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Homework Help: Chemistry Grade 12 Help|

  1. Nov 7, 2005 #1
    Chemistry Grade 12 Help|URGENT

    Hi, I need some help with this question.

    1)Phosphorus forms PCl3 and PCl5. Nitrogen forms NCl3 but not NCl5. Explain the reason why NCl5 doesn't form?
    I know Phosphorus & Nitrogen are an exceptional to the octet rule but I don't know why NCl5 doesn't form.

    2) If N, C and O all form sp3 hybrid orbitals, what reason can you give for NH3 and H2O being polar while CH4 is not.
    I don't even know where to start. please help.

    If you need me to rephase the question, please comment.
    Also, a link to a site which could help me would be more than helpful.
    Last edited: Nov 7, 2005
  2. jcsd
  3. Nov 7, 2005 #2
    1) think about the size of the phosphorus atom compared to that of nitrogen
    2) draw the lewis structures first
  4. Nov 7, 2005 #3
    This is what I wrote in my assignment:

    1.Phosphorus forms PCl3 and PCl5. Nitrogen forms NCl3 but not NCl5. To tell you the reason why that is, I have to define what a non-conformist means. The definition a non-conformist is when an atom that does not follow the octet rule. Phosphorus and Nitrogen both are non-conformist. Phosphorus, however, is an atom that has more then 4 bonding and Nitrogen is an atom that contains an odd number of electrons. NCl5 would have 40 electrons which is an even number.

    2.If nitrogen, oxygen and carbon all from sp3 hybrid orbitals, NH3 and H2O being polar while CH4 is not. The reason why ammonia and water are polar is because they have uneven distribution of electron density while methane is evenly distributed of electron density. CH4 have the same forces being pulled all four ways while NH3 and H20 don't.Water is polar because of the 2 lone pairs. Theoretically, if there was H40, it would be a non-polar. Again, if there was NH4, it would be non-polar too.

    Is this correct?
    Last edited: Nov 7, 2005
  5. Nov 7, 2005 #4
    The answer to (2) would rely on you explaining WHY H2O is a 'bent' shape and CH4 isnt.
  6. Nov 7, 2005 #5
    I just edited the answer for question 2 on my previous post.

    Another question that I am having trouble with:
    What is the relation between the angles of clouds in a molecules and the orbital configuration?

    I need the answer for this to answer this question:
    The bond angles in CH4, NH3 and H2O are 109.50, 1070 and 104.50 respectively. How can these values be justified if sp3 hybrid orbitals are invloved in each case?
  7. Nov 7, 2005 #6
    There is NH4, its called ammonium..
    The bond angles of molecules depend solely on the combination of electron domains and molecular bonds. The E.D. tells you what the geometric shape of the bonds will be, then when you draw out your bonds and take off your empty electron domains youll get the molecular shape.
    Last edited: Nov 7, 2005
  8. Nov 7, 2005 #7
    You haven't really said anything here except that they both violate the octect rule. NCl5 doesn't exist because nitrogen is too small to have 5 chlorine atoms "fit" around it.
  9. Nov 11, 2005 #8
    Atoms which violate the octet rule such as phosphorus or sulfer are capable for sp^3d or sp^3d^2 hybridization accouting for the greater number of availible bonds. This doesn't occur with nitrogen because it doesn't have a d orbital to fill with electrons during hybridization. Hope that makes sense, but I'm sure you've already figured it out.
  10. Nov 13, 2005 #9
    Yea, I figured it out. My friend told me that nitrogen doesn't have enough orbitals to get 5 ionic clouds like phosphorus.
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