I am stuck on this exercise problem from the book "Chemistry³":
http://www.image-share.com/upload/3878/273.jpg
How do I know that this is the correct electron arrangement?
It seems to me like I can share the electrons in an almost infinite number of ways, like create a pair between the left NN-bond and then take two electrons from the oxygen atom to the right and then take whatever that's necessary to get as close to the octet rule etc;
why is the arrangement in the solution for this problem the correct answer?
Am I really just supposed to "guess" until I find charges that are as low as possible on all atoms, or is there some cleaner and more reliable way to do this?
("Equation 5.1" is just the definition for Formal Charge)