Chem Explorers

Uncovering the Fascinating Properties of Phosphorus Pentachloride

When it comes to chemical compounds, there are few as fascinating and complex as phosphorus pentachloride (PCl5). This compound has many unique properties that make it of interest to chemistry students, educators, and researchers alike.

In this article, we will delve into the Lewis structure of PCl5, the octet rule, and formal charges associated with this compound. We will also explore the hybridization of PCl5, the different types of bonds present in the compound, and its polar nature.

Lewis Structure of PCl5

The Lewis structure of a compound is a diagram that shows how the valence electrons of its atoms are used to form shared pairs. For PCl5, the central position is occupied by the phosphorus atom, which has five valence electrons.

To achieve a stable configuration, the phosphorus atom shares its electrons with five chlorine atoms, each of which has seven valence electrons. The result is a trigonal bipyramidal structure, with three P-Cl bonds in the plane, and two axial P-Cl bonds that are perpendicular to it.

This structure is in line with the octet rule, which states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight valence electrons.

Octet Rule for PCl5

The octet rule is a fundamental principle in chemistry that describes how atoms tend to achieve a stable configuration by having eight valence electrons around them. However, certain compounds like PCl5, violate the octet rule by having more than eight valence electrons around the central atom.

Compounds that have more than eight electrons around the central atom are known as hypervalent compounds. In PCl5, the phosphorus atom has ten valence electrons in total, giving it an expanded octet.

This expanded octet is achieved by using the d-orbitals of the phosphorus atom to form extra bonds with the chlorine atoms.

Resonance in PCl5

Resonance is a phenomenon that occurs when a molecule can be represented by more than one Lewis structure, all of which are possible, and which contribute to the actual structure of the molecule. In PCl5, ionic resonance structures are possible, where the lone pair on the phosphorus atom can be moved to one of the chlorine atoms, creating a double bond.

This results in a resonating hybrid structure of PCl5. As a hypervalent compound, resonance helps explain how PCl5 can achieve an expanded octet.

Formal Charges in PCl5

Formal charges are used to determine the electronic distribution within a molecule by calculating the charge on each atom when electrons are not shared equally. In PCl5, the formal charge of the phosphorus atom is calculated by subtracting the number of electrons it has in the Lewis structure from the number it would have in its free state.

This is equal to one for PCl5. The formal charge on each chlorine atom is zero since it has an equal number of electrons in the Lewis structure and its neutral state.

Hybridization of PCl5

Hybridization is the mixing of atomic orbitals to create new hybrid orbitals for bonding. In PCl5 the hybridization of the five orbitals occurs because of the five bonds that it forms with the five Chlorine atoms.

The hybridization of Phosphorus involves combining one s- and three p-orbitals to form hybrid sp3d orbitals. The hybrid orbitals are arranged tetrahedrally around the phosphorus atom, with three atoms in the plane of the paper and two perpendicular to it.

Such hybrid orbitals are essential for the orbital overlap and electron redistribution required for successful bonding.

Types of Bonds and Polar

Nature of PCl5

The bonds in PCl5 are covalent and, they consist of equatorial and axial bonds. The equatorial bonds lie in the plane of the molecule and are at an angle of 120 degrees with each other.

The axial bonds are perpendicular to the plane of the molecule and lie at an angle of 180 degrees to each other. Because of the asymmetry of the molecule, it is polar, meaning it has a net dipole moment.

It is this property that makes it interesting as it has significant implications in chemical reactions and compounds made from PCl5.


In conclusion, PCl5 is a fascinating molecule with unique properties that make it of interest to researchers, students, and educators. The Lewis structure of PCl5, the octet rule, and formal charges associated with this compound were all discussed.

We also explored the hybridization of PCl5, its different types of bonds, and its polar nature. The information presented here is essential for understanding PCl5 and its role in chemistry.

Uses and Properties of PCl5

Phosphorus pentachloride, or PCl5, is an important compound with many uses in chemistry. Its unique properties make it a valuable tool for researchers and students alike.

Here, we will delve into the various uses of PCl5, its nature, properties, and reactivity, among other essential aspects.

PCl5 Uses

PCl5 is a versatile compound with numerous applications in different industries. One of its most common uses is as a chlorinating agent, where it reacts with primary and secondary alcohols and other organic compounds to remove the oxygen and introduce chlorine.

This property makes it a vital component in the pharmaceutical and fine chemical industries, where selective chlorination or dechlorination is essential in synthesizing different compounds. In addition to being a chlorinating agent, PCl5 is also a useful dehydrating agent.

It has the ability to convert primary, secondary, and tertiary alcohols and carboxylic acids to haloalkanes and alkyl halides through an elimination reaction with the elimination of water. Its dehydrating property also makes it useful in preparing anhydrous hydrogen chloride for use in refining and in the plastics industry.

PCl5 serves as a useful catalyst when used in conjunction with different reagents, like Lewis acids and organometallic reagents. It does this by forming a stable complex with the reagent, thereby enhancing its selectivity and reactivity in chemical reactions.

Nature of PCl5

PCl5 is a reactive compound that needs to be handled with care. Contact with water or air results in the formation of phosphoric and hydrochloric acids, leading to a violent reaction.

Inhalation of PCl5 fumes can lead to respiratory problems and pose other health hazards. The axial bonds in PCl5 are longer in length than the equatorial bonds because of repulsive forces between lone pairs and bond pairs.

The equatorial bonds lie in the plane of the molecule, making them closer together, whereas the axial bonds are perpendicular to the plane, making them farther apart. The different bond angles of the axial bond and equatorial bond are another contributing factor to the difference in length.

PC15 storage requirements usually involve using stoppered bottles placed in a cool, dry place. Storing PCl5 in the lab requires special attention because of its reactivity with water molecules.

These bottles must be kept closed to prevent contact with air or moisture.

PCl5 as a Base or Acid

PCl5 acts as a Lewis acid, attracting an electron pair from a nucleophile or an electron-rich molecule to form a new covalent bond. The phosphorus atom in PCl5 has an empty orbital that can accept an electron pair donated by a nucleophile or a base.

Hence, PCl5 attracts and accepts electrons from other molecules to form electron-deficient, positively charged species in solution.

Best Way to Form PCl5

PCl5 is best prepared by reacting phosphorus trichloride (PCl3) and chlorine (Cl2) in a batch reactor. This reaction occurs in a gas-phase at 80-100 C and produces PCl5 as a vapor, which is then condensed to its liquid form.

In an inert atmosphere, the precursor gases are fed continuously into a reactor, where the reaction occurs and the mixture is condensed. This technique, known as continuous processing, is more efficient and produces a consistent output.

PCl5 Solubility in H2O

PCl5 does not dissolve in water because the compound is nonpolar, while water is a polar solvent. Polar solvents, like water, dissolve polar solutes, whereas nonpolar solutes dissolve in non-polar solvents.

This property makes PCl5 useful in extracting or purifying non-polar solvents and in dissolution or crystallization.

Reactivity of PCl5 and PCl3

PCl5 is more reactive than PCl3 because of its structure, which possesses an expanded octet. It has more electrons and hence, is more likely to participate in chemical reactions.

Additionally, its structure is more geometrically complex than that of PCl3. While both molecules share similar chemical properties, these differences contribute to PCl5’s greater reactivity in chemical reactions.

General Information on Phosphorus

Phosphorus is a reactive, non-metallic element with atomic number 15 and a chemical symbol P. It is essential for living organisms and has many industrial uses.

The abundance and worldwide distribution of phosphate rocks led to the development of phosphatic fertilizers that revolutionized agriculture. The human body has about 0.84% phosphorus by weight, making it the fifth most abundant element in the human body.

Phosphorus is found in the form of phosphate minerals in rocks and soils, making up about 0.1% of the Earth’s crust. It is commonly used in the production of useful alloys, like copper phosphide and aluminum phosphide.

It also finds application in matches, semiconductors, and detergents.


PCl5 is a versatile and fascinating compound with diverse applications across multiple industries. Careful handling and storage are necessary when working with this compound because of its reactivity with water and air.

PCl5 is an essential agent in various industries, including pharmaceuticals, fine chemicals, and plastics. Its unique properties make it a valuable tool for researchers and students in the world of chemistry.

In conclusion, phosphorus pentachloride (PCl5) is a compound with unique properties that make it valuable in various industries. Its Lewis structure, octet rule violation, and resonance contribute to its stability and reactivity.

PCl5 is used as a chlorinating and dehydrating agent, as well as a catalyst in chemical reactions. It requires careful handling and storage due to its reactive nature and contact with water.

Understanding the uses and properties of PCl5 allows for safe and efficient utilization in chemistry. Remember, PCl5 is a powerful tool, but caution must be exercised to harness its potential.


1. What are the primary uses of PCl5?

PCl5 is commonly used as a chlorinating agent, dehydrating agent, and catalyst in various industries, including pharmaceuticals and fine chemicals. 2.

Is PCl5 reactive? Yes, PCl5 is reactive and can react violently when it comes into contact with water or air.

Inhalation of its fumes can be hazardous. 3.

Why are axial bonds longer than equatorial bonds in PCl5? The repulsive forces between lone pairs and bond pairs in PCl5 result in longer axial bonds compared to equatorial bonds.

4. How should PCl5 be stored in a chemical lab?

PCl5 should be stored in stoppered bottles placed in a cool, dry place to avoid contact with air or moisture, which can trigger a violent reaction. 5.

Is PCl5 a base or an acid? PCl5 acts as a Lewis acid since it can accept an electron pair to form a new covalent bond.

6. What is the best way to form PCl5?

PCl5 is usually formed by reacting phosphorus trichloride (PCl3) and chlorine (Cl2) in a batch or continuous processing method. 7.

Is PCl5 soluble in water? No, PCl5 is not soluble in water due to its nonpolar nature, while water is a polar solvent.

8. How does the reactivity of PCl5 compare to PCl3?

PCl5 is more reactive than PCl3 due to its expanded octet and geometric complexity, leading to increased participation in chemical reactions. Remember to handle PCl5 with caution due to its reactivity, and its unique properties make it a valuable tool in various chemical applications.

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