PCl3 Lewis Structure, Hybridization, Molecular Geometry, and MO Diagram

pcl3 geometry

Phosphorus trichloride with a chemical formula PCl3 is a yellow fuming liquid. This liquid can be colorless as well. PCl3 is a toxic liquid with an unpleasant smell. The molar mass of this compound is 137.33 g/mol. The melting point and boiling point of this compound are -93.6℃ and 76.1℃ respectively.

Now there can be questions about the polarity of this compound. Is PCl3 polar or nonpolar? Don’t worry, the answer is simple! PCl3 is a polar molecule because of its geometry and difference in electronegativity between the 2 atoms.

Again another question like, whether PCl3 is ionic or covalent, can pop up in your mind. So, PCl3 is a covalent molecule because here equal sharing of electrons forms the bond between phosphorus and chlorine.

Now let’s come to the preparatory part. Phosphorus trichloride can be produced by the treatment of chlorine with a refluxing solution of white phosphorus in PCl3.

Also, there is a high chance of PCl5 formation in this process. So to avoid that continuous removal of phosphorus trichloride is mandatory.

P4     +    6Cl2    ——–>    4PCl3

Like any other compound, this also has immense use in different fields. From being used in reactions to the production of something PCl3 can be used for different needs.

But before going into reactions involving PCl3, it is very necessary to know about the structure, hybridization, and bonding of this liquid.

So without any further ado let’s jump into these topics in detail!

 

How to Draw Lewis Structure

A lewis structure mainly focuses on fulfilling the octet of the atoms in a compound. This helps the atoms to gain stability.

The lewis structure of any compound helps us to find out the number of bonds, types of bonds, and the interaction between the atoms in a compound.

Now to simplify the process of drawing a lewis structure I have jotted down the steps in bullets:-

  • Sum up the total number of valence electrons in the molecule. Be careful about +, – signs. A ‘+’ sign means losing electrons and ‘-‘ means gaining.
  • Identify the central atom; the atom with the highest bonding sites.
  • Create a skeleton containing only single bonds.
  • Complete the octet of the atoms with the electrons left. Always begin with the electronegative atoms and then the electropositive ones.
  • Check if there is a requirement of multiple bonds for fulfilling the octet rule of all atoms.
  • At the end check that all the atoms are in their lowest possible formal charge. The calculation for formal charge can be done using the formula given below:-

Formal charge

Now let’s move on to the lewis structure of PCl3.

 

PCl3 Lewis Structure

The lewis structure of PCl3 can be explained as follows :

pcl3 lewis structure

To draw the lewis structure, first of all, we need to sum up the valence electrons of all the atoms.
Here,

Phosphorous = 5 valence electrons
Chlorine = 7 valence electrons
3* Cl = 7*3 = 21
So total valence electrons = 26

Now we need to consider a central atom. The central atom is basically the atom with the highest number of bonding sites.

Here the central atom is phosphorous.

Now to draw the final lewis structure of PCl3, we need to start from the skeletal structure.

The skeletal structure is drawn with single bonds only.

This is the skeletal structure of PCl3.

The next job is to fulfill the octet of the atoms with the remaining electrons.

For the single bonds in the skeletal structure, 6 electrons are used. So, 20 electrons are remaining which needs to be given around the atoms.

After fulfilling the electrons we can see the final lewis structure of PCl3.

Lastly, to ensure the lewis structure is completely correct, we need to check the octet of every atom and also their formal charge. Every atom should be in its least possible formal charge,

Also, every atom in the lewis structure of PCl3 is fulling octet, as they are having 8 electrons each after sharing.

Let’s move to the hybridization of phosphorus trichloride.

 

PCl3 Hybridization

The hybridization of PCl3 is Sp3.

The hybridization of a molecule generally gives us ideas about the mixing of orbitals in a compound.

We can understand this concept with the help of either the concept of bonding or by using a simple formula.

First, let’s understand the bonding part.

We can clearly see from the lewis diagram that in PCl3, phosphorus is forming three sigma bonds with 3 chlorine atoms. With that 2 lone pairs are present on the phosphorus atom.

 

 

Phosphorus electronic configuration

PCl3 electronic configuration

This concept very well explains the hybridization of PCl3 which is sp3.

Another simple formula can also give us the hybridization of PCl3. Not only PCl3, but this formula can also be used to find the hybridization of any compound.

H = ½ [ V+M-C+A]

Here,
H= Hybridization
V= No. of valence electrons
M= no. of monovalent atom
C= charge of cation
A= charge of anion

If, H= 2 = Sp hybridization
H= 3 = Sp2 hybridization
H= 4 = Sp3 hybridization
H= 5 = Sp3d hybridization
H= 6 = Sp3d2 hybridization

Let’s apply this formula to find the hybridization of PCl3

Here, V (valence electron of central atom) = 5
M ( monovalent atom) = Cl = 3
As it is a neutral compound thus C and A will be 0

Thus , H= ½ [5+3]
= ½ * 8
= 4 = Sp3

These two concepts clearly explain the Sp3 hybridization of PCl3.

 

PCl3 Molecular Geometry

The molecular geometry of PCl3 is a trigonal pyramid.

The molecular geometry of any compound can be determined easily from the VSEPR theory. The below-attached VSEPR chart gives us an idea about that;

VSEPR chart
Now PCl3 is a AX3E type molecule where, A = central atom, X = surrounding atom, E = lone pair. PCl3 has 1 lone pair and 3 surrounding atoms.

Thus the chart clearly shows that the molecular geometry of PCl3 is a trigonal pyramid.

Also, the electron geometry of PCl3 is tetrahedral. Now there is a clear difference between electron geometry and molecular geometry.

Molecular geometry does not consider the lone pairs while determining the shape. While electron geometry does include lone pairs.

PCl3 has a bond angle of 103 degrees. The decrease from the ideal bond angle of trigonal pyramidal compounds (109 degrees ) is due to repulsion between the lone pairs on phosphorus.

 

PCl3 Molecular Orbital (MO) Diagram

In a molecular orbital diagram of PCl3, we can see 3 bonding orbitals, which will be occupied. And 3 anti-bonding orbitals which will be empty.

We can see from the hybridization that 3 Sp3 hybrid orbitals of phosphorus will be occupied by 3 Cl atoms. The remaining one is a non-bonding orbital but doubly field, which denotes the lone pair of phosphorus.

Given below is the MO diagram of PF3 taking reference to which you can easily draw for PCl3.

 

pf3 MO diagram

A MO diagram helps us to know about the bonding, bond order, bond angle, and bond length of any compound. Below is the video snippet attached for the overall information of lewis structure.

 

PCl3 Polarity

The Phosphorus trichloride is considered a polar molecule because of the lone pair present on the top of the Phosphorus atom and its tetrahedral electron geometry.

As a result, the overall charge distribution across the molecule is non-uniform resulting in the formation of a polar molecule.

I have already written a detailed article on the polarity of PCl3.

 

 

Uses of PCl3

  • Being a polar molecule, it is soluble in benzene, ether, CS2, and other polar substances.
  • This compound is also used as an electrophile in many chemical reactions.
  • It is widely used for the formation of various organophosphorus compounds.
  • This compound also acts as a nucleophile as it has a lone pair ie; lewis base.
  • It is widely used in the manufacturing of pesticides insecticides.

 

Conclusion

This article covers all the basic things we need to learn about PCl3 before moving on to the reactions. It explains the lewis structure of PCl3 and its fundamentals to draw it. And, it makes you understand the hybridization and molecular geometry of PCl3.

Hope it was helpful and if there is any doubt feel free to contact me anytime.

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