Question

question 19
4 pts
the shape of the phosphorus trifluoride molecule (pf₃) is,
bent
trigonal pyramidal
trigonal planar
tetrahedral
linear

Explanation:

To determine the shape of \(PF_3\), use VSEPR (Valence - Shell Electron - Pair Repulsion) theory.

• Phosphorus (\(P\)) has 5 valence electrons. Each fluorine (\(F\)) atom contributes 1 electron for bonding. So, the total number of valence electrons in \(PF_3\) is \(5+(3\times1)=8\).
• The number of bonding pairs (\(BP\)): There are 3 \(P - F\) bonds, so \(BP = 3\).
• The number of lone pairs (\(LP\)) on \(P\): Using the formula \(LP=\frac{\text{Valence electrons}-\text{Number of bonding electrons}}{2}\). The number of bonding electrons is \(3\times2 = 6\) (since each bond has 2 electrons). So \(LP=\frac{8 - 6}{2}=1\).
• According to VSEPR, for a molecule with \(BP = 3\) and \(LP=1\), the electron - pair geometry is tetrahedral (based on \(BP + LP=4\) electron pairs), but the molecular geometry (shape) is trigonal pyramidal (because we consider the positions of atoms only, and the lone pair distorts the ideal tetrahedral shape to give a pyramidal shape for the atoms).

Answer:

trigonal pyramidal