The Periodic Table

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5:02 PM

@barlop Yes, see e.g. pubs.acs.org/doi/10.1021/acs.joc.8b02740

Well, to be technically precise, your sentence contradicts itself. If there is an electronegativity difference, then the electrons are not truly equally shared: one bonding partner (the more electronegative one) has more electron density than the other. I assume you meant a covalent bond, as opposed to an ionic bond.

barlop

@orthocresol thanks,, could you quote me which sentence it was that you refer to, where I had the error, to which you are addressing?

ah I see the sentence.. i see it links to it

@orthocresol yes I understand it better now.. there's equal sharing of electrons when there is no electronegative difference. Then when there is some small electronegative difference there is unequal sharing of electrons.. (like H2O), still considered covalent but some partial charges.. polar covalent. And with more electronegative difference like >1.7 then there's transfer of electrons.. and it's considered ionic

orthocresol

5:46 PM

@barlop Not really, it doesn't jump to suddenly being completely ionic if the difference is larger than 1.7. It's a smooth spectrum ranging from perfectly equally shared to complete transfer.

This guideline of "more than X difference is ionic" is very crude and IMO, not useful. Dunno why it still gets taught.

barlop

thanks.. What is the molecular formula for sodium chloride in gas, liquid and solid.. i'm curious how they differ? (or do they differ at all?)

orthocresol

It's the same.

Physically they are different things, but the formula doesn't change.

barlop

@orthocresol I spoke to a phd guy and he said this it's maybe a bit too much to paste but i'll link to it here gist.githubusercontent.com/gartha1/… i'll try to paste it here mayeb it's not too much to paste

so he said "A molecule of NaCl (one sodium ion plus one chloride ion) is electrically neutral. It qualifies as a molecule just as much as a molecule of carbon monoxide. But for sodium chloride, molecules only exist in the gas phase."
"

and "In the solid phase (and in the liquid phase to the best of my knowledge), sodium and chloride ions are not paired up and do not form discernible molecules of NaxClx. In in the gas phase they do, as this is lower-energy than separate gas-phase ions. My knowledge of the literature of this is not large, but I have heard that gas phase sodium chloride consists of molecules of Na2Cl2.

Likewise, sodium chloride in the gas phase consists of molecules, and (I’m told) they have a particular structure and composition. A molecule of Na1Cl1 will be quite different than a molecule of Na2Cl2. In th…

orthocresol

Ok, I mean, that might be true, but I'd argue it's overcomplicating things. You don't need to know that much detail.

barlop

well, I do want to know..

orthocresol

5:58 PM

Then you can check the literature. There will probably be papers discussing the structure of gas-phase NaCl and whether it forms (NaCl)_x aggregates.

barlop

ok..

When it comes to the term "molecular formula" does that apply to compounds that are classified as ionic compounds too?

Is there a better term than molecular formula? (that somebody won't say ah you can't say that for an ionic compound)

orthocresol

Q: What is the difference between a Chemical Formula and Formula Unit?

In my textbook, a chemical formula is described as : "A formula that shows the kinds and numbers of atoms in the smallest representative unit of a substance" While a formula unit is described as : The lowest whole number ratio of ions in an ionic compound. Thus the formula unit for sod...