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Which of the following pairsof elements wouldhavemorenegativeelectron gainenthalpy ? Explain (i) Nor O(ii)s or O(iii) C or Si |
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Answer» SOLUTION :(i) Theelectron gainenthalpy ofO ishighlynegativewhilethatof N isslightly positive. Reason . The electronicconfigurationof N isquitestable`(1s^(2) 2s^(2) 2p^(1)_(x) 2p_(x)^(1) 2p_(z)^(1))` sinceit hasexactly half-filled2p-orbitaland hencehas notendencyto acceptan EXTRA electron. Inotherwordsenergyhas tobe suppliedto addan extra electron .Thuselectron- gainenthalpy of N isslightly positive . Incontrast the electronic CONFIGURATION of O `(1s^(2) 2s^(2) 2p_(x)^(2) 2p_(x)^(1) 2p_(z)^(1))` is not sostablebut ithas highernuclearchargeand loweratomicsizethan Nandhenceit hasa hightendency to acceptan extra electron . Inotherwordselectron gainenthalpyof Ois highly negative . (ii) S hasmorenegativeelectron gainenthalpy than O Reason . The sizeof O ismuchsmallerthanthatof S. Asa resultthe electron- electron replsionsin thesmaller 2p- subshell of O arecomparatively largerthan thosepresent in thebigger 3p- subshellof s. Therefore, Shashighertendency to acceptan additionalelectron than O (iii) C hasmorenegativeelectron gainenthalpy than Si Reason. this is because C- atom hassmallersizeSi- atom (NOTE that theelectron - electron repulsions in these ATOMS are notverylargebecausetheycontainonly 4 electrons in theoutermostshell) |
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