covalent or ionic?
« Reply #2 on: April 16, 2007, 04:40:59 AM »
I did a search on electronegativity and I think I understand more about covalent and ionic bonds now. Thank you so much. ^_^

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