The Periodic Table

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1:33 AM

@orthocresol I guess I meant that I like spectroscopy in general as a field because the theory is applied in a way that's often more directly linked to experiment, but I'm really interested in XAS these days.

2 hours later…

1,3-feeds

3:57 AM

Q: Tagging questions on diffraction of things other than X-rays?

The question What is “detwinning” as a 2D crystallography technique? and neutron diffraction brought this to mind, but electron diffraction is an established technique as well, and there may be others. For the linked question I chose "compromise tagging" and left the comment there is no neut...

4 hours later…

Hot nitric acid (HNQ)

8:25 AM

Q: Why isn't 'chemically-strengthened glass' made with potassium carbonate? To begin with?

Instead of making potassium-strengthened glass by creating ordinary soda-lime glass first, then replacing the sodium atoms/ions with potassium by putting the glass in a bath/solution of potassium nitrate, why not replace the 'soda' (sodium carbonate) in the initial process(es) with potassium carb...

materials glass

9 hours later…

YUSUF HASAN

5:52 PM

Hello, I was just told a rationale for the higher boiling point of stibane than ammonia, when in fact, the melting point of ammonia is higher than stibane due to H-bonding..(So I just wanted to run it by you guys)...It was said that in the liquid and gaseous phase(the point when we talk about boiling point)...Ammonia undergoes amine inversion quite rapidly..Hence the H-bonds formed are also broken easily, and so, thw H-bonding loses it's effectiveness..While at the freezing point..

Molecular movements are restricted..Hence effective H-bonding can occur here..So the effect of H-bonding dominates..Is this correct? @Mithoron @Loong @orthocresol @Zhe ?

Mithoron

I don't think so

YUSUF HASAN

@Mithoron It seemed logical to me..Can you please tell where is the flaw in this reasoning?

Mithoron

While h-bonds are broken and reformed all the time, most of the time the bond in present (BTW don't use so many ellipsys)

YUSUF HASAN

@Mithoron Okay sure( I have a habit of using ellipsis XD), but if the bond is getting broken, then doesn't it weaken the overall strength of the H-bond?

@Mithoron Also, if this rationale is incorrect, then can you please suggest a better one?

Mithoron

Time average - actually how long are both periods (bound/unbound) is important. Also similar analysis of vdW for stibane would be important

And don't ping too much ;>

YUSUF HASAN

6:07 PM

Ok sorry again. I don't come by in this group too much :( , And this time average thingy would fall under the domain of computational chemistry it seems..Is there anyway to see this anomaly qualitatively?

Mithoron

I don't think it's anomaly

Melting and boiling point are quite different. In melting packing of molecules is important

YUSUF HASAN

So..How should I go about to look at the packing in ammonia and stibane?

Mithoron

Crystal structure is needed

Q: Why is the boiling point of stibane higher than that of ammonia?

I recently came across the fact that the boiling point of $\ce{SbH3}$ (stibane) is greater than that of $\ce{NH3}$ (ammonia). I was expecting $\ce{NH3}$ to have a greater boiling point as a consequence of intermolecular hydrogen bonding. I understand that as molecular mass increases, van der Waal...

inorganic-chemistry periodic-trends boiling-point hydrogen-bond

YUSUF HASAN

Ohh.. Okay, thnx!

Mithoron

A: Why is the melting point of hydrogen iodide larger than that of hydrogen fluoride?

The increase in dispersive attraction between HI molecules is greater than the loss of dipole interactions. Only in $\ce{H2O}$ do dipole forces dominate (Intermolecular and Surface Forces, Jacob N. Israelachvili). Contribution of dispersion to intermolecular bonding for various molecules: $\ce{...

dipoles are important too. I think in practice unless you have much serious data one could speculate on and on, and pick out many effects and get no closer to facts

3 hours later…

Bounty Hunter

9:38 PM

Q: Do symmetric hydrogen bonds in neutral molecules exist?

As far as I know, there have only few truly symmetric hydrogen bonds been observed. Unquestionable is the existence of it in the bifluoride ion, $\ce{[F-H-F]-}$, see also here. There are a couple of more, like in a water hydroxyl complex $\ce{[HO\bond{~}H2O]- @Cu($110$)}$,[1] or in the hydrogen d...