Question

P in $PC{{l}_{5}}$ $s{{p}^{3}}d$ hybridisation, which of the following statements is wrong about $PC{{l}_{5}}$ structure?
[A] Two P-Cl bonds are stronger and three P-Cl bonds are weaker.
[B] Two P-Cl bonds are axial and larger than three P-Cl equatorial bonds.
[C] $PC{{l}_{5}}$ has a trigonal bipyramidal geometry with non-planar structure.
[D] All of these

Answer 1

Hint: To solve this, use the VSEPR theory according to which u can find out the shape from the hybridisation. In $PC{{l}_{5}}$ there are 2 types of P-Cl bonds, axial and equatorial. The longer among them is the weaker bond and the shorter is the stronger bond as bond strength is inversely proportional to bond length. Also one axial bond is above the plane and the other is below.

Complete step by step answer:
Firstly let us draw the structure of $PC{{l}_{5}}$. The hybridisation of the central atom is given to us and we can know its structure from the hybridisation according to the VSEPR theory.
We know that VSEPR theory is valence shell electron pair repulsion theory. According to it for $s{{p}^{3}}d$ hybridisation the shape is trigonal bipyramidal and its coordination number is 5. In trigonal bipyramidal geometry, there are 2 different kinds of bonds – axial and equatorial.
Now, let us draw the structure of $PC{{l}_{5}}$. It has three equatorial bonds and two axial bonds.

The axial bonds are longer than the equatorial bonds. This is due to the greater electron repulsion of the equatorial bonds which is caused if the axial bonds are closer to them. The axial bonds make an angle of ${{90}^{{}^\circ }}$ to the equatorial bonds. The equatorial bonds make an angle of ${{120}^{{}^\circ }}$ with each other.
Now, let us discuss each option and see whether they are correct or not.
In the first option we have two P-Cl bonds that are stronger and three P-Cl bonds are weaker. As we have discussed above that there are 2 axial bonds and 3 equatorial bonds and the axial bonds are longer. We know that bond strength is inversely proportional to bond length. Therefore, the longer bond is not stronger. Therefore the statement is incorrect.
Then we have two P-Cl bonds that are axial and larger than three P-Cl equatorial bonds. We have discussed above that the axial bonds are longer. Therefore, this statement is correct.
And lastly we have $PC{{l}_{5}}$ has a trigonal bipyramidal geometry with non-planar structure. We can see from the discussion that the geometry is trigonal bipyramidal also the equatorial bonds are planar and one of the axial bonds lie above the plane and the other lies below the plane. Hence, the structure is non-planar. Therefore, this statement is also correct.
We can see from the above discussion that the first option is incorrect about $PC{{l}_{5}}$.
So, the correct answer is “Option A”.

Note: Phosphorus pentachloride is a chemical compound and is widely used as a chlorinating reagent. It converts carboxylic acids into acyl chlorides and also alcohols to alkyl chlorides.
 However, its structure depends upon the environment. In molten and gaseous state it has trigonal bipyramidal geometry and in solid state it becomes an ionic compound, $PC{{l}_{4}}^{+}PC{{l}_{6}}^{-}$ .