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Homework Help: Hey, I'm new here and need some help

  1. Jun 19, 2007 #1
    Hey, I'm new here and need some help with Dot Structure homework.

    Hey everyone, I was looking for help in the net, I saw the forums and felt like joining in for some help.
    I got some homework our Chemistry teacher gave us today, but I'm kind of lost in here as I am not goo in chemistry...Here is what i need help with if someone could spare me a minute:

    Problem Number 1 asks me to draw as many resonance structures as I can for HN3.
    I'll have something like this if i break it down: H-N-N-N but here on I'm all lost!

    Problem Number 2 asks me to draw electron dot structure (wich I still don't really understand...) for each molecule and I have to explain why it falis to obey octet rule. Molecules are a. BeF2, b. SiF6, c. ClO2, d. BF3, e. XeF2.

    If someone could help me understanding the problems, I would appreciate it so much. Our chemistry teacher is kind of crazy, and starts going off topic every time he teaches us.

    Last edited: Jun 19, 2007
  2. jcsd
  3. Jun 19, 2007 #2
    i kno that kinda of teacher... i'll b able to help you only on the dot and cross diagrams.

    : represents a shared pair of electron, one from each atom.



    there are only 4 e- around the Be atom, instead of 8... that's why it does not obey the octet rule....
    F F
    .. ..
    .. ..
    F F

    i guess it should have been [SiF6]2-. coz, 4 of the F atoms share an e- with Si, but the 2 others are fluoride ions, i.e. F-. Si has only 4 e- to share, and it accepts two e- from each F- ion since it has vacant and accessible 3d orbitals....
    it fails to obey octet rule as it has 12 e- around it...

    .. . ..
    .. .. ..
    here, both shared pairs are provided by the Cl atom.... resultingly, the Cl atom has one unpaired elcetron...


    B shares 3 e- withh the F atoms.... but it has only 6 e- around it, hence does not obey octet rule

    i kno ot's really confusing, bt i couldn;t make it better....
  4. Jun 19, 2007 #3
    Wow thanks, i was not expecting an explanation actually, more like a post saying "get out of here, you 00b!" so thanks a lot.
    Now, Im still trying to figure out how you get to know how many e- an element has around?
  5. Jun 21, 2007 #4
    aaww.... i'll try to explain..... the periodic table helps you a lot....
    in the diagrams above, i was considering only the outermost orbital(or quantum level).... the inner ones usually do not take part in bonding.....

    i don't really kno about the octet rule, bt i think i've figured it out...
    so atoms obeying the octet rule will definitely have 8 e- in their outermost orbital. you just have to count the electrons in the inner orbitals then....
  6. Jun 21, 2007 #5


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    Firstly, welcome to PF Thorzilla. I should point out the PF Guidelines which state that full solutions should never be given, and that help can only be given when the original poster shows some work. There are two reasons for this; firstly, so we don't do your homework for you, but secondly so we can gauge the level of the student's knowledge and so don't aim the answer either too high or too low.

    Perhaps this link may help: http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/perlewis.html

    The octet rule states that atoms tend to combine so that each atom has 8 electrons in its outer shell-- i.e. it has the stable electron configuration of an inert gas.
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