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SO, I stumbled upon a periodic table of electronegativity-

http://www.thecatalyst.org/electabl.html

Now I don't understand why the first 3 noble gases have blank spaces instead of the electronegativities.

If it is because their octet is complete then why doesn't the noble gases Kr, Xe and Rn have blank spaces under them?

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They don't have values there because they aren't on the pauling scale of electronegativity, as they don't form any compounds with other elements. However, argon and neon can technically form compounds with other elements; it is just extremely unlikely. For example there is a compound called Argon Fluorohydride, HArF, that can exist, but is only stable at around 27K (-246C). I don't think Helium can form any compounds other than with itself. The other noble gases also can react with fluorine (As well as other elements), and make slightly more stable compounds. Hope that helps :)

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  • $\begingroup$ then why does Krypton, Radon and Xenom have an electronegativity value? They are noble gases too so they shouldn't be electronegative. $\endgroup$ – MartianCactus Jul 24 '16 at 8:25
  • $\begingroup$ Noble gases have their outer s and p orbitals filled with electrons (just s in case of He). Beginning with Argon, they also have unfilled inner (d, f) orbitals, which allows them to accept electrons, even if it's unlikely they do. $\endgroup$ – Guntram Blohm supports Monica Jul 24 '16 at 8:49
  • $\begingroup$ @GuntramBlohm you said beginning with argon. Then why doesn't argon have an electronegativity? $\endgroup$ – MartianCactus Jul 24 '16 at 9:47
  • $\begingroup$ @adi maybe because with argon the outer d orbitals are not as good electron acceptors as their counterparts in the heavier atoms? We do know of at least ine argon compound (en.wikipedia.org/wiki/Noble_gas_compound), but argon lacks the broader empirical base in which we can establish a well defined electronegativity. Such a database has been developed with compounds of krypton and heavier ng's. $\endgroup$ – Oscar Lanzi Jul 24 '16 at 13:56

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