[Rick]

I've read that boron trifluoride is especially stable due to it's stronger bonds, and these bonds are strong dude to the ability of the flat molecule to form an empty pi bond/orbital.

How does this bond contribute to the stability if it is empty? is it because it's a LUMO?

[Mitch]

The more s character of a bond the stronger it is. BF₃ uses sp² bonds, unlike CF₄ which would use sp³.

[phth]

It has to do with the relative energy of the fluorine lone pairs and the relative energy of the vacant p-orbital.  Going to a larger halogen like chlorine or bromine, the bond becomes weaker because the constructive interference between the orbitals is less when the electrons move farther away. https://en.wikipedia.org/wiki/HSAB_theory (HSAB is not a theory BTW).