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

The chemical formula for phosphorus trichloride PCl3 is a flaming yellow liquid. This liquid might also be colourless. PCl3 is a poisonous liquid having a foul odour. This chemical has a molar mass of 137.33 g/mol. This compound’s melting point and boiling point are -93.6°C and 76.1°C, respectively.

Concerns can now be raised regarding the polarity of this molecule. Is PCl3 polar or nonpolar? Not to worry, the solution is straightforward! Because of its geometry and the difference in electronegativity between its two atoms, PCl3 is a polar molecule.

Again, another question, such as whether PCl3 is ionic or covalent, may arise. Therefore, PCl3 is a covalent molecule, as the link between phosphorus and chlorine is formed by the equal sharing of electrons.

Let’s move on to the preparation phase. Phosphorus trichloride can be made by treating chlorine with a solution of white phosphorus in PCl3 that is refluxing.

Moreover, PCl5 production is likely throughout this procedure. For this reason, continual elimination of phosphorus trichloride is required.

P4 + 6Cl2 ——–> 4PCl3

As with any other compound, this has a wide range of applications. From being employed in reactions to producing something, PCl3 can serve a variety of purposes.

It is essential to understand the structure, hybridization, and bonding of this liquid prior to initiating reactions involving PCl3.

Therefore, without further ado, let’s dive into these issues in depth!

Drawing Lewis Structure

A Lewis structure is primarily concerned with completing the octet of atoms in a molecule. This assists the atoms in attaining stability.

The lewis structure of any chemical allows us to determine the amount of bonds, types of bonds, and interatomic interactions.

Now, in order to simplify the process of designing a Lewis structure, I will list the processes in bullet points:

Totalize the number of valence electrons present in the molecule. Be cautious with + and – signs. A ‘+’ signifies electron loss, whereas a ‘-‘ signifies electron gain.

Determine the centre atom, or the atom with the greatest number of bonding sites.

Develop a skeleton with only single linkages.

Complete the atom’s octet with the remaining electrons. Always begin with electronegative atoms, followed by electropositive atoms.

Check whether multiple bonds are required for all atoms to satisfy the octet rule.

At the conclusion, verify that each atom has the lowest possible formal charge. Calculating formal charge is possible using the following formula:

Now let’s proceed to the PCl3 Lewis structure.

Lewis Structure of PCl3

PCl3’s lewis structure can be described as follows:

To create the Lewis structure, we must first add up the valence electrons of each atom.

Here,

Phosphorous equals five valence electrons.

Chlorine = 7 valence electrons

3* Cl = 7*3 = 21

So total valence electrons = 26

We must now consider the core atom. Essentially, the central atom is the atom with the greatest number of bonding sites.

Phosphorous is the central atom in this case.

To depict the final lewis structure of PCl3, we must now begin with the skeletal framework.

The skeletal structure is depicted using only single bonds.

This is PCl3’s skeletal structure.

The next step is to use the remaining electrons to complete the octet of the atoms.

The solitary bonds in the skeletal structure require six electrons. Therefore, 20 electrons remain to be distributed among the atoms.

After completing the electrons, the final Lewis structure of PCl3 is seen.

Finally, to ensure that the lewis structure is accurate, we must examine the octet and formal charge of each atom. Every atom should have the smallest formal charge feasible.

In addition, each atom in the lewis structure of PCl3 has eight electrons after sharing, completing an octet.

Let’s move on to the phosphorus trichloride hybridization.

PCl3 Hybridization

Sp3 is the hybridization product of PCl3

In general, the hybridization of a molecule provides information about the mixing of orbitals in a compound.

This concept can be comprehended using either the concept of bonding or a straightforward formula.

First, let’s examine the bonding component.

The Lewis diagram reveals that in PCl3, phosphorus forms three sigma bonds with three chlorine atoms. This results in the presence of two lone pairs on the phosphorus atom.

This idea describes the hybridization of sp3 PCl3 extremely well.

Another simple formula can also provide us with the PCl3 hybridization This formula can be used to determine the hybridization of any chemical, not just PCl3.

H = ½ [ V+M-C+A]

Here,

H= Hybridization

V equals the number of valence electrons

M = number of univalent atoms

C = the charge of a cation

A = anion’s charge

If H= 2 = Sp

Hybridisation H= 3 = Sp2

hybridisation H= 4 = Sp3

Hybridization H= 5 = Sp3d

H= 6 = Sp3d2 hybridization

Let’s use this formula to determine the PCl3 hybridization.

V (valence electron of central atom) = 5 in this case.

M (monovalent atom) = Cl = 3

Since it is a neutral molecule, both C and A will equal zero.

Thus , H= ½ [5+3] = ½ * 8

= 4 = Sp3

These two hypotheses describe Sp3 hybridization of PCl3 in detail.

PCl3 Molecular Geometry

PCl3 has the chemical shape of a trigonal pyramid.

The molecular geometry of any substance can be easily predicted using the VSEPR theory. The linked VSEPR chart provides insight into this;

Now PCl3 is a molecule of type AX3E, where A is the core atom, X is the surrounding atom, and E is the lone pair. PCl3 has one lone pair and three neighbouring atoms.

Thus, it is evident from the graph that the molecular geometry of PCl3 is a trigonal pyramid.

PCl3’s electron geometry is also tetrahedral. Currently, there exists a distinct distinction between electron geometry and molecular geometry.

When establishing the shape, molecular geometry does not account for lone pairs. Although electron geometry includes lone pairs.

The bond angle of PCl3 is 103 degrees. Due to the repulsion between the lone pairs on phosphorus, the bond angle of trigonal pyramidal compounds is less than ideal (109 degrees)

PCl3 Molecular Orbital (MO) Diagram

In a molecular orbital diagram of PCl3, three bonding orbitals are depicted as being filled. And three anti-bonding orbitals will be vacant.

The hybridization reveals that three Sp3 hybrid orbitals of phosphorus will be filled by three Cl atoms. The remaining orbital is a non-bonding, double-field orbital that represents the phosphorus pair.

Below is the MO diagram for PF3, from which you can simply get the MO diagram for PCl.

A MO diagram provides information regarding the bonding, bond order, bond angle, and bond length of any chemical. The linked video clip provides general information about the Lewis structure.

The Polarity of PCl3

Due to the lone pair present on the top of the Phosphorus atom and its tetrahedral electron shape, Phosphorus trichloride is regarded to be a polar molecule.

Consequently, the overall distribution of charge across the molecule is non-uniform, leading in the development of a polar molecule.

I had previously prepared a comprehensive paper on the polarity of PCl3.

Utilization of PCl3

It is soluble in benzene, ether, CS2, and other polar chemicals since it is a polar molecule.

This substance is also employed as an electrophile in numerous chemical processes.

It is widely employed in the synthesis of several organophosphorus chemicals.

This chemical acts as a nucleophile due to the presence of a lone pair, or Lewis base.

It is used extensively in the production of pesticides and insecticides.

Conclusion

Before moving on to the reactions, this article provides an overview of PCl3’s fundamentals. It describes the basic structure of PCl3 and its drawing fundamentals. In addition, it clarifies PCl3’s hybridization and molecular geometry.

If you have any questions, please feel free to contact me at any time.

Read more: Is NH4+ a base or an acid?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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