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I just Googled “the heaviest gas”
For sure, the first result (Radon) was wrong by a great margin
The second (WF6) was much closer to truth, but I decided to spend 10 minutes to check if Mother Nature knows anything heavier than that
Remind myself that refreshing dynamic programming or methods of clustering is much better for my career rather than chasing obscure gases
That quest was… addictive
Unexpectedly addictive
Sure enough, the further my search went, the stranger and stranger compounds I met, some clearly known only to a handful of people on Earth
Some were apparently so little known that I started seeing typos or errors in numerous “Dictionaries of This and That Compounds” that I dealt with
Clearly, I reached some very dusty fringes of the Forest of Gases
Yet every new chemical offered new ideas and challenged: “hey, can you find anything heavier than me that is still a gas?”
Like remodeling, this work could not be completed — but only stopped
Therefore, here is the list of some of the heaviest gases that exist in Nature
For the purposes of this article, a “gas” is any substance with a boiling temperature less than +20 C at normal atmospheric pressure, and stable enough at those conditions to measure that
“Heavier” simply means molecular weight
While that is not completely precise, I seriously doubt that anybody has ever made enough of some of these chemicals to determine their exact density in the gaseous form
With a molecular weight of 224 and a boiling point of 156 C [10], this is probably the heaviest gas containing Sulfur – 15x times heavier than a well-known SF6 and 78x times heavier than air
For sure, I would not recommend trying that with SF5C(O)CF3 — provided that you get enough of it somewhere, somehow
2 Let’s continue with N(CF3)2CF=CF2 (mw 233, bp 137 C, [20, page 648])
There is a whole industry dealing in these kinds of compounds
For application in aviation, they must have boiling points less than -40 C, and often have to contain Fluorine, Chlorine or Bromine, thus being rather heavy
Acceptance to this club is strongly restricted to only those chemicals that show no adverse health effects in humans
3 P(CF3)3 [mw 238, bp 173 C, (30, page 323]), AKA tris(trifluoromethyl)phosphine, is probably the heaviest gaseous phosphorus compound
Their molecular weights are the same 238, yet structurally they are different
One is Perfluorobutane, another Perfluoroisobutane, with the boiling temperatures of -17 C [50] and 0 C [60, page 6-70]
Theoretically, the speed of sound in that gas is only 119 m/s under normal conditions, that’s enough to turn 5th octave C into 3rd octave F# — provided that it won’t cause an unconsciousness via the anesthetic effect, of which I’m not sure
6 The next one is better be met only in a well equipped lab: Tellurium Hexafluoride TeF6 (mw 2416, bp
It is “a colorless, highly toxic gas with an extremely unpleasant smell” I always wondered – how do people know that?
7 Pentafluoroiodoethane CF3CF2I (mw 2459, bp 13 C, [80, page 424], [90])
Start with a good old ethane C2H6, replace one Hydrogen with Iodine and the rest with Fluorine
Listed as a potential anesthetic in [80], it probably is not poisonous – if knocking oneself out or overdosing does not count
8 Same applies to decafluorodiethyl ether C4F10O (mw 254, bp 0 C [80, page 413])
9 The next compound, perfluoropropyltrifluoromethyl ether CF3OCF2CF2CF3 (mw 254, bp 674 C, [20, page 650]) although seemingly belonging to the same family is listed as a potential fire suppressant
F5TeOF (mw 2576, “extrapolated” bp 06 C, [100, page 778])
Pretty much anything volatile with Tellurium in it is at least modestly harmful and does not smell welcoming
That applies to the next gas TeClF5 Tellurium (VI) chloride fluoride (mw 258, bp 135 C, [100, page 776])
Iodine heptafluoride IF7 (mw 2599, bp 48 C, [110])– a whole nine times heavier-than-air gas
Chemically reactive, dangerous
“Can cause fire on contact with organic material” Looking at its formula, one might get an idea: why don’t we substitute one Fluorine with something heavier, say Chlorine, and arrive to an even heavier IClF6?
Unfortunately, according to Wikipedia, there are virtually no interhalogen compounds featuring more than two halogens
WF6, a famous Tungsten Hexafluoride (mw 29783, bp 171 C, [120])
Wikipedia cautiously names it “one of the heaviest gases”, but provides no examples of anything heavier
For now, it suffices to say that WF6 is a well-studied chemical, used in semiconductor industry to deposit thin layers of Tungsten on Silicon
However, purchasing this gas for a home collection isn’t a good idea
Corrosive, poisonous and chemically active, it is better admired on a picture rather than in an ampule
At this moment, we are entering the realm of the Doubtland
The Doubtland
With a molecular weight of 29865, it is just 028% heavier than WF6
It definitely exists, as multiple sources suggest — see [130, page 61] or [140]
They both provide 191 C for its boiling point – so technically it should be a gas
Well, if you read the paper [140] (and I did), you’ll encounter the note that says: “The fluoride is also anomalous in that all of the other newly prepared compounds appear to be monomeric liquids or solids except (CF3)3GeF
As shown in Table 11, the sublimation point of this compound is normal in comparison with the other halides, but the melting point, 30 oC, is quite abnormal, about 125 oC above the melting point of (CF3)3GeCI
This shows extensive association in the solid state, probably by means of fluorine bridging between germanium atoms” And the article’s boiling point of 191 C is “extrapolated”, with the melting point given of 27-30 C
I am not exactly sure how to interpret that
Is that a solid, contrary to very volatile molecular Ge(CF3)3Cl (bp 37 C) and Ge(CF3)3Br (bp 49 C) ([130], [140])?
It would be great if anybody repeated the synthesis to verify the results obtained in 1975
It really feels strange to think if the molecule of Ge(CF3)3F was called into existence on Earth only once, by someone’s experiment 41 years ago…
Confusion is further enhanced by data sources like chemsrccom quoting a bp of +16 С for an even heavier compound Ge(CF3)3Cl But after cross-checking with other sources, I arrived to the conclusion that this is some kind of an error
Chmsrccom seems to list underestimated boiling points for many compounds (like 61 C for a monstrous Mo2((CH3)2N)6)
According to [130] and [150, page 22], it has a boiling point of -53 C, while being 132x heavier than WF6!
Many similarly structured but lighter compounds have much higher boiling points – such as Te(CF3)2 (mw 2656, bp 23 C, [160]), CF3-Se-Te-CF3 (mw 3445, “Orange oil
In comparison, it would be extremely strange for a heavier CF3-Te-Te-CF3 to be so more volatile than its lighter “close relatives”
Numerous wonderful errors exist across the literature (try searching (CF3)SbI2 for example), but at this point you may be wondering – are there any citizens of the Doubtland that are not typos?
Sure, there are
As much as the Doubtland can be confident, of course
According to [170], its predicted boiling point is around -40 C
With a molecular weight of 32297, that for sure would make it quite a strong candidate for the heaviest gas
Nobody has managed to synthesize that chemical yet
So in the end, we still don’t know whether PoF6 exists
And the question of “the heaviest gas” remains open, with the answer lost in fractal obscurity of exotic compounds known to only few experts…
Yet the story would be incomplete without a tour of the Almost Made It City, populated by numerous peculiar and curious compounds that were close to being heavier than Radon gases, but did not quite make it
Methylated metalorganics like W(CH3)6, Pb(CH3)4 (bp 100-110 C), or Sb(CH3)3 are often volatile
Of those with a mw over 222, the most volatile is probably dimethylmercury Hg(CH3)2
Described in [180] as “one of the strongest known neurotoxins”, this liquid with a bp of 93-94 C is certainly something to keep as far away from oneself as possible
Replacing Hydrogen with Fluorine in a CH3 group offers perfluoromethylated compounds like Bis(trifluoromethyl)selenium Se(CF3)2 (mw 217, bp
-2 C, [190, page 427]), N(CF3)3 (yes, another gas with bp of -6 C and mw of 221, [80, page 425]), or Te(CF3)2 (mw 2656, bp 23 C [200])
Most are volatile, and most are heavy – take a look at the liquid Pb(CF3)4 (mw 483, [40]) for example
Further substitutions produce an almost endless variety that was too vast to fully explore – like As(CF3)2Cl3 (mw 316, bp 94 C [30, page 325], or As(CF3)2H (mw 2139, bp 19 C [30, page 325]
I spent a great fortune of time looking at them
Sometimes it felt that the winner – a gas heavier than WF6 — was nearby
Yet in the end, the closest to breaking a records came Ge(CF3)4 with a mw of 3486 and bp of 317 C ([130], [140])
Still not a gas
Still I strongly suspect that a better candidate might be hiding somewhere amongst colorful varieties of trifluoromethyl substitutes, but I had to stop and attend my own life
PF3 can play a role similar to CF3, giving birth to volatile metal complexes
Of all them, the closest to being a gas is probably Ni(PF3)4 (mw 4107, bp 705 C, [230, page 1592])
Nickel appears to make the most low-boiling metal carbonyl — Ni(CO)4 with a mw 170, bp 43 C [240]
While other metal carbonyls are often volatile, too (like ReH(CO)5 or Os(CO)5) all of them appear to be solids or liquids
U(BH4)3(BH3CH3) is volatile but solid (mw 3112) per [250, page 554]
Other (even simpler) actinide borohydrides are less volatile
WF5Cl definitely exists but is “a yellow solid” [260, page 276], WF4Cl2 is “thermally unstable at room temperature, decomposing to tungsten hexachloride and tungsten hexafluoride” [270], and ReClF5 is “volatile red liq”, “Dec at rt and slowly at -30
Mp -2” (I love that language!) I found it in the same Dictionary of Inorganic Compounds edited by Jane E
Macintyre, but cannot provide you with the link because of the paywalls
Google simply does not return that page anymore (even if I search those exact terms), probably because I have already seen “too much” of that book without buying it
Org Chem
[20]: SEARCH FOR NEW FIRE SUPPRESSANT CHEMICALS, J
Douglas Mather, PhD Chemical Development Studies, Inc; Robert E
[30]: Fluorine Chemistry, Volume 2, edited by JH Simons
1989, 28, 981-982, page 981
[50]: Wikipedia on Perfluorobutane
[60]: CRC Handbook of Chemistry and Physics, 94th Edition edited by William M
[70]: Wikipedia on Tellurium hexafluoride
[100]: Chemistry of the Elements, By NNGreenwood, A
[110]: Wikipedia on Iodine heptafluoride
[120]: Wikipedia on Tungsten hexafluoride
[130]: F Perfluorohalogenoorgano Compounds of Main Group Elements
Compounds with Elements of Main Groups 1 to 5 (excluding N) and with S (partially)
Am Chem
Am Chem
Preparation and Stabilities of (Trifluoromethyl)germanium and (Trifluoromethyl)tin Compounds
[150]: Dictionary of Inorganic Compounds, Supplement 3, edited by Jane E
[170]: Monsanto Chemical Company, Unit 3 abstracts of progress reports, August 16–31, 1945: Summary of work to date on volatile neutron source
[180]: Wikipedia article on dimethylmercury
[190]: Advances in Inorganic Chemistry and Radiochemistry, Volume 3, Academic Press, Jan 1, 1961 – Science
[200]: Synthesis and Characterization of Volatile Trifluoromethyl Alkyl Tellurides, Douglas C
[200]: Synthesis and Characterization of Volatile Trifluoromethyl Alkyl Tellurides, Douglas C
[220]: Dictionary of Inorganic Compounds, edited by Jane E
Macintyre ($3,35700 at Barnes&Noblecom, holy beeps! )
[230]: Inorganic Chemistry By Egon Wiberg, Nils Wiberg
[240]: Wikipedia on Nickel Tetracarbonyl
[250]: The Chemistry of Uranium by JJ Katz, Eugene Rabinowitch
[260]: Halogen Chemistry, edited by Viktor Gutmann
[270]: Tungsten chloride fluorides: the preparation of cis- and trans-tungsten dichloride tetrafluoride and its decomposition into other tungsten fluorides, Journal of the Chemical Society A Inorganic Physical Theoretical · January 1970, G
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Table of Contents1 Which gas is the heaviest gas?2 Which is the first lightest inert gas?3 Which is lightest gas?4 Which is the heaviest gas on the periodic table?
Which gas is the heaviest gas?
Radon is the heaviest gas
It is a chemical element with the symbol Rn and atomic number 86
It is a radioactive, colorless, odorless, tasteless noble gas
The atomic weight of Radon is 222 atomic mass units making it the heaviest known gas
It is 220 times heavier than the lightest gas, Hydrogen
Helium is the lightest of the noble gases, and the second most abundant element in the universe; the Sun produces hundreds of millions of tonnes of helium every second
Which is the first lightest inert gas?
Which is the first lightest inert gas?
Neon is the lightest inert gas
Which is the lightest and heaviest gas?
Hydrogen is the lightest gas
Radon is the heaviest elemental gas with atomic mass of 222u
The heaviest gaseous molecule is of tungsten hexafluoride, WF6 with molecular mass of 29783 g/mol
Which is lightest gas?
Helium is the second most abundant element in the universe, after hydrogen
Helium has monatomic molecules, and is the lightest of all gases except hydrogen
Helium, like the other noble gases, is chemically inert
When was the heaviest inert gas found in the world?
This crossword clue Heaviest inert gas was discovered last seen in the January 13 2021 at the NewsDay Crossword
Which is the heaviest gas on the periodic table?
Inert gasses are located in the 8th group of the periodic table
Heaviest of the inert gases?
Radon is the heaviest of the inert gases
The inert gases are also known as the noble gases and are the lightest elements
True or false noble gases are inert gasses?
Which is the heaviest gas in the Solar System?
The divalent molecule is not the natural state of xenon in the Earth’s atmosphere or crust, so for all practical purposes, radon is the heaviest gas