Boron trifluoride, BF3, is often cited as an example of a molecule for which an octet on the central atom is not achieved. Two Lewis representations are proposed:
Representation X: Boron is surrounded by three single B—F bonds, each fluorine bearing three lone pairs. Boron has only six valence electrons around it.
Representation Y: One of the B—F bonds is drawn as a B=F double bond (by donating a lone pair from fluorine into a p orbital on boron), giving boron a complete octet. The formal charges are adjusted accordingly.
(a) Determine the formal charge on each atom in Representation X.
(b) Determine the formal charge on each atom in Representation Y.
(c) Identify which representation is more favorable and justify your selection using formal-charge analysis.
(d) Discuss why the less favorable representation might still contribute to the overall resonance hybrid, referencing orbital overlap and delocalization.