PCL Hybridisation Explained With Structure, Bonds, Polarity & Uses

Phosphorous pentachloride is an inorganic chemical compound with the molecular formula of PCl5. It mainly exists as a greenish-yellow crystalline solid. It has a strong irritating odour. The gaseous neutral molecule of phosphorous pentachloride has trigonal bipyramidal geometry due to its sp3d hybridization. It is one of the significant chlorides of phosphorus and is commonly used as a chlorinating agent and a catalyst in organic chemistry. This Chemistry article focuses on the meaning, explanation, shape, and geometry of PCl5 hybridization.

PCl5 Hybridization

Humphry Davy, an English scientist, developed the first PCl5 hybridization in 1808 which was not very accurate. Hence, Pierre Louis Dulong, a French chemist, provided the first accurate analysis of phosphorus pentachloride in 1816. PCl5 (Phosphorus Pentachloride) is a chemical compound made up of one phosphorus molecule and five chloride molecules. It is a colourless substance that is water and moisture sensitive. Phosphorus is the central atom of the compound which has five valence electrons. These electrons make bonds with five chlorine atoms. As a result, five sigma bonds are formed in PCl5 which results in the formation of sp3d hybridization.

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Some of the important hybridization including s, p, and d orbitals

Shape of Molecule	Types of Hybridization	Atomic Orbitals	Examples
Square planar	dsp2	d+s+p(2)	[Ni(CN)4]2−
Trigonal bipyramidal	sp3d	s+p(3)+d	PCl5
Square pyramidal	sp3d	s+p(3)+d	BrF5
Octahedral	sp3d2	s+p(3)+d(2), d(2)+s+p(3)	[CrF6]3-, [Co(NH3)6]3+

The structure PCl5 includes one phosphorus and five chlorine atoms. The chlorine atoms are connected to the phosphorus atom via five covalent (sigma) bonds.

PCl5 Hybridization of Central Atom

The central atom of PCl5 is phosphorus which has 5 valence electrons. Hence, it takes 5 more electrons from each chlorine atom to form a stable compound. The electrons from chlorine atoms are accepted in 3s, 3p, and 3d orbital. Therefore, the hybridization of PCl5 is sp3d.

Calculation of Hybridization

The hybridization of any compound can be calculated by using the following formula;

Hybridization=1/2[V+M-C+A]

Here, V is the number of valence electrons,

M is the number of monovalent atoms

C represents positive charge

A is the negative charge

Let us use this formula for 

PCl5 which has 5 valence electrons, 5 monovalent atoms attached to the central atom and n=zero negative or positive charges.

Hybridization = 1/2[5+5+0+0}

=1/2[10]

= 5

The hybridization number is 5. Therefore, the hybridization of PCl5 would be sp3d.

Preparation of PCl5

The most common process used to prepare phosphorus pentachloride is the reaction between phosphorus trichloride and dry chlorine. The reaction is given as;

PCl3(l)+Cl2(g)→PCl5(g)

Bonds in PCl5

In the structure of PCl5 all the P-Cl bonds are not similar. There are two different types of bonds;

• Axial Bonds
• Equatorial Bonds

Axial Bonds

The longer and less stable bonds in the structure of PCl5 are known as axial bonds. One of the two bonds lies above the equatorial plane and the other lies below the equatorial plane. These bonds form an angle of 90o with the equatorial plane.

Equatorial Bonds

The other three shorter and stable bonds in the structure of PCl5 are called equatorial bonds. These three bonds lie in one plane and make an angle of 120o with each other.

Polarity of PCl5

PCl5 is a non-polar compound. In its structure, the P-Cl bonds are polar but they are arranged in a symmetrical molecular geometry. As a result, the dipole moment of each bond gets cancelled out with no polar character left.

Properties of PCl5

The physical and chemical properties of PCl5 are discussed below:

Physical Properties 

• It exists as a greenish-yellow crystalline solid.
• It has a molecular weight of 208.2 g/mol.
• It has a density of 
• 2.1g/c
• m
• 3
• 2.1g/cm3.
• It has a melting point of 160.5 °C (320.9 °F; 433.6 K).
• It has a billing point of 166.8 °C (332.2 °F; 439.9 K).
• It reacts with water and is soluble in 
• CS2, chlorocarbons, and benzene.

Chemical Properties 

• It dissolves in water to form phosphoric acid and hydrochloric acid.

PCl5+4H2O→H3PO4+5HCl

• Phosphoryl chloride and thionyl chloride are formed after a reaction between phosphorous pentachloride and sulphur dioxide.

PCl5+SO2→SOCl2+POCl3

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