H2 chemistry N2O oxidation number question

• poobyboop

  28 Jun 13, 13:04

  Hi wondering if anyone can help with this question:

  using this structure of N2O,

  

  looking at just the one on the left, (more likely one i suppose), whats the proper way to calculate the oxidation number for each of the atoms?

  and will the average O.N. of the 2 Nitrogen atoms give +1 (e.g. first N is 0 while second N is +2) which is nitrogen's oxidation state in N2O or do both nitrogen atoms(in this case) have to have an oxidation number of +1?

• UltimaOnline

  28 Jun 13, 14:20

  Using my BedokFunland JC formula for Oxidation State (OS) aka Oxidation Number (ON), we have :

  Oxidation State = Formal Charge + Electronegativity Consideration.

  There are 2 resonance contributors and 1 resonance hybrid.

  Considering the N=N=O resonance contributor, the terminal N atom has
  Oxidation State = Formal Charge + Electronegativity Consideration = (-1) + (0) = -1

  Considering the N=N=O resonance contributor, the central N atom has
  Oxidation State = Formal Charge + Electronegativity Consideration = (+1) + (+2) = +3

  Hence average OS of N in this resonance contributor = ((-1) + (+3)) / 2 = +1

  Considering the N(triple bond)N-O resonance contributor, the terminal N atom has
  Oxidation State = Formal Charge + Electronegativity Consideration = (0) + (0) = 0

  Considering the N(triple bond)N-O resonance contributor, the central N atom has
  Oxidation State = Formal Charge + Electronegativity Consideration = (+1) + (+1) = +2

  Hence average OS of N in this resonance contributor = ((0) + (+2)) / 2 = +1

  Since O is more electronegative than N, the N(triple bond)N-O resonance contributor is  more significant compared to the N=N=O resonance contributor, thus in the resonance hybrid (ie. the actual molecule), the OS of the terminal N atom is in between, but slightly closer to 0 than -1; and the OS of the central N atom is in between, but slightly closer to +2 than +3.

   

  Originally posted by poobyboop:

  Hi wondering if anyone can help with this question:

  using this structure of N2O,

  

  looking at just the one on the left, (more likely one i suppose), whats the proper way to calculate the oxidation number for each of the atoms?

  and will the average O.N. of the 2 Nitrogen atoms give +1 (e.g. first N is 0 while second N is +2) which is nitrogen's oxidation state in N2O or do both nitrogen atoms(in this case) have to have an oxidation number of +1?

   

• poobyboop

  28 Jun 13, 15:00

  Great thank you!

  And just to clarify, the O.S of N calculated using the 'typical' way

  (i.e. 2N + (-2) = 0  ==> N=+1)

  will be the same as the average OS of N using the formula of you stated, and this is true for other covalent molecules too right?

• UltimaOnline

  28 Jun 13, 15:22

  Originally posted by poobyboop:

  Great thank you!

  And just to clarify, the O.S of N calculated using the 'typical' way

  (i.e. 2N + (-2) = 0  ==> N=+1)

  will be the same as the average OS of N using the formula of you stated, and this is true for other covalent molecules too right?

  
  Yes, that's right. But that method (what I call the 'O' level method) is not reliable, and may fail under various unusual circumstances (eg. tetrathionate ion, due to the peroxo group). But for normal 'A' level purposes, it's still ok.