breaking octet rules with electronegativity

[Kellylin_4D]

How come in some bondings, such as CN minus, you put the extra electron with the C, even though the N is more electronegative, just because the N fulfilled the octet rule already, but in N2O, it is better to make O the negative charge, rather than the N? How do I know? And don't Oxygen prefer double bonds as well so that if the negative is with N, then oxygen get's to be neutral, and double bonded? Thank you!

[Sahil Jog 1F]

The reason why you may put the extra electron on one atom and not the other does not depend on electronegativity, but depends on the formal charge. Since it is a universal rule that most things in the universe love to attain maximum stability, the most stable Lewis Structure of a molecule would be the one with the most stable formal charges, and thus looking at the formal charges let's you figure out why certain molecular structures of molecules exist over others. In the case of N2O, it would be the most stable with nitrogen triple bonded to another and single bonded to the oxygen.

[Sahil Jog 1F]

Correction on the last part of my response: N2O would be most stable when triple bonded to a nitrogen and double bonded to the oxygen*