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    Hi peeps,

    Got a quick question about what you need to know for the oxidising abilities for group 7 elements for the AQA CHEM2 exam at AS.

    The specification says: understand that the ability of the halogens (from fluorine to iodine) to oxidise decreases down the group (e.g. the
    displacement reactions with halide ions in aqueous solution)

    Yet the official Nelson Thornes AQA endorsed book just says that you need to know F->I- in terms of oxidising ability and that that's the trend. This doesn't even mention *why*.

    chemguide online states there's a 'faulty' explanation about electron affinity - ie. as the atoms get bigger, new electrons find themselves further from the nucleus and there's more shielding (overrides stronger nuclear attraction). Bigger atoms are less good at attracting new electrons.

    It then goes on to talk about the 'proper' explanation, stuff about the fact that the halogens occur diatomically and these have to be split before they can gain electrons. On top of that it goes on about isolated ions becoming wrapped up in water molecules to form hydrated ions.

    I have a third source, a Collins Student Support book which got me an A in my first unit telling me (essentially) the same thing.

    Finally, my teacher says we just need to stick to the 'faulty' explanation but I'm really unsure as the specification isn't clear. I don't know what I need to be able to regurgitate because these books and sites are all catered for the AQA syllabus. Obviously they're just going slightly more in depth, but I can't judge from the spec. if that's necessary.

    I suppose I should just learn it all anyway?
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    (Original post by AdamskiUK)
    Hi peeps,

    Got a quick question about what you need to know for the oxidising abilities for group 7 elements for the AQA CHEM2 exam at AS.

    The specification says: understand that the ability of the halogens (from fluorine to iodine) to oxidise decreases down the group (e.g. the
    displacement reactions with halide ions in aqueous solution)

    Yet the official Nelson Thornes AQA endorsed book just says that you need to know F->I- in terms of oxidising ability and that that's the trend. This doesn't even mention *why*.

    chemguide online states there's a 'faulty' explanation about electron affinity - ie. as the atoms get bigger, new electrons find themselves further from the nucleus and there's more shielding (overrides stronger nuclear attraction). Bigger atoms are less good at attracting new electrons.

    It then goes on to talk about the 'proper' explanation, stuff about the fact that the halogens occur diatomically and these have to be split before they can gain electrons. On top of that it goes on about isolated ions becoming wrapped up in water molecules to form hydrated ions.

    I have a third source, a Collins Student Support book which got me an A in my first unit telling me (essentially) the same thing.

    Finally, my teacher says we just need to stick to the 'faulty' explanation but I'm really unsure as the specification isn't clear. I don't know what I need to be able to regurgitate because these books and sites are all catered for the AQA syllabus. Obviously they're just going slightly more in depth, but I can't judge from the spec. if that's necessary.

    I suppose I should just learn it all anyway?
    There are conflicting answers because it is A-level!!!! They don't teach you the real thing, just a simplified version!!!!
    The real process will be a complex summation of many reaction enthalpies, such as the atomisation, breaking the X-X bond, electron affinity, solvation and desolvation enthalpies etc.
    I would suggest learning the intermediate explanation (the one about the electron affinities of the halogens).
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    (Original post by AdamskiUK)
    Hi peeps,

    Got a quick question about what you need to know for the oxidising abilities for group 7 elements for the AQA CHEM2 exam at AS.

    The specification says: understand that the ability of the halogens (from fluorine to iodine) to oxidise decreases down the group (e.g. the
    displacement reactions with halide ions in aqueous solution)

    Yet the official Nelson Thornes AQA endorsed book just says that you need to know F->I- in terms of oxidising ability and that that's the trend. This doesn't even mention *why*.

    chemguide online states there's a 'faulty' explanation about electron affinity - ie. as the atoms get bigger, new electrons find themselves further from the nucleus and there's more shielding (overrides stronger nuclear attraction). Bigger atoms are less good at attracting new electrons.

    It then goes on to talk about the 'proper' explanation, stuff about the fact that the halogens occur diatomically and these have to be split before they can gain electrons. On top of that it goes on about isolated ions becoming wrapped up in water molecules to form hydrated ions.

    I have a third source, a Collins Student Support book which got me an A in my first unit telling me (essentially) the same thing.

    Finally, my teacher says we just need to stick to the 'faulty' explanation but I'm really unsure as the specification isn't clear. I don't know what I need to be able to regurgitate because these books and sites are all catered for the AQA syllabus. Obviously they're just going slightly more in depth, but I can't judge from the spec. if that's necessary.

    I suppose I should just learn it all anyway?
    I just think it is sometimes hypocritical to know that certain theories/explanations are with flaws, yet for simplicity, they are often adopted as the norm explanations.

    By all means, if you are not going to do chemistry at higher levels, i suppose you can be happy with the "faulty" explanation. However, if you are going to do chemistry at higher levels, then it'd be better if you could understand the "proper" reason too.
 
 
 
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