After reading the description of your problem, I think that you
have miscalculated the number of valence electrons in the compound. I'll
break it down here. H = 1 e- N = 5 e- 3 X O(6) = 18
Total valence electrons = 24
The structure of nitric acid is sort of deceiving, but is explained on
pages 10 & 12 of the textbook. I think that this structure is
an exception to the rule. This structure threw me at first because of
its formal charge. With only one N=O double bond, one oxygen has a formal
charge of -1. I then realized that this was counteracted because the
nitrogen only has 4 bonding pairs. 5 valence electrons - 4 bonding pairs
= +1 formal charge. Therefore the molecular formal charge is O,
essential for an electrically neutral compound. I hope that this has
been helpful.
Andy Glandon