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     The elements are:   Helium (Z = 2),  Neon (10),  Argon (18), Krypton (36), Xenon (54) and Radon (86).

        As per our normal rules of electronic configurations and explained properties, noble gases have a valence of 0.  They shells are all filled with paired electrons in all energy states possible.  There is no energy state available to get a new electron.    Neither the nucleus allows an electron to go out.  The ionization energy is very very high.  They are inert and do not react with other elements in the periodic table.  They are single atom molecules.   It is found not long ago that they too form compounds.   At least some of them do.

       The electrons in Helium are held closely to the nucleus as it is a very small atom.  In Radon the outermost electrons  are in the principal quantum number : n =  6.  That is very far.  The radius of atoms increase proportional (roughly for an idea) to square of n.   Thus the outermost electrons are loosely bound as compared to Helium.  So its ionization energy is less.

       A few hundred compounds of noble gases have been discovered/invented/formed in the laboratories In the last two decades.   Xenon, Krypton and Argon show very small reactivity.  Their reactivity is in the order of  Ne < He <  Ar < Kr < Xe < Rn.     Due to radioactivity, Radon does not actually form as many compounds as Xenon.   Many decades ago in 20th century, scientists including Linus Pauling have postulated and predicted regarding the compounds of Noble gases.  A lot of research went into these.   At very low temperatures, the compounds exist with more stability.

       Some compounds with Helium and Neon are formed, but they are not neutral and very stable.  Existence and formation of Xenon Octa Floride Xe F8,  Xenon Hexafloride Xe F6 and  Kripton hexa Floride Kr F6 are predicted with logical explanations and conditions.   As Foride is the most electronegative element, it can make these elements react.  These compounds are thermodynamically (energy wise) and kinetically unstable.   Some compounds with Oxygen too are observed.

     Xenon can exist in the oxidation states of  +2, +4, +6   or +8.  So  Xe F2, Xe F4, Xe F6, Xe O4,  Sodium perxenate:  Na4 (Xe O6)  are formed in the laboratories.   The equation of Xenon Florides is:
            Xe  + n * F2  => Xe F_2n

       Xenon Floride is available in the market.  It is used as a fluorinating agent, where deficiency of Fluorine is there or to furnish Fluorine in a reaction.   We can form compounds with Xenon and Carbon,  Xenon bonded to Nitrogen element, Oxygen, Chlorine, Gold Mercury and Xenon too.

     Some compounds with other elements are formed at low temperatures (below zero deg. C).       Due to high Radioactivity of Radon, it is less reactive (as opposed to general prediction) than Xenon.  Radon floride and Oxides are formed.

     Krypton is found in oxidation state 2 in many compounds.  Kr F2 is most common.   Krypton forms compounds with Nitrogen and Oxygen that are stable at temperatures below -60 deg. C.

     Helium has been found to form  :  He H+ ion.   Argon Floride (Ar F) and Krypton Floride Kr F exist in excited electronic state.  They are used in ultraviolet lasers  in performing surgeries and some fabrication.

     Under very high pressure and low temperatures, Carbon compounds with Noble gases can be formed.

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