Resonance in  Nitrate Ion

In figure 1.1 we see three resonance structures of nitrate ion.

Figure 1.1: Three resonance structures of nitrate ion. Note, for ions, we place the Lewis dot structure in brackets and the charge as a superscript on the outside of the bracket. In section 1.1 we will learn how to draw Lewis dot structures, but it needs to be noted that you have extra electrons for anions, and fewer for cations.
If we were to merge the Lewis dot structure into one figure like we did in fig. 8.3.4 for ozone

Figure 1.2. In this figure we have mixed the three resonance structures in figure 1.1 into one structure, where the multiple bond (line plus dashed line) represents one double and 2 single bonds, and so has a bond order of 1.333.

It is important to note that the dashed lines in figure 8.3.4 and 1.2 have different meanings, and so the dashed line itself does not indicate the magnitude of the multiple bond, just that it is bigger than a single bond and smaller than a double.