Part B. Consider the four resonance structures of the phosphate ion:
Calculate the average formal charge on a single oxygen atom, such as the one shown in blue, as it appears on all resonance structures, A to D.
Express your answer numerically as a decimal or fraction.
For example, consider the two Lewis structures for the sulfate ion (SO42−):
In the normal octet structure, sulfur has a +2 formal charge and all four oxygen atoms have a − 1 formal charge. Because sulfur belongs to the third period, it shows an expanded octet that minimizes the formal charge on each of the atoms. Thus in the expanded Lewis structure for a sulfate ion, the sulfur atom has 12 valence electrons, and the formal charge on the sulfur atom gets reduced to 0 by forming two sulfur-oxygen double bonds. The formal charge on two oxygen atoms also gets reduced to 0.
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