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Unformatted text preview: The Lewis structure for certain molecules or ions can be drawn in more than one way. For example, for NO 2- the number of valence eletrons is 5 + 2 (6) + 1 = 18 e- (or 9 pairs), and we find that there are two equally valid Lewis structures that can be drawn: Which one is correct? Well, you would expect that the doubly bonded oxygen-nitrogen distance to be slightly less than the singly bonded distance. Actually, what is found experimentally is that both N-O distances are equivalent. The true structure of the molecule is a combination of the two. Anytime you have more than one valid structure for a molecule or ion, you have what are known as resonance structures. So in this case, both resonances structures contribute equally to the final structure of the molecule. Sometimes you will have multiple resonance structures which do not contribute equally to the final structure of the molecule. In these cases it can resonance structures which do not contribute equally to the final structure of the molecule....
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