MO Diagram, PCl5 Lewis Structure, Molecular Geometry, and Hybridization

The chemical elements Phosphorus (Atomic number: 15, symbol: P) and Chlorine combine to make Phosphorus Pentachloride (PCl5) (Atomic number: 17, symbol: Cl).

A molecule of Phosphorus Pentachloride has one atom of phosphorus and five atoms of chlorine.

When it comes to the compound’s physical appearance, it is colourless and sensitive to water and moisture in its solid form.

Despite the fact that it is colourless, commercial specimens have become green or yellow after being polluted by Hydrogen Chloride (HCl).

It can also be found in liquid and gaseous forms, where it has neutral characteristics. It has a crystalline salt-like structure and an irritant odour when solid.

Phosphorus Pentachloride gasifies nearly barren of any separation of phosphorus trichloride or chlorine gas in the environment, according to the mass action law.

The molecular weight of PCl5 is 208.24 grammes per mol. It has a boiling temperature of 166.8 degrees Celsius, which is greater than water, and a melting point of 160.5 degrees Celsius.

It also has Lewis acidity qualities because to its use in chlorination, hydrolysis, and other processes.

PCl5 is created in chemistry by the process of self-ionization. The following are its chemical equilibrium equations:

PCl4+     +     Cl-      ⇌     PCl5

PCl5 Lewis Structure

The Lewis structure of a compound is the arrangement of the valence shell electrons of its underlying atom.

Dots are used to represent electrons in Lewis structures, and bonds between various electrons are represented by a straight line with a set of electrons at the end.

The ultimate goal of creating a Lewis structure is to evaluate and arrive at a configuration that holds the best arrangement of electrons and so maintains equilibrium.

This must be done while keeping the octet rule and the concepts of formal charges in mind.

The 3-dimensional depiction of a compound’s constituents in space, as well as its molecular design and geometry, are not addressed by its Lewis structure.

The Lewis structure of PCl5 is depicted in this diagram.

Count the valence electrons in a PCl5 molecule in step one. For this, we can consult the periodic table. PCl5 is made up of Phosphorous and Chlorine, as we’ve learned.

The electron composition of phosphorus, which has the atomic number 15, is 2, 8, 5. It possesses 5 electrons in its outermost shell as a result.

Because of its atomic number 17 and consequent arrangement 2,8,7, chlorine has 7 electrons in its outermost shell.

Step 2: Each of the 5 Chlorine atoms will make a connection with Phosphorus to provide stability.

Step 3: Each of the Chlorine atoms receives one of Phosphorus’ five valence shell electrons.

Step 4: The next step is to determine whether the atoms are stable. The valency of Phosphorus is 3, whereas the valency of Chlorine atoms is 1.

This may have been a problem, but because to its empty 3d orbital, it can retain the 5 chlorine atoms.

Step 5: When we visualise the figure, we see a Phosphorus atom in the centre, surrounded by five Chlorine atoms.

PCl5 Molecular Geometry

Molecular geometry is a two-dimensional figure similar to the one seen below.

In addition to serving as a three-dimensional representation of the data at hand, molecular geometry is required for observing and inferring the cause for a compound’s unique features.

It even shows the precise bond lengths and angles between two atoms, such as the bond angle and torsion angle.

The molecular representation also aids in comprehending the factors that lead an element to take on a given atomic arrangement and structure.

This 3-dimensional model can explain properties like magnetism, resistance, reactivity, potency, alignment, and physical features like colour, shape, and odour.

These features obviously determine a compound’s potential utility as well as how it will react when exposed to foreign or homogenous substances.

The following sorts of molecular models exist, each with its own set of characteristics:

Angular

Linear

Octahedral

Planar Trigonometry

Pyramidal Trigonal

When we talk about PCl5, the core atom, P offers each of the 5 Chlorine atoms 5 electrons. Each of the five Cl atoms contributes one electron.

This gives the valence shell electrons a total of ten. There are a total of 5 electron pairs in the valence shell. There are two types of P-Cl bonds in the PCl5 structure.

With the other bonds in the atom, all of the Phosphorus-Chlorine equatorial bonds form two 90-degree and 120-degree bond angles.

The axial bond is the second type of bond. With the supplemental bonds, each of these P-Cl bonds forms three 90-degree and 180-degree bond angles.

PCl5 hybridization

The need for a molecule to be stable and in equilibrium is the first and most important knowledge of VSPER theory and hybridization.

This notion asserts that atoms’ orbitals with equal or similar energy can fuse together, resulting in new, degenerate orbitals that are hybrid in nature.

These hybrid orbitals also have an impact on a compound’s molecular shape, reactivity, and bonding properties.

Hybridization, along with quantum mechanics, is a well-studied topic in contemporary science.

Because of the energy and configuration of the outermost orbit of electrons in a compound, the new hybrid orbitals differ from the original ones.

Each atomic orbital has a different energy level, and the merger of orbitals should result in a charge balance.

The process can involve both fully filled and half-filled orbitals, depending on the presence of the underlying elements on the periodic table.

The following are examples of hybridizations:

SP

SP2

SP3

SP3D

SP3D2

SP3D3

Phosphorus and chlorine have s, p, and d orbitals because of their positions on the periodic table.

The 3d orbitals, like the 3p and 3s orbitals, as well as the 4p and 4s orbitals, have a similar amount of energy. This gives the hybridization a large number of orbitals to select from, including 3s, 3p, 3d, 4s, and 4p.

While 3d orbitals have a similar or equivalent amount of energy, the energy difference between 4s and 3p orbitals prevents the hybridization of 3d, 3p, and 4s orbitals.

The PCl5 molecule has a trigonal bipyramidal form. SP3D is the hybridization.

Let’s take a look at how this works:

Step 1: All of the 1s, 1d, and 3p orbitals are now hybrid. As a result, PCl5 can obtain 5 hybridised SP3D orbitals, each at one corner of the trigonal bipyramidal structure.

Step 2: Bond angles vary depending on the type of bond. There are five distinct SP3D orbits of Phosphorus that coincide with the p orbitals of Chlorine in Phosphorus Chloride.

The five bonds between Phosphorus and Chlorine are sigma bonds, and these P orbitals are completely occupied.

Because of the symmetric distribution of electron regions in the compound’s atoms, the PCl5 compound is non-polar in nature.

PCl5’s Atomic Bonds

Axial Bonds: Axial bonds make up two of the five Phosphorus-Chlorine bonds. One bond is located above the equator, while the other is located below it. Both bonds are at a 90-degree angle with the plane.

Equatorial Bonds: The final three bonds are all equatorial. The three bonds are in the same plane and form a 120-degree angle with one another.

The axial bonds between pairs are considerably extended because they must survive higher and more strenuous repulsiveness from the second type of bonds, the equatorial pairs.

As the distance between them grows, the bonds get weaker.

As a result, equatorial bonds are more powerful and reactive than axial ones.

PCl5’s Molecular Orbital Theory and MO Diagram

Molecular Orbital diagrams are used in Molecular Orbital theory to represent the status of electrons in an atom clearly.

While the Valence Bond theory and VSPER can give you a sense of an atom’s properties, they aren’t relevant for some compounds.

The MO diagram illustrates a molecule’s chemical and physical properties, such as bond length, bond energy, bond angle, and shape.

The steps for creating a PCl5 MO diagram are as follows:

Step 1: Identify each atom’s valence electrons. In PCl5, there are 5 atoms of P and 7 atoms of Cl for every 5 atoms of Cl.

Step 2: Determine whether the molecule is heteronuclear or homonuclear in nature. PCl5 is a heteronuclear protein.

Step 3: Next, fill orbitals with overlapping orbitals’ bonding and energy attributes.

Step 4: The bigger the number of nodes, the higher the MOs. Due to SP3D, PCl5 has a value of 5.

Step 5: MOs can now be filled with electrons after the schematic has been produced.

PCl5’s Applications

It is frequently employed as a chlorinating agent and is one of the most important phosphorus chlorides, alongside POCl3 and PCl3.

Its diverse character makes it ideal for the production of critical commodities like medicines and electrolytes for lithium-ion batteries. It also has a few more applications in the industry, as listed below:

It’s utilised to make dyestuff, organic compounds, and intermediates since it’s a good catalyst.

It’s also employed in the synthesis of acetyl cellulose as a catalyst. It is the projection film made of plastic on which movies and videos are printed.

It’s utilised in the pharmaceutical sector to make cephalosporin and penicillin, among other things.

It is also employed in the manufacture of acid chlorides and is an important aspect of organic chemistry.

PCl5 is also used as a catalyst in the cyclization and condensation processes.

Conclusion

The principles of Lewis Structure, Molecular Geometry, Hybridization, and Molecular Orbital theory can be used to understand the physical and reactive properties of PCl5 as well as its industry-wide applications.

PCl5 is employed in laboratories, pharmaceutical businesses, and industries, and its homogeneous structure allows for such a wide range of applications.

It’s also utilised as a catalyst in chemical reactions, and it even goes through a phase transition when exposed to higher concentrations:

PCl4+     +    PCl6-     ⇌     2PCl5

Read more: Apples: Acidic or Alkaline pH?

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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