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Chemistry Paper 4-theory- doubts =D

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acer4me

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Khalifa said:
Hi guys. Can someone please tell me why first electron affinity is exothermic while the second one is endothermic?
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Well khalifa..
U see; 1st is either exo or endo
But 2nd electron affinity is ALWAYS endo.. why? Because u are adding an extra electron...it might mean u are adding an extra shell ...that requires alooot of energy to overcome the repulsion that already occurs between negative electrons..
:D inshallah my answer is clear to u bro !
 
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acer4me

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nishan2052 said:
please tell me why different grp r attached at different place in benzene ring?
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Nishan :


Some groups are called electron donating and others are called electron withdrawing

Electron donating groups include CH3- , OH-
Electron withdrawing include COOH , NO2

However idk whether NH2 is EW or ED
Can anyone help plz?

Electron donating activate 2, 4, 6 positions on benzene ringh for othr grps to b attached
Electron withdrawing activate 1, 3, 5
 
kelly sheers

kelly sheers

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acer4me said:
I researched. .its electron donating group. .bcz of itz lone pair
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yes sorry It does withdraw electrons from its third bond, but at the same time the high electron density around the N (it has a lone pair) feeds back into the bond, causing the overall effect to be activating (electron donating). Compare this with -NO2, which is deactivating-the lone pair doesn't exist any more since both "lone" valence electrons are now used in double bonds with oxygen. Then the electronegativity of N does cause deactivation. therefore electron donating
 
D

donorsolutions

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kelly sheers said:
yes sorry It does withdraw electrons from its third bond, but at the same time the high electron density around the N (it has a lone pair) feeds back into the bond, causing the overall effect to be activating (electron donating). Compare this with -NO2, which is deactivating-the lone pair doesn't exist any more since both "lone" valence electrons are now used in double bonds with oxygen. Then the electronegativity of N does cause deactivation. therefore electron donating
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plz can u explain the mechanism in this question 3 c(iii) . i am having trouble understanding it is this thing even in our syllabus ??
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_42.pdf
 
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