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Solution:  For the molecule BF3, if we write the Lewis dot structure b...

Question

 For the molecule BF3, if we write the Lewis dot structure by first completing the octet around the pendant F atoms, we find that we have used all the valence electrons but the B has less than an octet (Structure A). Using our rules for drawing Lewis dot structures, we complete the octet around the B by forming double bonds from one of the F atoms which give rise to the resonance structures shown in Structure B. Structural characterization of BF3 suggests that there are no double bonds to F and that Structure A is the actual structure even though is does not obey the octet rule. In this case we can justify this structure based on Formal Charge arguments. Determine the formal charge on all the atoms in the electron deficient structure, Structure A, and on one of the resonance structures in Structure B and, using the rules of Formal Charge, tell why Structure A is the preferred one.