# Out of NO+, NO2-, NO3- which has the longest NO bond and which has the shortest NO bond?

##### 1 Answer

The differences here include the number of oxygens attached to nitrogen. Notice the bonding patterns:

Based on the

Based on the

If you pay attention to the way the oxygens always balance out to give a final charge, notice the following observations:

#"NO"^(+)# , with only one oxygen, has a formal charge of#+1# on oxygen and#0# on nitrogen.#"NO"_2^(-)# , with two oxygens, since there is a#0# formal charge on nitrogen, then the oxygens each share a#-"1/2"# charge (#-1/2xx2 = -1# charge overall).#"NO"_3^(-)# , with three oxygens, since there is a#+1# formal charge on nitrogen, the remaining charge gets distributed onto all three oxygens, balancing out to be#-"2/3"# per oxygen (#-2/3xx3 + 1 = -1# charge overall)

*This is interesting, because the oxygens spread out the electron density more and more towards them as the number of oxygens increases.*

This spreading out decreases the average electron density within each **bond order**, as shown below.

When you take the **best** resonance structure (not the hybrid structure, but the typical resonance structures you draw), you can count one electron per bond to do the following calculations:

- The bond order for
#"NO"^(+)# is#"3 electrons"/"1 bonding group" = 3# . - The bond order for
#"NO"_2^(-)# is#"3 electrons"/"2 bonding groups" = "3/2" = 1.5# . - The bond order for
#"NO"_3^(-)# is#"4 electrons"/"3 bonding groups" = "4/3" ~~ 1.33# .

So, you can see the **bond order decreases** as the number of oxygens in these **increases**.

The **higher** the bond order, the **stronger** the bond and thus the **shorter** the bond.

Therefore,