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No Longer "Noble"; Argon Compound Found In Space
mbstone writes "Scientists at the University College of London — where argon was originally discovered in 1894 — have now found spectroscopic signatures of molecules of argon hydride (ArH), said to be produced via explosive nucleosynthesis in a core-collapse supernova in the Crab Nebula. The post-supernova molecular dust was observed by the Herschel Space Observatory shortly before it ran out of coolant in April.."
I don't get the connection between the title and the summary.
That far right side of the Periodic Table...where Helium, Neon, Xenon, Argon, and Radon live. Those elements have always been taught as being chemically inert (i.e. not able to be combined with any other elements), hence why they are called "noble" gases. This apparently is the first instance where that rule isn't necessarily true.
Do we categorize Argon as a non-noble gas, or do we redefine what a noble gas actually is?
Wait, I guess noble doesn't mean what I thought it meant, or there were already plenty of exceptions, as I just read this wiki article: https://en.wikipedia.org/wiki/Noble_gas_compounds
Only it's not; apparently compounds of the noble gases have been known for a while. The only thing there's no known compound of is helium. At least that's what one my chemistry friends is telling me.
Yeah, I had a sig once; I got bored of it.
But worth explaining for others that either didn't have chemistry class or maybe snoozed through it. The atoms of "noble" gases have their outer electron shell full so are very non-reactive, they usually don't make chemical bounds with other elements except under extraordinary circumstances requiring a lot of energy. Helium, neon, argon, and radon are probably the ones most people have heard mentioned at some time in daily life.
http://en.wikipedia.org/wiki/Noble_gas
This isn't even a compound, though. It's a molecular ion, ArH+. If you added an electron to it, it would fall apart, since ArH (neutral) is not bound.
A similar molecular ion exists for helium, HeH+. This ion is very important for the evolution of the early universe, since it can emit IR radiation to cool gas clouds, allowing stars to form from the nearly-pure H/He clouds that existed after the big bang.
Does this count? https://en.wikipedia.org/wiki/Helium_hydride_ion
Noble as in inert - it's not supposed to react to form a stable molecule.
Noble doesn't imply non-reactive, all of the noble elements can be ionized, with enough energy, just like any other element. What it means is they have a stable electron configuration. Helium, Neon, Argon, Krypton, Xenon, and Radon all have there outermost electron orbital shells filled. This means they're not inclined to give, borrow, or take electrons from other elements, this is why there called noble.
The fact that argon hydride was found in space implies that krypton, xenon, and radon hydride can also be found in space.
No, noble != inert
When I first learned about the elements many years ago, the description for those elements in the rightmost column was "inert". This means completely non-reactive.
Later on, when chemists made compounds of xenon, they realized the elements might not be so inert, after all. They gave the elements a new name: noble. They were not truly inert, but tended to have that tendency. Like other noble elements--such as gold or platinum--the elements in the rightmost column were disdainful of mixing with the hoi-polloi. It didn't mean they couldn't combine with other elements; they are just disinclined.
...you want to 1-up him you'll have to go for the quantum mechanic explanation of bonds. As far as *useful* models for chemical bonds go, even chemists use something pretty far from the "truth" . There are valence bond theory, orbital hybridization, resonance, and quite a few more.
When it comes to explaining nature, you use the model that is most USEFUL for what you want to explain, not for the most complicated one possible to impress your peers because you are so smart. :) That is why in many books atoms are still represented by red, white, blue "balls" and no one complains about it.
And by the way, the in the oxygen-hydrogen bond oxygen actually does sort of "borrow" the electron - the probability distribution for the location of that electron shifts towards the nucleus of the oxygen. That is why water molecules, while actually neutral (if not ionized), still act polar - the oxygen is essentially negative, the hydrogens positive. There is no equal "sharing".
Anything will combine with anything -- it just won't stay combined. You can rip as many electrons off (say) neon as you like, throw it in with another species, and watch them stick together long enough for neon to nab the electrons it wants -- but you won't get a compound that persists. Similarly, you can force xenon and anything together, but only a few pairings will produce compounds stable at even cryogenic temperatures.
The significant parts of this discovery are:
- a noble gas has been found in space (this confirmed people's expectations that argon-36 could be found as part of a supernova, even though argon-40 is much more common on Earth - note that argon-36 is also available on Earth, just in smaller quantities, it's not a new isotope)
- a noble gas molecule has been found in space (previously, argon compounds were only detected following Earth-based lab experiments)
The significant part of this discovery is not:
- that a noble gas can form a compound. Argon has had known compounds since 2003. Xenon has had known compounds since 1962, some of which are even stable at normal room temperature/pressure.
Actually, it's much more complicated. The gas Argon got its name from greek "argos", which means inert. The chemical group got the name of "noble gases" at the end of the 19th century from William Ramsay (Nobel prize in 1904). The first compound of a noble gas was discovered in 1962 by Neil Bartlett. Argon was the last noble gas for which a compound could be synthesized (2000).