Boron Trifluoride, BF3 (2)
To have +1 charge on F, with its very high electron affinity is not good. -ve charges best placed on atoms with high EA.
Similarly -1 charge on B is bad
NOT important Lewis structure
fc = 7 - 2 - 4 = +1 Fluorine
fc = 3 - 4 - 0 = -1 Boron