Chemistry · Chemical Bonding · NEET
PCl5 is trigonal bipyramidal (sp3d). Three P-Cl bonds lie in one flat middle plane and point 120 degrees apart. These are the EQUATORIAL bonds. The other two P-Cl bonds point straight up and straight down (perpendicular to that plane, 180 degrees apart). These are the AXIAL bonds. So: 3 equatorial + 2 axial = 5 bonds in total.
Bond length depends on how much repulsion the bonding electrons feel from nearby bonds. Count the bonds that sit at 90 degrees (the strongest repulsion angle). Each AXIAL bond has 3 neighbours at 90 degrees (the three equatorial bonds). Each EQUATORIAL bond has only 2 neighbours at 90 degrees (the two axial bonds). More 90-degree repulsion pushes the axial atom slightly away, so the axial bond is longer and weaker. Remember: more repulsion = longer, weaker bond.
Two bonds are longer. The 2 axial bonds are the longer ones (about 219 pm). The 3 equatorial bonds are shorter (about 204 pm). A common mistake is to say all 5 P-Cl bonds are equal because they are all 'P-Cl'. They are NOT equal in a trigonal bipyramid.
There are three angles. Equatorial to equatorial = 120 degrees (in the middle plane). Axial to equatorial = 90 degrees. Axial to axial (top to bottom) = 180 degrees. Because these angles are different, the bonds are not all equivalent, unlike in a symmetric shape such as SF6 (octahedral, all 90 degrees).
The two axial bonds are longer and weaker, so they break easily. In the solid, PCl5 even splits into ions. This weakness makes PCl5 a reactive chlorinating agent. So 'PCl5 is non-reactive' is a WRONG statement, which NEET has directly tested.
PCl5 is non-polar. Even though the axial and equatorial bonds differ in length, the shape is symmetric enough that the bond dipoles cancel out. Its net dipole moment is zero. The same is true for the similar molecules SbCl5 and PF5.
Identify the incorrect statement related to PCl5 from the following:
Match List-I with List-II. List-I: (a) PCl5, (b) SF6, (c) BrF5, (d) BF3. List-II: (i) Square pyramidal, (ii) Trigonal planar, (iii) Octahedral, (iv) Trigonal bipyramidal.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The axial P-Cl bonds are about 219 pm and the equatorial P-Cl bonds are about 204 pm. So the axial bonds are roughly 15 pm longer. You do not need exact numbers for NEET - just remember axial > equatorial in length.
PCl5 uses sp3d hybridisation. Phosphorus mixes one s, three p and one d orbital to make five sp3d hybrid orbitals that point to the corners of a trigonal bipyramid. Each overlaps with a p orbital of chlorine to form five P-Cl sigma bonds.
Yes. PF5, SbCl5 and other AB5 (sp3d) molecules show the same pattern: axial bonds are longer than equatorial bonds for the same reason - greater 90-degree repulsion on the axial positions.
A lone pair is more repulsive than a bond pair, so it prefers the roomier equatorial position (only two 90-degree neighbours). For bonds, the axial position is the more crowded one, which is why axial bonds are stretched longer. Both facts come from the same idea: 90-degree repulsion is strongest, and the equatorial site has less of it.
Yes. It is directly asked as a statement-based question (NEET 2022 and 2026) and supports many VSEPR and shape-matching questions. Knowing that axial bonds are longer and that PCl5 is therefore reactive can win you an easy mark.
