Noble Gases Make Bonds
(Or, at the very least, they can)
This is (almost) verbatim text from a chemistry unit project I did in Grade 12, and I still think it holds up, so I’m putting it up here. Damn, I was so funny back then. I miss the version of me that was willing to be so cheeky on assignments.
WARNING:
This report may contain:
- Cynicism
- Tangents
- A flippant tone
- Extreme points of view
- Signs of Authorial madness
Continue at your own risk.1
Introduction
There are seven noble gases in existence: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). That being said, oganesson is really bad at existing. We know it’s radioactive, but other than that we essentially have no idea what its physical and chemical properties are because only a few atoms of it have been observed. At any given moment, probably only a few oganesson atoms exist, if any, since synthetic elements break down really easily. Because of this, I’m going to ignore the existence of oganesson.
It’s irrelevant.
So as I was saying, there are six noble gases. Other names for this family are the rare gases or the inert gases, except that both of these names are lies. Most of us were taught in school that noble gases don’t react with anything very much in the same way that we learned that energy levels in atoms can only hold up to eight electrons. Most of the things people learn in school are explanations that are oversimplified to the point of being incredible inaccurate. Sometimes, though this is rare, this will be because the teacher is not aware of the “truth”. However, in many cases the lie is easier to teach and to understand. No matter how far from the actual “truth” it might be.
I use quotes here for the word “truth” here because many scientists say they do their research for the sake of finding some kind of truth. But as far as I know, science isn’t very good at coming up with truths. The closest things we have to truths in science are ideas that large groups of scientists agree on for now. Of course, they’re not always able to consider the possible exceptions, because they don’t have the knowledge to predict them. So then weird data happens, and it clashes with the accepted idea, and now the scientists have to reconcile the weird data with the idea. Sometimes the data really is just an exception. But sometimes it can’t be explained, so an entirely new idea arises that can also explain the gaps left behind in the old one, which is now a confirmed lie. Sometimes the lie will continue to be taught to eager, truth-seeking students in order to increase “clarity” and “ease of comprehension”, which are noble intents. However, they do not excuse the fact that the students are being taught a lie. Some of them will grow up and never learn any better as adults. Is that what we want? A misinformed society?
But I digress.
A lot of scientists used to teach that noble gases are completely inert. I’m sure many of them completely believed this. Or course, they must have had reasons to believe this, but considering how many things get disproven in science, these men (and perhaps women, though I’m sure no one cared about the women) should have known better.
Please excuse me for a moment while I call them idiots.
There are no absolutes in science.
Noble Gases?
Technically, the first noble gas was discovered in 1785 by Henry Cavendish, but since he didn’t seem to care about the existence of the substance he’d stumbled upon and didn’t bother to isolate or name it, no one cares that he was involved . (Well, maybe they do care… but I don’t.)
The two people who actually discovered the first noble gas were Lord Rayleigh and Sir William Ramsay, who agreed to pursue their research together in 1894. Rayleigh had discovered that atmospheric nitrogen was about 0.5% denser than the nitrogen found in chemical compounds, and thought there might be an unknown gas hiding in there. In order to isolate the mysterious gas, Ramsay and Rayleigh combined the atmospheric nitrogen with red-hot magnesium, forming magnesium nitride (Mg3N2). What was left was a gas that wouldn’t combine with anything, including fluorine. To the disbelief of a few critics, the two scientists announced the new element to the Royal Society in 1895. They called it argon, from the Greek word for idle, αργός (argos).
In fact, Sir William Ramsay discovered or had a hand in discovering most of the noble gases. He even won a joint Nobel Prize for it. Hooray.
Scientists believed that the noble gases couldn’t form bonds because the electrons were organized in such a way that the valence shell always contained eight electrons. According to the prevailing bonding theory of the time, an octet of valence electrons was the most stable electronic arrangement for any atom. All atoms tried to achieve this octet through bonding, whether this involved an exchange of electrons or sharing of electrons. Since the noble gases had theoretically already achieved this stable octet, they would not bond with other elements.
Of course, despite now knowing that the “octet rule” is a massive oversimplification that doesn’t have as much to do with bonding as we thought it did, we still teach it in high schools. Grade nine and ten students do not learn that some compounds are stable with less than an octet, that some compounds are stable with more than an octet, or that noble gases make bonds. What’s more, recent research has found that sometimes bonds are not required for the formation of compounds, but we don’t teach that either. Cutting-edge research is never taught even when it’s true. This is for the sake of clarity, of course.
So of course, we feed students lies.
The scientists were right about one thing, at least—most noble gases are quite reluctant to form bonds and only do so under very controlled, and sometimes extreme, conditions. Most importantly, they don’t burn. This is actually useful—if it were not for the existence of helium, hot-air balloons would probably explode. If it weren’t for argon, light bulbs probably wouldn’t last very long.
Noble gases usually don’t bond. But that doesn’t mean they won’t.
Modern techniques can force elements to do some pretty wacky things.
Bonds? How?
Are you still a sceptic? Do you still believe noble gases shouldn’t be making bonds? Well, turns out I exaggerated a little bit in the previous sections. Okay, maybe I exaggerated a lot.
Before I explain the discovery of noble gases, it is important to know that noble gases do, in fact, have stable electronic configurations. Typically, elements react with other elements because their electronic configurations are in some way unstable. So how do we get noble gases to react? By making them unstable. How do we make them unstable? By pulling some electrons away from them.
This is called oxidation, by the way.
Oxidation is what occurs when one atom (or compound) strips electrons from another atom (or compound) and keeps them. You heard that right—it’s a complete transfer of electrons. Reduction is what occurs when one atom (or compound) gives electrons to another atom (or compound). The two always happen together.
Oxidation gets its name from oxygen because it was the first known oxidizing agent. Oxygen, perhaps unsurprisingly, is very good at oxidation. For some reason, it really likes to eat electrons. Rusted car? That’s oxidation. Wine goes bad? That’s oxidation. Burning? That’s oxidation. Do you see a trend here? Oxygen is hardly ever the element losing the electrons.
So imagine how surprised Neil Bartlett and Derek Lohmann must have been when they found a compound that could oxidize oxygen. Research papers are typically written in an impartial manner, so I guess we’ll never know. But I think it’s safe to assume no small amount of shock was involved.
Noble gas compound research began as an accident. Okay, that’s not exactly true. Noble gas compound research began with scientists trying to react noble gases with fluorine and destroying lab equipment in the process. However, they all failed, so I don’t care about them, though I’m sure they were very important people. So as I was saying, noble gas compound research began as an accident. Neil Bartlett had been experimenting with fluorine and platinum in a lab at the University of British Columbia, where he taught chemistry. Somehow, he accidentally produced a deep red solid, but couldn’t determine its exact chemical composition. In 1961, he and Derek Lohmann, his graduate student, found out that the compound was formed when platinum hexafluoride (PtF6) reacted with oxygen, creating O2+PtF6-.
What’s weird here is that the oxygen ions have a 2+ charge, which hardly ever occurs—oxygen tends to oxidize, not reduce. This meant PtF6 must be a powerful oxidizing agent. Since oxygen and xenon have similar ionization energies, (1165 kJ/mol and 1170 kJ/mol respectively), Bartlett thought PtF6 might be able to oxidize xenon as well, even though this task was considered “impossible”.
In March 1962, Bartlett decided to test his hypothesis by combining PtF6, a red gas, with xenon, a colourless gas, inside a glass apparatus. The reaction took place at room temperature and a yellow-orange precipitate was formed. The compound was first identified as xenonfluoroplatinate (XePtF6), or later, [XeF]+[PtF5]-. Bartlett tried convincing his colleagues that he had created the world fist noble gas compounds. Alas, many of them were idiots and chose not to believe him.
Most of the noble gases can be coaxed into forming compounds, nowadays—even helium can form compounds. According to some extremely cutting edge research, helium can actually combine with sodium under extreme conditions to form Na2He. Under high pressure, most noble gases become more reactive —xenon reacts with oxygen and magnesium reacts with xenon, krypton, and argon, for example.
Due to thermodynamics (and math I am not yet qualified to explain), sodium and helium are more stable as Na2He than as mixtures of elemental sodium and helium at pressures greater than 160 GPa (gigapascal). When the two are sufficiently compressed, the high pressure forces out the valence electrons in the sodium, which causes all of the sodium atoms to become cations. Helium then locks around the Na+ ions and groups of 2 electrons, making it very difficult for the charges to move. In this manner, the material becomes stable.
The Compounds
Now that we are several years further into the future than Bartlett was, we can make a whole bunch of different noble gas compounds. Most of the known xenon compounds contain fluorine and oxygen—they form the most stable compounds with xenon due to their high electronegativities. These groups of compounds are known as xenon fluorides (XeF2, XeF4, XeF6), oxyfluorides (XeOF2, XeOF4, XeO2F2, XeO3F2, XeO2F4) and oxides (XeO2, XeO3 and XeO4).
Xenon difluoride (XeF2) features a central xenon atom that has undergone sp3d hybridization. The compound is stable, has a linear structure, and has the VSEPR formula AX¬2E3. It is also dangerous as it decomposes on contact with light or water vapour.
It’s pretty important to note here that when I say something is stable, I mean that it’s thermodynamically stable, as in, the compound will not spontaneously decompose. This does mean that the compound is stable in the colloquial sense. Xenon difluoride is very unstable and very reactive, especially with water, which means it needs to be protected from air. Xenon tetrafluoride (XeF4) features a central xenon atom that has undergone sp3d2 hybridization. Xenon tetrafluoride has a square planar structure (VSEPR formula AX4E2). The compound is stable and is a colourless crystal.
Xenon hexafluoride has a distorted octagonal shape for reasons I don’t understand, involving 6 bonding pairs and a lone pair. (The jury is still out on whether Xenon is undergoing sp3d3 hybridization or not hybridizing at all.) It’s a colourless solid, but it sublimates into yellow vapours somehow, which is wack. Fluorine is the only element that can directly react with Xenon, due to its extreme electronegativity. Xenon fluorides can be formed by combining xenon gas with fluorine gas, heating the two to very high temperatures, and hoping nothing explodes.
Xenon oxides are formed through the hydrolysis of Xenon halides, since oxygen will not directly react with xenon. For example, Xenon difluoride reacts with water to form xenon trioxide (which is extremely explosive when dry) and hydrogen fluoride.
Xenon can apparently also bond with gold, which is also supposed to be an inert metal (LibreText). Some noble gas compounds actually have uses; for example, xenon difluoride is used to etch silicon. Argon, Krypton, and Xenon compounds are used in laser eye surgery.
However, most of them exist for the sake of scientists being able to say they exist.
A lot of science exists for the sake of existing.
Conclusion
It might be useful to note here that this report was put together by a high school student who definitely had better things to do.
None of this information is important. None of it matters. There is no reason for anyone to know this stuff. Except that it’s… cool.
The benefits of studying noble gas compounds are mostly that chemists get to play God and make chemicals do stuff they were probably never intended to do. Oh, they also gain a lot of valuable insight about how extreme conditions affect reactivity, how we may be able to store noble gases in the future, how oxidation works, how different compounds can form, and so on…
But really, no one cares except for a very small group of chemists. Which means this isn’t important.
This also means that this report solely exists for the purpose of earning me a non-failing grade. What a fun thought.
I guess I’ll leave you on that.
Bibliography
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Chemistry of Xenon (Z=54). In: Chemistry LibreTexts [Internet]. LibreTexts.org; [cited 2019 Oct 27] Available from: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_18%3A_The_Noble_Gases/Z%3D54_Chemistry_of_Xenon_(Z%3D54)
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