Question

What is the lewis dot structure of nitrate ion?

I have seen everyone draw the lewis dot structure of nitrate ion, putting 7 electrons around the oxygen atoms, while only 6 are supposed to be there. I see everyone doing the same thing. Please kindly explain.

Answer 1

Well we got nitrate ion...and this gives `5_N+3xx6_O+1_"negative charge"=24*"valence electrons"` with which to play....

Explanation:

The nitrogen centre is quaternized, i.e. it formally bears a positive charge...because in the following resonance structures there are SIX ELECTRONS associated with it rather than the SEVEN electrons required for neutrality (we can count out the 4 valence electrons; there are 2 inner core electrons)....

And thus for `O=stackrel(+)N(-O^(-))_2`, 3 of the 4 participating atoms bear a formal charge. The nitrogen, that has FOUR valence electrons, rather than the five required for neutrality, thus has a FORMAL positive charge in each of the mesomers. And given one mesomer, TWO of the oxygen atoms bear 7 electrons, i.e. three oxygen-based lone pairs, and one electron from the `N-O` bond to give the 7 electron tally, and a formal anion. The doubly bound oxygen has 6 valence electrons, and is formally neutral.

For the parent nitric acid we would likewise write....

`H-O-stackrel(+)N(=O)(-O^(-))`, a neutral molecule, but still with formal charge separation.....