Physical properties of noble gases
Noble gases are nonmetallic, monoatomic ,odorless, colorless, inert gases . The noble gases include helium, neon, argon, krypton, xenon and radon(radio active), are located in Group VIII of the periodic table. They are called as inert gases because they have extremely low chemical reactivity.
Electronic configuration of noble gases
The general electronic configuration of these elements is ns2np6, they have completely filled ,stable octet valence shell configurations hence they are inert, have high ionization energies and zero electron gain enthalpy.
They are also called as rare gases because they are present in very low concentrations as gases in air and they are not found combined with other elements. The abundances of the noble gases in the universe decrease as their atomic numbers increase. Helium is the most common element in the universe after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe is helium-4, and is believed to have been formed during the Big Bang. Large amounts of new helium are being created by nuclear fusion of hydrogen in stars.
So far, no compound of He, Ne and Ar has been reported. Xenon forms some compounds with fluorine and oxygen. This is because of the noble gases have very little tendency to lose electrons due to their high ionisation enthalpies. Therefore, these gases can only combine with the elements which are highly electronegative with favourable electron gain enthalpy (or electron affinity). It is for this reason that most of the compounds of noble gases are with fluorine and oxygen.
The noble gases neon, argon, krypton and xenon can be obtained by condensation of air and fractional distillation, where as Helium is obtained by fractional distillation of natural gas. Radon is produced by the radioactive decay of radium–226, found in uranium ores.
The elements form low boiling liquids, the boiling points decreasing rapidly with the decrease in molecular mass. As the atomic mass increases , the weaker van der waal forces between the atoms increases down the group in noble gases.
Neon gas glows with an orange–red color in discharge tube
The main use of noble gases is due to their chemical inertness and low boiling points. All noble gases find use in Lasers. Important uses of the noble gases are:
Helium is used in gas–cooled atomic reactors as a heat transfer gas, Neon gives a orange–red glow in electric discharge tubes, argon is used in thermionic tubes, krypton is used in filament lamps and radon is used in the preparation of ointment for the treatment of cancer and other diseases.