Answer
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Work Step by Step
The three N-O bonds in the nitrate ion ($NO_{3}^{-}$) are all equivalent in length and strength, even though the valid Lewis structure for $NO_{3}^{-}$ has one double bond and two single bonds to nitrogen.
This can be explained by the concept of resonance in the nitrate ion.
The correct Lewis structure for $NO_{3}^{-}$ shows one double bond and two single bonds to nitrogen:
```
O
//
N-O
|
O-
```
However, this is not the only valid Lewis structure for the nitrate ion. There are two other equivalent resonance structures that can be drawn:
```
O-
//
N-O
|
O
```
```
O
|
N-O
|
O-
```
These three resonance structures contribute equally to the overall structure of the nitrate ion. As a result, the three N-O bonds are equivalent in length and strength, even though the individual Lewis structures show different bond types.
The resonance stabilizes the nitrate ion and delocalizes the negative charge, making all three N-O bonds equivalent. This is a common phenomenon observed in many polyatomic ions and molecules with delocalized π-systems.
