57

As other answers have noted, the only gas lighter than helium is hydrogen, which has some flammability issues that make it more difficult to handle safely than helium. Also, in practice, hydrogen is not significantly "lighter" than helium. While the molecular mass (and thus, per the ideal gas law, the density) of hydrogen gas is about half that of helium, ...


48

Actually, hydrogen is the only gas that is lighter than helium. However, it has a very big disadvantage: It is highly flammable. On the other hand, helium is almost completely inert - this is why it is very much safer to use the latter. What might happen when you use hydrogen instead of helium was impressively proven by history when the "Hindenburg" ...


41

TL;DR Xenon hexafluoride has a fluxional structure in the gas phase, with multiple rapidly interconverting conformers. The three most important conformers have $C_\mathrm{3v}$, $O_\mathrm{h}$, and $C_\mathrm{2v}$ symmetries. The minimum energy conformer is probably $C_\mathrm{3v}$. Experimental evidence The structure of xenon hexafluoride ($\ce{XeF6}$) has ...


22

Noble gases usually do not form strong bonds between their atoms - it takes fair amount of energy to dimerise them into excimers, but those are short-lived excited molecules. Thanks to excitation, shells of the atoms aren't closed and they react, but very quickly they lose energy and become separate atoms. On the other hand there are many stable molecules ...


21

When the temperature of helium gas is decreased to about 5.2 K, a phase transition to ordinary liquid helium ($\ce{He}$ I) occurs. The behavior of this liquid phase is normal and identical to any other liquid phase. As temperature is decreased more (at moderate pressures), helium does not solidify. In fact, it undergoes a phase change to a second liquid ...


19

The melting and boiling points of noble gases are very low in comparison to those of other substances of comparable atomic and molecular masses. This indicates that only weak van der Waals forces or weak London dispersion forces are present between the atoms of the noble gases in the liquid or the solid state. The van der Waals force increases with the ...


19

No, this is not possible. Actually, if I would have to think of the most unlikely chemical conceivable, that would be it. Let's see why: Krypton is a noble gas that doesn't bond to anything. All of the known krypton compounds can be counted on one hand, and most of them contain fluorine. Putting krypton in a large molecule like this just can't be. This is ...


19

Inert gaseous components such as methane and argon are indeed should be eliminated from the system in order not to lower the partial pressure of the reactants too much. Technically there is usually a standalone gas separation plant where the extraction of argon from the recycle gas is performed basically using modified Linde process [1 , pp. 428–430]. ...


18

Chemist Neil Bartlett in 1962 discovered that Xenon although a noble gas, is able to form compounds with other substances even though it is chemically "inert". Neil Bartlett at the time in 1961, produced an unidentified red solid and discovered that the red solid was a reaction between, gaseous flouride, platinum hexafluoride (PtF6) and oxygen that was ...


17

$\ce{XeF8}$ is not known to exist though O.N is +8. Why is this so? At least 2 compounds have been reported that contain the $\ce{XeF8^{2-}}$ unit. See, for example: $\ce{(NO^+)2[XeF8]^{2-}}$ (reference) Metal salts of the form $\ce{(M^{+})_2[XeF8]^{2-}}$ where M is a metal salt such as $\ce{Cs, Rb}$ (see the above reference) or $\ce{Na}$ (see p. 62 in ...


15

Why do Krypton and Xenon have high electronegativity? As you point out, krypton ($\ce{Kr}$) and xenon ($\ce{Xe}$) are members of the Noble gas family. They are generally unreactive (noble) because all of their occupied orbitals are filled with electrons - they really don't want to gain or lose an electron. However, in the 1960's researchers found that $\...


14

If Xeon does not react with any other chemical, how does this happen, from a chemical point of view? If molecules of phospholipids do not react with each other, how do they form biomembranes? If Xenon doesn't react, how can it form host-guest complexes with cryptophanes? It's not necessary to form covalent or ionic bonds to hold the pieces together. Weak ...


14

Of course you can take all the electrons off an atom - it is then called "fully stripped" in atomic physics. You don't need to do it to an entire mole, mind you. In accelerators one would send energetic neon ions through a background gas or a thin foil, and the interactions will result in various charge states coming out, up to and including fully stripped.


13

Actually it is not necessary to dig deep into quantum mechanics. There are several reasons why noble gasses are stable (as gasses at room temperature). First of all, there is the obvious full valence shell. Trend in the periodic table make clear that the charge of the nucleus grows from left to right in every period. The attractive force towards the ...


12

The reason that we discovered more fluorides of Xeon than Helium, Argon, and Krypton is quite obvious and you might already know it. As lighter noble gases have more stable shell configuration, it is more difficult to make any kind of compound, including fluorides. Also, the higher amount of fluorine atoms in a molecule of the compounds means drawing more ...


11

Yeah, dimers of noble gas atoms are stable due to dispersion aka London forces. More generally, neutral, non-polar molecules can still form very weak bound states arising entirely from the induction and interaction of instantaneous dipole moments (that is, fluctuations in the electron density around an atom arising from the motion of electrons). My ...


11

A compound needs to have an overall neutral charge. The formula has a -5 charge so it is not a compound. The supposed 2-d structure has a -20 charge and therefore doesn't correspond to the formula.


11

$\ce{XeF_6}$ can't be stored in glass as it reacts with the silica that makes up the glass $\ce{2XeF_6 + SiO_2 -> 2XeOF_4 + SiF_4}$ This can proceed further to eventfully make $\ce{XeO_3}$: $\ce{2XeOF_4 + SiO_2 -> 2XeO_2F_2 + SiF_4}$ $\ce{2XeO_2F_2 + SiO_2 -> 2XeO_3 + SiF_4}$ Dry $\ce{XeO_3}$ is highly explosive ... That is why both $\ce{...


9

Yes, hydrogen is lighter than helium but helium, on the other hand, is an inert gas (very less reactive). Also, hydrogen is highly flammable so that would make it unsafe to play with balloons.


9

Liquids and solids form because intermolecular forces hold together different molecules/atoms/ions/biscuits in a strong enough fashion to prevent them from drifting away from each other. In a very basic sense you could say that gases are non-ordered, liquids have near-range ordering but not far-range, and solids are well ordered into crystal lattices. Noble ...


9

According to Heats of Formation of XeF3+, XeF3-, XeF5+, XeF7+, XeF7-, and XeF8 from High Level Electronic Structure Calculations Inorganic Chemistry 2010, vol. 49, pages 261–270: Unlike the previously studied XeF2, XeF4, and XeF6, $\ce{XeF8}$ is predicted to be thermodynamically unstable with respect to loss of $\ce{F2}$, and the reaction is ...


9

One more No from a topological standpoint. There is no known molecular structure of this topology (assuming any bond any any atom, preserving connectivity only). The closest one would be some derivative of existing benzo[1,2:4,5]dicyclobutene [1]: Also, tetraoxo-manganese unit bound in a shown fashion suggests a coordination polymer (e.g. neither a ...


8

The reason why noble gases form molecules is because of London forces, which are very weak. The electrons in noble gas atoms are on the move all the time, so there will be a moment when they will spend more time in an area, which generates a temporary dipole and allows for interaction with another atom. An addendum regarding noble gas compounds in general: ...


8

Other answers have mentioned that dispersion forces are the key to answering the question but not how they increase from helium to radon (or let’s take xenon because that’s not radioactive so I feel safer breathing it). The larger the mass of a nucleus the more protons are in there, and the more protons in a nucleus the more electrons are around the outside....


8

First - in chemistry there's technically no such thing as bare multivalent cation, second - as you think, there's no such energetic chemical reaction, third - ionisation energy is physical property (although important for chemistry) and ..."is usually measured in an electric discharge tube in which a fast-moving electron generated by an electric current ...


8

When I think about such structure, I draw all valence electrons around the atoms and connect them somehow reasonably. There are two ways to connect the hydrogens to xenon. Either directly bonded as H-Xe bonds, which for me does not feel right here, or as part of OH groups, which also make more sense in the "acid" part. By connecting everything that way, you ...


7

The answer appears to be right there in the linked synthesis details - the nickel is non-catalytic and is only there to generate a passivated surface that won't degrade in the high-temperature fluorine atmosphere. [Edit] The plot thickens! this paper suggests that xenon may in fact abstract fluorine off the passivated nickel fluoride surface due to ...


7

Valence electrons have not much to do with this, as their outer shell is closed. As the other answer mentioned, dispersion forces are the ones responsible for any interaction between these atoms. The size dependence therefore is directly coming from the size dependence of dispersion forces: In a very simplistic way, a random charge fluctuation can ...


7

ArBeO and ArBeS are experimentally known. ArAuF, ArAgF and ArCuF are also experimentally known. CUOAr$_n$ and related complexes are known. ArBeNCN and ArBeNBO are predicted by theory.


7

As mentioned in other answers the dispersion force is responsible for noble gases forming liquids. The calculation of the boiling points is now outlined after some general comments about the dispersion force. The dispersion force (also called London, charge-fluctuation, induced-dipole-induced-dipole force) is universal, just like gravity, as it acts between ...


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