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When drawing Lewis structures, are you supposed to always draw the different resonance structures and find the formal charges? For example, for 2B. 11C, when drawing H2C(NH2)COOH, if my structure is different from the solution structure, would it be wrong? Or would I have to find the formal charges of the atoms for my structure and keep drawing different structures to match the solution?
I don't think it would necessarily be considered wrong, but having a lower formal charge means greater stability, so drawing the Lewis Structure accordingly would be the best answer. Probably if the test specifically asks for the Lewis Structure with the lowest formal charge, then drawing out each one with different resonance might be necessary.
I agree with the above response, that most of the time you want to draw the one with the lowest formal charge. One kind of short-cut that I've noticed from doing problems that helps me is that when Oxygen has two covalent bonds and 4 lone pairs, it formal charge is zero and when carbon has four covalent bonds, its formal charge is zero -- so when I'm making my first attempt at a lewis structures, I try to roughly stick to these short cuts to keep the formal charges relatively low.
You only have to include additional resonance structures if it asks you to (One of the UA's said this today in a review session). As far as the formal charge goes, I think you should include it just to be safe, but I'm not sure if its always needed. It will help you to determine if your structure is correct though
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