Hello! I was drawing the lewis structure for NO3- and was wondering why O=N-O-O- isn't a 'valid' predicted structure (Double-bonded O to nitrogen, a single-bonded oxygen to nitrogen, a lone pair on nitrogen, and a single-bonded oxygen to oxygen with a negative charge on the terminal oxygen. For the nitrate ion its N with three oxygens attached, with a + charge on the nitrogen and two oxygens with negative charges. Explanations for the nitrate ion start with "Nitrogen is the central atom", and the structure then follows; why assume this, particularly in more general cases? If it isn't assumed, then why can't you arrive at the structure I gave first of all? Any help appreciated, Nobahar.