Question 4.11: Drawing Resonance Structures The nitrate ion, NO3^-, has thr......
Drawing Resonance Structures
The nitrate ion, NO_3^-, has three equivalent oxygen atoms, and its electronic structure is a resonance hybrid of three electron-dot structures. Draw them.
STRATEGY
Begin as you would for drawing any electron-dot structure. There are 24 valence electrons in the nitrate ion: 5 from nitrogen, 6 from each of 3 oxygens, and 1 for the negative charge. The three equivalent oxygens are all bonded to nitrogen, the less electronegative central atom:
\begin{matrix} \quad\underset{|}{O} \\ \quad \underset{\diagup\quad \diagdown }N \end{matrix} \\ O \qquad \quad O 6 of 24 valence electrons assigned
Distributing the remaining 18 valence electrons among the three terminal oxygen atoms completes the octet of each oxygen but leaves nitrogen with only 6 electrons.
\left[\begin{matrix} \quad:\underset{|}{\overset{..}O}: \\ \quad \underset{\diagup\quad \diagdown }N \\ \quad :\overset{..}{\underset{..}O} \qquad \quad \overset{..}{\underset{..}O}: \end{matrix}\right]^-To give nitrogen an octet, a lone pair must move from one of the oxygen atoms to become part of an N-O double bond. But which one? There are three possibilities, and thus three electron-dot structures for the nitrate ion, which differ only in the placement of lone-pair and bonding electrons. The connections between atoms are the same in all three structures, and the atoms have the same positions in all structures
