As mjc123 states, your initial guess is incorrect because nitrogen cannot have 5 bonds.
Nitrogen is a period-2 element and so
always follows the octet rule. It will never have more than 4 pairs of valence electrons.
Period-3 elements like P and S and Cl are sometimes observed breaking the octet rule, e.g. PCl
5. This is because of the phenomenon of an expanded octet. Basically, the energy level of the 3
d orbitals is low enough that they can participate in bonding. You can start learning more about it
here.
You might wonder why nitrate doesn't have the following form:
This is because the nitrate ion is a classic example of resonance. There is a lone pair of electrons that kind of "float around" the molecule (they're delocalized), creating bonds that are not quite single and not quite double bonds between the N and all the O.
Because of all of this, we get the structure for [itex]\ce{NO3-}[/itex]