Phosphorus

To identify the incorrect statement related to the structure and properties of phosphorus pentachloride (PCl₅), let's analyze each option step-by-step:

1. Three equatorial P-Cl bonds make an angle of 120° with each other:
   • PCl₅ is a molecule with a trigonal bipyramidal geometry. In this structure, the three equatorial bonds indeed form angles of 120° with each other. Therefore, this statement is correct.
2. Two axial P-Cl bonds make an angle of 180° with each other:
   • The axial positions in a trigonal bipyramidal molecule are directly opposite each other, maintaining a linear arrangement. Hence, these two bonds are 180° apart. This statement is also correct.
3. Axial P-Cl bonds are longer than equatorial P-Cl bonds:
   • In PCl₅, due to the increased bond length caused by electron repulsion at the axial positions, the axial bonds are indeed longer than the equatorial bonds. This statement is correct as well.
4. PCl₅ molecule is non-reactive:
   • This statement is incorrect. PCl₅ is known to be very reactive. It readily undergoes hydrolysis and can react with a variety of nucleophiles due to the presence of empty d-orbitals in phosphorus, allowing it to accept additional bond pairs. Therefore, this is the incorrect statement.

In conclusion, the incorrect statement about phosphorus pentachloride (PCl₅) is that it is non-reactive. Understanding the geometry and typical reactivity of PCl₅ helps in assessing its chemical behavior.