Nobel Gases (Zero Group)

The p-Block Elements Nobel Gases (zero group) * Ramsay and travers [1898] [Helium, Neon, PRELUDE Krypton and Xenon] * Zero group of group–18 contains six gaseous elements He, Ne, Ar, Kr, Xe and Rn. They carried out fractional distillation fo liquid argon * First five elements are present in small quantities in under reduced pressure. From the first fraction they atmosphere and as such called rare gas. isolated Helium and Neon. By further fractional * Radon is obtained by the dins integration of radium distillation they had isolated Krypton and Xenon. and is radioactive. * Dorn [1900] [Radon] * Due to stable outer configuration of s2p6 (octet) these Radon is a dis integration product of radium. gases exhibit inert character and are called inert 226  Rn222 + He4 86Ra 86 2 gases. * Under specific conditions, these gases can form * Jansen ascertained the presence of helium in the sun by spectroscopic analysis. compounds [XeF2, XeF4 etc.]. These gases are referred as noble gases, ISOLATION Electronic configuration of noble gases : There are two methods employed to isolate noble Element Electronic Configuration gases commercially. Helium [He2] Is2 (1) Fractional distillation of liquid air : Neon [Ne10] [He] 2s2, 2p6 Since the noble gases have the boiling points quite Argon [Ar18] [Ne] 3s2, 3p6 far apart. Hence fractional distillation is easily Krypton [Kr36] [Ar] 3d10, 4s2, 4p6 employed. Xenon [Xe54] [Kr] 3d10, 5s2, 5p6 Claude’s apparatus : This is used for the Radon [Rn86] [Xe] 4f14, 5d10, 6s2 6p6 manufacture of liquid O2 and N2 where noble gases * These element occupy position between most are obtained as by – products. electronegative (halogens) and the most First fraction : [He, N2] electropositive (alkali metals) elements. Thus zero The mixture of gases is passed through a spiral cooled group elements are neither electropositive nor in liquid nitrogen. In this process most of the nitrogen electronegative in nature. condenses while He and Ne passes out. This mixture * Helium has stable s2 (duplex) configuration. Because is cooled in a rectifying column (low temperature of duplex and octet configuration they show zero containing liquid H2) where neon solidifies. Helium valency. still remains in the gaseous state escapes out. DISCOVERY OF NOBLE GASES Note : N2 is removed from He by CaC2 * Ramsay and Rayleigh [1894] [Argon] : CaC2 + N2  CaCN2 + C It was found that the density of atmospheric nitrogen Second fraction : [Ar, O2] was 0.5% higher than that obtained by chemical methods. They isolated this gas from air by passing Mixture of Ar and O2 is passed through spiral tube over heated copper to remove oxygen and then cooled by liquid nitrogen. In this process most of nitrogen by passing over heated magnesium. the oxygen is liquefied and argon with a little bit of 2Cu + O2  2CuO 3Mg + N2  Mg3N2 oxygen escapes out. The vapour density and atomic weight of the gas Note : O2 is removed from Ar by heated Cu was found to be 20 and 40 respectively. The gas 2Cu + O2  2Cu was named Argon. The p-Block Elements Third fraction [Kr, Xe] Argon : This fraction is evaporated whereby the residual liquid (i) Used for creating inert atmosphere for welding. becomes richer in Kr and Xe. The separation of Kr (ii) Ar plus He mixture is used for signal electrical device. and Xe is then becomes easier as they have wide difference in their boiling points. (iii) Ar plus Ne are used in filling fluorescent tubes, radio–valves etc. (iv) Used in bulbs to enhance the life of filament. USES OF NOBLE GASES Krypton and Xenon : Used in filling up bulbs containing incandescent filaments. Helium : Radon : (i) Used in radio therapy of cancer. (i) Used in balloons and airships as it is light and non- (ii) Used to check the defects in steel sheets. inflammable. (ii) Used in creating inert atmosphere in metallurgy and EXAMPLES welding metals. (1) Who obtained an inactive gas by heating the mineral clavate with dil. H2SO4. (iii) Used in filling tungsten lamps required for signaling. Hilledbrand (iv) A mixture of He and O2 is used for respiration by (2) ow the discovery of rare gases has affected the divers in deep sea. Since He is much less soluble in theoretical development of chemistry give two the blood than nitrogen at high pressure. evidences. (v) Used for filling vacuum tubes and radio tubes. (i) Periodic table [Rare gases have been placed (vi) Used for producing low temperature (–269ºC) Neon : between alkali metals (most electronegative). (ii) Discovery of isotopes : Neon isotopes where first to be separated. (i) Neon lamps are used in green houses as it is effective (3) Asthma patient use for respiration a mixture of : Helium + Oxygen in the growth of chlorophyll. (ii) Neon lamps ar used in botanical gardens. (iii) Neon lights are visible in fog and mist and there fore neon lights are used for making signals in night for pilots. (iv) Neon is also used in discharge tubes required for decorative and advertising purpose. (4) Maximum heat of vaporizations associated with ............. inert gas Xenon 178ºC (5) Xe + O2F2  ............. + O2 the unknown product is : XeF2 (6) Formula of xenonoxy – tetra fluoride is XeOF4