Would the PF_2^+ molecule be trigonal planar or bent?

May 18, 2017

Well, how many valence electrons has we got? And I think you are right.

Explanation:

There are $5 \left(P\right) + 2 \times 7 \left(F\right) - 1 = 19 - 1 = 18$ $\text{electrons}$, which we distribute around 3 centres; i.e. 9 electron pairs........

And I make this: $F - {\ddot{P}}^{+} - F$.

There are 3 regions of electron density around the central phosphorus atom: the two $P - F$ bonds; and the lone pair. Electronic geometry is predicted to be trigonal planar; $\angle F - P - F > {120}^{\circ}$, due to the disproportionate influence of the $P$ lone pair.

Either your teacher got it wrong, or we have misinterpreted the problem. Both scenarios are possible.