BF3 is not a hypervalent molecule. If we break down BF3 and look at its atomic structure B has 6 electrons in its outermost shell. Thus, the octet of the central atom is not complete meaning the valence shell have less than 8 e- electrons. Now if we recall the definition of a hypervalent molecule it is described as a molecule containing one or more main group elements with more than eight electrons in its valence shells.
