Question

In a change from$PC{l_3} \to PC{l_5}$. The hybrid state of $p$ change from:
A. $s{p^2}$ to $s{p^3}$
B. $s{p^3}$ to $s{p^2}$
C. $s{p^3}$ to $s{p^3}d$
D. $s{p^3}$ to $ds{p^2}$

Answer 1

$PC{l_3}$ is phosphorus trichloride and $PC{l_5}$ is phosphorus pentachloride. The addition of $C{l_2}$ with $PC{l_3}$ produces $PC{l_5}$. The presence of vacant d orbitals in phosphorus allows it to add the $C{l_2}$ atoms to the inner $d$ orbitals.

Complete step by step answer: Hybridization is the process of combining two different orbitals of atoms generating new orbitals which are different from atomic orbitals. These new orbitals are referred to as hybrid orbitals.
Phosphorus is an element in the periodic table with atomic number 16. The electronic configuration of element phosphorus ($P$) is:
$P{\text{ }}:{\text{ }}1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}$
Thus phosphorus has three unpaired electrons in the outer shell$p$. Further in phosphorus there are vacant $d$ orbitals present i.e. $3d$. Due to these $d$ orbitals the valency of the central atom can be extended and more atoms can be added to the phosphorus atom.
In $PC{l_3}$, phosphorus is the central atom which is attached to three chlorine atoms. The phosphorus has one lone pair available in the form of $s$ electrons. The three $p$ electrons are present in $3{P_x}$, $3{P_y}$, $3{P_z}$ orbitals. The $s$ and $p$ orbitals undergo hybridization to produce $s{p^3}$ hybrid orbitals of equal energy.
In $PC{l_5}$, phosphorus the central atom is attached to five chlorine atoms. Here the vacant $3d$ orbitals take part in hybridization to produce five hybrid orbitals. One of the two $s$ electrons moves to the $d$ orbital to produce five singly filled orbitals. Each of the orbitals accepts an electron from chlorine to form five sigma bonds. Thus the hybridization of phosphorus pentachloride is $s{p^3}d$.
Thus, option C is the correct answer, the hybrid state of $P$ changes from $s{p^3}$ to $s{p^3}d$.

Note: The number of hybrid orbitals will be equal to the number of atomic orbitals. Only orbitals of the same atom will undergo hybridization. The shape of the orbital can be predicted by knowing the hybridization of orbitals.