doubts...

Discussion in 'Chemistry' started by rohIT, Mar 28, 2012.

  1. rohIT Registered Senior Member

    Messages:
    76
    I got a few doubts while reading Chem. thought i could ask you guys out :)

    1. do core electrons have a significant role in determining the properties of an element?

    2.what is the reason for inert pair effect?

    3. do bond dissociation energy and bond energy differ in magnitude? if yes, why?

    4. according to a book i read, NH3 cannot act as oxidising agent because N is already in its lowest ox state. but, why cant we consider Hydrogen's effect?
    for example,
    NH3+ 3Cl2 --> NCl3 + 3HCl
    in this, N in NCl3 attracts the bonded pair more because of its small size. so, Cl should have a positive ox state (+1). why is this not considered? and if it is, how is the thing explained in this reaction?

    Thanks in advance :)
     
  2. Trippy ALEA IACTA EST Moderator

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    10,361
    Yes, it's part of they're (part of) the reason for the observed trends on the periodic table along the rows.

    They may not participate in bonding directly, however, they do have a role to play in shielding the valence electrons from the nucleus

    What inert pair effect? ;)

    Have you learned about the shapes of orbitals yet? Or are you still dealing with the octet rule?

    You may have to rephrase this a little - if you're asking what I think you're asking, it looks like you're asking if Zuchinni and Courgette are different.

    NH[sub]3[/sub] = N[-III] + 3*H[+I]
    Cl[sub]2[/sub] = 2*Cl[0]
    NCl[sub]3[/sub] = N[+III] + 3*Cl[-I]
    HCl = H[+I] + Cl[-I]
     
  3. arauca Banned Banned

    Messages:
    4,568
    3 bond energy means the energy that is holding the two atons together
    the dissociation energy have to be higher you are breaking the bond

    4 look onto electronegativity table you see chlorine os 3.16 and nitrogen 3.04 so chlorine retains its electron stronger then nitrogen
    In the case of ammonia you can say nitrogen oxidized Hydrogen and so nitrogen acquired the octet and in essence the hydrogen become acidic , but ammonia is a base because nitrogen it have additional pair of unshared electrons site and that site is negatively charged and so it accepts a proton to make NH4 which is acidic .
     
  4. rohIT Registered Senior Member

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    76
    thank you arauca and Trippy:)
    in the book i was referring, both N and Cl had en 3 and i thought N would pull the electrons more due to small size! thanks for the en values :)
    @ Trippy
    Inert pair effect is the reluctance of s orbital electrons to participate in bonding (if i understood it right!). it increases down the group, due to which Bi has +3 oxidation state more stable than +5. i did not understand WHY it happens though.
     
  5. arauca Banned Banned

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    4,568

    I don't know if you want the answer from Trippy or any one ?
     
  6. rohIT Registered Senior Member

    Messages:
    76
    i mentioned Trippy in the reply cause i was asked "What inert pair effect? "
    i need an answer. a correct answer from any source is welcome :)

    and, there is a new "twist" in this NCi3 story...
    NCl3 + 3 H2O --> NH3 + 3HOCl
    and, this suggests a -3 oxidation state for N. can you please explain if this is still compatible with Cl being more electro negative? and, if it is, please tell me how :)
    thanks!
     
  7. Trippy ALEA IACTA EST Moderator

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    10,361
    In this reaction, the oxidation number of Nitrogen changes from +III to -III.
    But this isn't the only change.

    The oxidation number of Oxygen also changes from -II to 0.

    Yes. This is compatible with Cl being more electronegative than N.

    In the first instance, what we have is this: [sup]δ+[/sup]N-Cl[sup]δ-[/sup]
    In the second instance, we have this: [sup]δ-[/sup]N-H[sup]δ+[/sup]
    So the bonding electrons of the N-H bond in spend more time near the N, but the bonding electrons in the N-Cl bond spend more time near the Cl.

    Think of it as a continuum between covalent bonding and Ionic bonding, if that helps.
     
  8. rohIT Registered Senior Member

    Messages:
    76
    H2O splits into H+ and OH-
    when you say Nitrogen's Ox. state changes from +3 to -3, i am unable to understand from where the electrons come.
    And, Oxygen's oxidation state in the product remains -2 as en of O (3.44) is greater than en of Cl (3.16).
    Moreover, if Cl- is released, how can it combine with OH- (they must repel each other..)
    please explain in more detail or give me a link where i can read about it in detail :)
    thanks!
     
  9. arauca Banned Banned

    Messages:
    4,568

    In an hydrolysis NCl3 in an alkaline media, liberated heat
    2 NCl3 + 3 NaOH + n H2O----> 2NH3 | + 3 Cl2 + 3NaOH ----> 3NaCl + 3HOCl
    So in this steps Cl is converted from Cl -1 to Cl a + 1l
    since this is an aqueous system Nitrogen retains the electron from expelling the Chlorine and converting it to salt NaCl .
    Nitrogen gets its Hydrogen from water and because alkalinity it us expelled as ammonia
    Note : NCl3 is an unstable liquid explode ate its boiling point
     
  10. rohIT Registered Senior Member

    Messages:
    76
    hello :) and thanks for showing interest in answering my question. i almost lost hope of finding a satisfactory answer.

    and, i am still at a loss at understanding why chloride ions, which you said are formed, lose their electrons. i guess if i understand this, i will get my answer :)

    thanks you once again :)
     
  11. arauca Banned Banned

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    4,568
    Perhaps the beginning misunderstanding was of the NCl3 which is covalent , as when you add water Ammonia and chlorine gas are formed , then Chlorine gas react wit water you form HOCl and HCl
    as you know chlorine gas is covalent , when it split one atom becomes Cl- and the other Cl+ ,
    I thing the problem started before they suspended me , and I pointed out the that NCl3 is covalent , and he, from his embarrassment suspended me.
     
  12. Trippy ALEA IACTA EST Moderator

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    No - don't forget about chlorine radicals.

    The fact that NCl[sub]3[/sub] is covalent had nothing to do with it. The use of oxidation numbers is not restricted to covalent compounds. I knew NCl[sub]3[/sub] was a covalent compound before you posted.

    I will, however, concede that I got the wrong Oxidation state for Oxygen in Post #7 in the hypochlorite anion, it should have been (-II) not (0). But then, that's not what you objected to, and it's not an objection you have raised*.

    You were banned for trolling and meaningless post content. Keep it up, and it will happen again.

    *Addendum:
    It seems I may also have erred in the oxidation state of Nitrogen in Nitrogen trichloride. It seems that its reactivity is better accounted for if you treat it as N(-III) and Cl(+I), which still isn't the objection you raised. In fact you make the same mistake I did in Post #9 in assigning Cl a -1 oxidation state.
     
    Last edited: Apr 25, 2012
  13. arauca Banned Banned

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    4,568
    How can it be N with an electronegative lover then Cl , you still have not learned N(-III) and Cl(+I) ( I suppose you have a special electronegative table.
     
  14. Trippy ALEA IACTA EST Moderator

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    A reference for what, precisely? To prove that Oxidation numbers can be applied to covalent compounds?
    To prove that in some cases reactions of elemental chlorine proceed by homolytic bond cleavage rather than heterolytic bond cleavage?

    You're mistaken. Pointing out that although I was wrong, it wasn't for the reasons you suggested is not making excuses, and it is admitting my error.

    Consider this your final, official warning. Keep up the insults and you will be banned (again).

    This makes little, if any sense. It's not at all clear what you're objecting to, or what you think I haven't learned. Are you saying tht I am wrong in suggesting that the oxidation numbers are N(-III) and Cl(+1)?
    Because according to the published literature, the electronegativities are similar enough that other effects can predominate. the reaction proceeds by nucleophilic attack of the chlorine. In this case, it boils down to the fact that the Chlorine is bigger than the nitrogen, and able to easier expand its electron shell to accomodate extra electrons.

    If you want to understand what difference this makes, compare the hydrolysis of nitrogen trichloride with the hydrolysis of nitrogen trifluoride.
     
  15. arauca Banned Banned

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    4,568
    Do me a favor stop threatening me. You are not paying me salary. there are other forums .


    This makes little, if any sense. It's not at all clear what you're objecting to, or what you think I haven't learned. Are you saying tht I am wrong in suggesting that the oxidation numbers are N(-III) and Cl(+1)?
    Because according to the published literature, the electronegativities are similar enough that other effects can predominate. the reaction proceeds by nucleophilic attack of the chlorine. In this case, it boils down to the fact that the Chlorine is bigger than the nitrogen, and able to easier expand its electron shell to accomodate extra electrons.

    If you want to understand what difference this makes, compare the hydrolysis of nitrogen trichloride with the hydrolysis of nitrogen trifluoride.[/QUOTE]

    You might not like but to tell you NF3 dies not hydrolyze.
     
  16. Trippy ALEA IACTA EST Moderator

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    10,361
    Stop being rude, and I won't have to threaten you. See how it works?


    Actually, yes it does: Hydrolysis of the Nitrogen Fluorides; Hurst & Khayat.

    It just requires basic conditions and high temperature. Hurst and Khayat conducted their experiments at 100°C (that's 212°F for the americans reading this). By comparison, the nitrogen trifluoride was still recoverable after one week of contact with excess dilute acid or pure water at 133°C (271°F).

    They hydrolyzed it, and got nitrite and fluoride as their products.

    I notice that you haven't answered any of the questions I asked you directly in my previous post.
     
  17. arauca Banned Banned

    Messages:
    4,568

    It seems that its reactivity is better accounted for if you treat it as N(-III) and Cl(+I), which still isn't the objection you raised.

    I don't have any objection that nitrogen can be positive or negative , and so does chlorine . I don't have any objection that chlorine starts as a free radical, then it can acquire an electron or lose one , then it becomes a ion,and will hold the electron and will not hold it and will not share it. Now Of the other atom will not release its electron and they have high affinity for the electron they will share the electron with the incoming atom, In case of Florine or oxygen they have a high affinity and so they will polarize the molecule , but the 2 free electrons in the nitrogen atom will be distorted to give stability to the molecule
    I don;t know if this answers your question.
     

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