Question

Using the Lewis electron dot structure for `NO_3^-`, what is the total number of non-shared electrons?

Answer 1

Given the ONE resonance isomer, there are 8 (unshared) lone pairs on the oxygen atoms.

Explanation:

`(O=)N^(+)(-O)_2^(-)` is the typical resonance isomer. Such a structure demands that the doubly bound oxygen has 2 lone pairs, and each of the singly bound oxygen have 3 lone pairs.

Because there are 7 valence electrons around each singly bound oxygen atom, these atoms have a formal negative charge. To balance this `-2` charge, the quaternized nitrogen, which has 4 valence electrons, has a formal `+1` charge. This is entirely consistent with the ionic charge of the nitrate ion. Why?