Paul will enjoy this:

[url=https://phys.org/news/2019-04-elusive-molecule-universe-space.html]Elusive molecule, first in Universe, detected in space[/url] | PhysOrg: Helium hydride, HeH[sup]+[/sup].

[QUOTE=ewmayer;514062]Paul will enjoy this:

[url=https://phys.org/news/2019-04-elusive-molecule-universe-space.html]Elusive molecule, first in Universe, detected in space[/url] | PhysOrg: Helium hydride, HeH[sup]+[/sup].[/QUOTE]Yup.

It's widely believed, and even taught by chemistry teachers/professors who should know better, that helium doesn't form chemical compounds. In reality, it doesn't form any (known to be stable) electrically neutral chemical compounds. He[sub]2[/sub][sup]+[/sup] is another example of a stable but reactive and ionic molecule.

Most chemists are remarkably cavalier when it comes to distinguishing between stabilty and reactivity. Two examples from my DPhil research are CeO and Cu[sub]2[/sub], neither of which are generally regarded as stable compounds because they don't exist at room temperature and pressure.

[QUOTE=xilman;514063]Most chemists are remarkably cavalier when it comes to distinguishing between stabilty and reactivity. Two examples from my DPhil research are CeO and Cu[sub]2[/sub], neither of which are generally regarded as stable compounds because they don't exist at room temperature and pressure.[/QUOTE]
F <--this.

[QUOTE=Uncwilly;514064]F <--this.[/QUOTE]
¿Que?

Mon-atomic neutral Florine
Does/can it exist? Does it exist in nature?

[QUOTE=Uncwilly;514096]Mon-atomic neutral Florine
Does/can it exist? Does it exist in nature?[/QUOTE]I'm not a chemist, but from everything I've heard about fluorine, if a neutral fluorine atom were somehow coaxed loose, it wouldn't be around for long if there were anything nearby for it to latch on to. Isolating fluorine [i]molecules[/i] was quite a challenge, finally met by the French chemist Moissan.

I'm no chemist, so it occurs to me to wonder -- assuming you had a way to (try to) isolate some neutral fluorine atoms, how would you detect their presence?

[side note] BTW, Moissan has a mineral named after him, Moissanite. Chemically, it is silicon carbide. Its occurrence in nature is associated with meteor strikes.

Silicon carbide is produced industrially as an abrasive, known as Carborundum. It is now also produced in large pure crystals as a gemstone. Its hardness, high refractive index and dispersion, and relatively low cost compared to diamond, make it one of the real innovations in the gem business. [/side note]

[QUOTE=Dr Sardonicus;514114]I'm not a chemist, but from everything I've heard about fluorine, if a neutral fluorine atom were somehow coaxed loose, it wouldn't be around for long if there were anything nearby for it to latch on to. Isolating fluorine [i]molecules[/i] was quite a challenge, finally met by the French chemist Moissan.[/QUOTE]Monatomic fluorine certainly exists in nature, in stellar atmospheres for instance, and can be made quite easily in the lab by dissociating F[sub]2[/sub] by (for example) heating or photolysis. Actually, the photolytic reaction is a particularly useful method for producing monatomic fluorine in the lab.

As noted it is extremely reactive and will readily re-dimerize unless the temperature is high enough or there is nothing else around with which to react. AFAIK, it doesn't react with helium, whether the latter is solid, liquid or gaseous. I doubt that it reacts with PTFE either and many other fluorides.

Studying it is straightforward by the standard techniques of atomic spectroscopy.

[QUOTE=xilman;514124]Monatomic fluorine certainly exists in nature, in stellar atmospheres for instance, and can be made quite easily in the lab by dissociating F[sub]2[/sub] by (for example) heating or photolysis. Actually, the photolytic reaction is a particularly useful method for producing monatomic fluorine in the lab.[/quote]
I'd seen this on line, but alas it wasn't clear to me whether this was [i]neutral[/i] F or F[sup]+[/sup]. In particular, I noted the use of monatomic fluorine in "plasma ashing." My understanding is that "plasma" and "neutral" are incompossible...

[quote]Studying it is straightforward by the standard techniques of atomic spectroscopy.[/QUOTE]Ahh. My guess would be that the spectrum of neutral F would differ from that for F[sup]+[/sup]. Is that right?

[QUOTE=Dr Sardonicus;514128]I'd seen this on line, but alas it wasn't clear to me whether this was [i]neutral[/i] F or F[sup]+[/sup]. In particular, I noted the use of monatomic fluorine in "plasma ashing." My understanding is that "plasma" and "neutral" are incompossible...

Ahh. My guess would be that the spectrum of neutral F would differ from that for F[sup]+[/sup]. Is that right?[/QUOTE]A plasma can be electrically neutral (equal numbers of oppositely charged entities) or may contain an admixture of unionized species.

The spectra are indeed very different. F+ is isoelectronic with neutral O.

[QUOTE=xilman;514136]A plasma can be electrically neutral (equal numbers of oppositely charged entities) or may contain an admixture of unionized species.[/quote]
I've heard of various [i]occupations[/i] being unionized, but not species! This forum is a cornucopia of information...

Seriously, though -- as soon as I saw [i]unionized[/i] in your post, I thought of Isaac Asimov's essay [i]To tell a chemist[/i]. He proposed two questions to tell a chemist from a non-chemist:
[quote](1) How do you pronounce UNIONIZED?

(2) What is a mole?[/quote]

I can certainly see a plasma being neutral overall. I can also imagine some neutral atoms or molecules floating around in a plasma, even though it is often described as "ionized gas."

The use of monatomic fluorine for "plasma ashing" reminded me of something that was mentioned in my high school chem class -- the "atomic oxygen torch." If memory serves, the torch was fed with atomic oxygen, i.e. disassociated oxygen molecules. The energy used in the disassociation was energy that was [i]not[/i] being sapped from the combustion process, making for a hotter torch.

[quote]The spectra are indeed very different. F+ is isoelectronic with neutral O.[/QUOTE]As far as electrons go, yeah, that makes sense. The greater nuclear charge may twiddle things a bit, but my guess is, [i]only[/i] a bit.

[QUOTE=Dr Sardonicus;514140]As far as electrons go, yeah, that makes sense. The greater nuclear charge may twiddle things a bit, but my guess is, [i]only[/i] a bit.[/QUOTE]You guess correctly.