Resonance Structure1 - molecule. In these cases it can be...

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Resonance Structures 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 
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Unformatted text preview: molecule. In these cases it can be helpful to know which structure has the greatest contribution to the final structure. If you have many possible resonance forms, you choose the most likely resonance form by calculating the formal charge on each atom in each resonance form. In these situations it is helpful to calculate the formal charge on each atom in each possible resonance structure, and use the formal charges to determine the most representative structure. Formal charge = Group number - number of nonbonding e-- (number of bonding e-) / 2. In the example below, we calculate the formal charge on each atom in a Lewis structure. What are the formal charges on each atom in NO 2-? The sum of the formal charges must equal that of the compund or ion. So, 0 + 0 - 1 = -1 as expected for NO 2-....
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Resonance Structure1 - molecule. In these cases it can be...

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