do you mean BF4^-? because that would answer your 3 outer electron question, as the minus charge means an extra electron is present, which would provide the one electron each for each flourine. Alternatively it could be BF3, which a dative covalent bond with flourine, as opposed to the B having an extra electron. This seems more likely to me .
The shape I would say tetrahedral as you have the four outer atoms, but the bond angles would be slightly squashed on the non datives.
I think thats right. Someone correct me if I'm wrong.
This is so embarrassing btw but what the heck, might aswell say it out load! ITS OFFICIAL. I am obsessed with the way Trigonal is pronounced. The word sounds sooo posh... like some kind of a drug! yummyy. Trigonalllllll… :P
BF4- is tetrahedral with NO distortion. The atoms themselves make no distinction between normal covalent and dative covalent bonds. These are just ideas to help us explain where the electrons have come from. Once the molecules or ions are formed the electrons are perfectly symmetrical.