How to draw NO2 correctly?

• limywv

  16 Nov 09, 17:20

   

   

   

  
  
• TrueHeart

  16 Nov 09, 17:34

  Originally posted by limywv:

  Guys, this question has been a major bugbear for me for quite some time now...I've searched the internet but no dot-and-cross diagrams were offered...can anyone help me on this?

   

  thanks

  Hi limywv,

  Do have a look at this:

  http://www.docbrown.info/page06/molecule_shapes2.htm

  Cheers.

• UltimaOnline

  16 Nov 09, 17:50

  A couple years ago, my student was just about the only one in her cohort who could correctly draw the structure of NO2 in a major exam. My point is (not about boasting, but about) most JC teachers don't focus (not blaming them though, they have it tough enough) on teaching the relevant, fundamental and crucial aspects of Chemistry that empower students to understand, appreciate and enjoy the Science as an Art. JC students most often fail to allow themselves to do the above (not blaming them though, they have it tough enough), and instead blindly memorize their way through JC. Specifically (for this question), I refer to the concept of formal charges and resonance (that is ill-taught in JCs), without an understand of these, drawing structures become senseless and hopeless. To answer your question : Central atom is N (with a +ve charge), single (and dative) bonded to an O atom (with a -ve charge), and double bonded to a (neutral) O atom. The N atom thus has 3 bond pairs and an unpaired electron, the (-ve charged) O atom has 3 lone pairs and 1 bond pair, the (neutral) O atom has 2 lone pairs and 2 bond pairs. The electron geometry is trigonal planar, the molecular geometry is v-shape or bent or non-linear. The resonance hybrid sees each of both N to O bonds as having bond lengths & bond strengths equivalent to 1.5 bonds. The charge on each O atom is an averaged -1/2 charge. For 'A' levels exams, it will suffice to draw a single resonance contributor.
• limywv

  16 Nov 09, 18:15

   

   

   

  
  
• UltimaOnline

  16 Nov 09, 19:13

  Yes, that’s correct on both counts (N atom has 7 electrons in terms of an octet, and 4 electrons in terms of formal charge). If the question tasks you to draw NO2, it might also require you to draw N2O4 in the same qn. The unpaired electron in one NO2 molecule combines with another unpaired electron in another NO2 molecule to form N2O4.
• limywv

  16 Nov 09, 23:29