Zero group consists of six elements, helium, neon, argon, krypton, xenon and radon. All of theses are inert and inactive gases at ordinary temperature. All of them except radon (nitron) are present in atmosphere although in very small quantities.
Thus, they are also known as rare gases of the atmosphere. Under special conditions, inert gases form a few compounds also and hence are also known as noble gases.POSITION IN THE PERIODIC TABLEThese elements were unknown at the time of Mendeleef and he could not imagine any element devoid of chemical activity and thus, left no space for them in his periodic table. First of all, Julio Tomson in 1896 proposed that a new group (zero) should be included in the periodic table.
According to him, there should be six elements in this group with atomic weights 4, 20, 36, 84, 132 and 212. Based on this thought, Ramsay and Trovers discovered the inert gases in the atmosphere and thus, a new group was introduced in the periodic table. The group has been inserted between highly electronegative halogens (VIIA) and highly electropositive alkali metals (I-A).
ELECTRONIC CONFIGURATIONHej = lv2Ne10 = lr2;2y2,^<5arlg is2;2s2,2p6;3s2,3p6kr36 is2;2s2,2p6;3s2,3p6,3d10-,4s2,4p6xe54 is2;2s2,2p6;3s2,3p6,3d10;4s2,4p64d10;5s2,5p6rn86 is2;2s2,2p6;3s2,3p6,3d10;4s2,4p6,4d10,4f4;5s2,5p6,5d10;6s2,6p6alloftheseelementshavens2,p6structureoftheiroutermostshell(exceptinghe,whichpossessesonlyonecompleteshell,i.e.,ly2).thusallofthesegaseshaveastableoutermostshellandtheirinclusioninthesamegroupoftheperiodictableisjustified.thispositionisjustifiedbythefollowingfacts:
Ramsay showed its existence on earth. In fact Ramsay was in search of some new source of argon. Miers suggested that Ramsay might investigate mineral clevite for argon. Ramsay and Trovers heated clevite with dil. H2S04 in vacuum and collected the evolved gas. This gas was sent to Crookes for spectrum analysis.
The spectrum contained the £>3 line observed by Frankland and Lockeyer. Thus, the presence of helium on earth was established.Discovery of Other inert GasesRamsay and Travers obtained the other gases of this group by fractional distillation of argon obtained from atmospheric air. These gases were named as neon (new), krypton (hidden) and xenon (stranger). Radon or nitron was discovered by Dorn (1900) as disintegration product of radium.ggRa226-» 86Rn222 + 2He4
The physical constants of these gases are given in the following table.These are all inert, colourless and odourless gases. '(ii) They are all monoatomic.(iii) They are liquified with great difficulty and the boiling point of helium is very close to absolute zero.(iv) They all have specific heat ratio (Cp/Cv) equal to approximately 1 • 66.(v) This group comes in between highly electro-positive alkali metals and highly electro-negative halogens group.(vi) These are all inactive, however, helium forms some very unstable compounds.