Question 8.3.2: a. What is the bond order of the nitrogen–oxygen bonds in th......
a. What is the bond order of the nitrogen–oxygen bonds in the nitrate (NO_{3}^{−}) ion?
b. In which ion (NO_{2}^{−} or NO_{3}^{−}) are the nitrogen–oxygen bonds longer?
c. In which ion (NO_{2}^{−} or NO_{3}^{−}) are the nitrogen–oxygen bonds stronger?
You are asked to identify the bond order in a molecule or ion that has resonance structures and to use bond order to make predictions about relative bond length or bond order in a series of molecules or ions that have resonance structures.
You are given the chemical formula of a molecule or ion, or a series of molecules or ions.
a. The nitrate ion has three equivalent resonance structures.
There are four NO bonding pairs distributed over three NO bonding locations.
each NO bond order in NO_{3}^{-}=\frac{\text{total number of NO bonding pairs}}{\text{number of NO bond locations}} =\frac{4}{3}=1.3
b. Bond length increases with decreasing bond order. The nitrogen–oxygen bond order in NO_{3}^{-} is less than the nitrogen–oxygen bond order in NO_{2}^{-} (1.3 versus 1.5, respectively). Therefore, NO_{3}^{-} has longer nitrogen–oxygen bonds than does NO_{2}^{-}.
c. Bond energy increases with increasing bond order. The nitrogen–oxygen bond order in NO_{2}^{-} is greater than the nitrogen–oxygen bond order in NO_{3}^{-} (1.5 versus 1.3, respectively). Therefore, NO_{2}^{-} has stronger nitrogen–oxygen bonds than does NO_{3}^{-}.