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The lewis structure where the formal charges of the atoms are close to zero result in lower energy/more stable structures, so these are the best structures based on formal charge. To determine which resonance structure is the best on formal charge, you want to choose the structure that has the least amount of formal charges and formal charges that are closest to zero.
The best way to choose the most stable resonance structure is to choose the structure that has allows the most amount of atoms to have a formal charge of 0. It is also preferable if the central atom has a formal charge of zero. If many atoms have formal charges of -1 or +1 then it is not an ideal structure. 0 provides the most stability and the lowest energy state and as a result is often the most common form when found in naturally.
To find the best resonant structure, one has to find the formal charge for each atom, and add the absolute values of each of them to see which sum is closest to 0. Then look for symmetry in the bonds and oxidation states to see which lewis structure overall best represents the actual structure.
In question five didn't it say that the extra electrons associated with the model should be given to the atom with the greater electronegativity? Yet Cl is more electronegative than O and it's also at the center. Could someone explain when to apply one principle and when to apply the other?
Also if two resonance structures exist for which one has only one formal charge but it's located on the central atom and the other has two formal charges but they're located on the outlying atoms which one is more preferable? Does limiting the number of formal charges take precedence or keeping formal charges off of the central atom?
In order to find the formal charge, you look at each atom within the molecule and find its formal charge. The resonance structure with the lowest amount of charges and changes will be the best one
I also found this idea questionable. I had a very hard time. However, the best way to think of it is we are trying to minimize the formal charge to create a neutral atom. So, with resonance, the best way to get the best answer is by having the lowest formal charge more neutral more stable more likely to be in this state.
From what I read, the formal charges of the individual atoms is important to determining which model is the most plausible. In the answers that were correct, they had only one atom that had a non-zero formal charge. For example one model had a Cl(-1) and another had O(-1), with the rest of the atoms in the molecule having a neutral formal charge.
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