One possible Lewis representation of the nitrate ion, NO3⁻, is shown below (lone pairs omitted for clarity):
O═N–O⁻ with the third oxygen singly bonded to nitrogen. All atoms have complete octets.
(a) Draw all additional valid Lewis resonance structures for the nitrate ion, showing formal charges and lone pairs.
(b) For the resonance structure given in the stimulus, determine the total number of σ bonds and the total number of π bonds.
(c) Using the complete set of resonance structures from part (a), calculate the average (resonance) bond order for the N–O bonds. Explain how this bond order correlates with observed N–O bond lengths relative to typical N–O single and double bonds.
(d) Identify the most likely hybridization of the nitrogen atom and of an oxygen atom that is formally single-bonded to nitrogen in one resonance contributor. Justify each assignment using both electron-domain geometry and bonding considerations.