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Help needed (confused with certain points on syllabus) watch

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    Ok so im doing ccea, i have my exam tomorrow..

    Could anyone shed some light on these concepts mentioned in my syllabus??

    • use sigma and pi bonds to explain relative bond strength(ok with this) and relative bond lengthof the c=c bond

    • comment on variation of boiling points of Halogenoalkanes

    • does OH thermal stability decrease down group II??:eek3:

    • I always learnt the reaction of
      Al3+
      Mg2+
      Zn2+
      with Aq. Ammonia. but it says the reaction with NaOh and aq ammonia to distingish? is syllabus right? and if so is there a difference with NaOh and without.
      The colourless solution forms white ppt.. etc etc.


    Ah honestly, if anyone has any idea about these.. it would be soo helpful...

    Im panicing...:eek3:
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    First point:

    A single bond is formed by a sigma interaction, which is the overlap of two s orbitals. If two atoms which have formed a sigma bond also have two p orbitals which can overlap, they form a pi bond as well as the sigma bond, which gives you your double bond. The p orbitals of the two atoms point up and down rather than towards each other so the two carbon atoms must move slightly closer together to maximise the pi overlap.

    Second point:

    As you lengthen the carbon chain, you have more electrons, meaning the van der waals forces get stronger so the boiling point increases. As you go from Cl --> Br --> I, the halogen is getting larger, so again, more electrons, stronger van der waals interactions and higher boiling point. You might also be thinking "but the electronegativity difference gets smaller so the dipole-dipole interactions get weaker". This is true, but the C-Cl (for example) bond is just one bond and considering you'll have a hydrocarbon chain there as well, the Van der Waals forces are a greater factor.

    Third point:

    Answered in another thread of yours.

    Fourth point:

    I'm afraid I don't remember the colours of these from when I did them at school. Sorry :o:
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    (Original post by MedAmy)
    Ok so im doing ccea, i have my exam tomorrow..

    Could anyone shed some light on these concepts mentioned in my syllabus??

    • use sigma and pi bonds to explain relative bond strength(ok with this) and relative bond lengthof the c=c bond

    • comment on variation of boiling points of Halogenoalkanes

    • does OH thermal stability decrease down group II??:eek3:

    • I always learnt the reaction of
      Al3+
      Mg2+
      Zn2+
      with Aq. Ammonia. but it says the reaction with NaOh and aq ammonia to distingish? is syllabus right? and if so is there a difference with NaOh and without.
      The colourless solution forms white ppt.. etc etc.


    Ah honestly, if anyone has any idea about these.. it would be soo helpful...

    Im panicing...:eek3:
    for part 4, refer to attachment.
    Attached Images
  1. File Type: pdf qualitative analysis.pdf (46.1 KB, 199 views)
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    (Original post by Kyri)
    First point:

    A single bond is formed by a sigma interaction, which is the overlap of two s orbitals. If two atoms which have formed a sigma bond also have two p orbitals which can overlap, they form a pi bond as well as the sigma bond, which gives you your double bond. The p orbitals of the two atoms point up and down rather than towards each other so the two carbon atoms must move slightly closer together to maximise the pi overlap.

    Second point:

    As you lengthen the carbon chain, you have more electrons, meaning the van der waals forces get stronger so the boiling point increases. As you go from Cl --> Br --> I, the halogen is getting larger, so again, more electrons, stronger van der waals interactions and higher boiling point. You might also be thinking "but the electronegativity difference gets smaller so the dipole-dipole interactions get weaker". This is true, but the C-Cl (for example) bond is just one bond and considering you'll have a hydrocarbon chain there as well, the Van der Waals forces are a greater factor.

    Third point:

    Answered in another thread of yours.

    Fourth point:

    I'm afraid I don't remember the colours of these from when I did them at school. Sorry :o:
    ah thank you soo much *** you wee star** lol
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    (Original post by shengoc)
    for part 4, refer to attachment.
    woohoo thanks so much xoxoxo
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    (Original post by MedAmy)
    ah thank you soo much *** you wee star** lol
    Haha, you're welcome.

    (Original post by shengoc)
    for part 4, refer to attachment.
    That looks like a really good reference page. Very clear.
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    That looks like a really good reference page. Very clear.[/QUOTE]

    yeah, got that from cambridge igce chem exam paper.
 
 
 
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