Best Overview: Is PCl3 Polar or Nonpolar? - Science Education and Tutorials

Phosphorus compounds are very different and inflammable in nature. Phosphorus trichloride has the chemical formula PCl3. All atoms belong to the non-metal family group in the periodic table and possess high electronegativity values. Students used to ask “Is PCl3 polar or nonpolar?”, “PCl3 Lewis Structure”, “PCl3 molecular geometry”, “PCl3 bond angle”, and “PCl3 polarity”. In this blog post, we are going to discuss the polarity of PCl3 in a detailed manner.

PCl3 is commonly appearing at ordinary temperatures and pressures, it exists as a liquid with a yellowish texture. PCl3 contains one phosphorus atom and three chlorine atoms. Phosphorus trichloride (PCl3) is corrosive to biological tissue and metals, and it can also cause fires when it comes into contact with wood, cotton, and other materials. The phosphorus atom stays the center of the molecule and the remaining three chlorine atoms. “Is PCl3 polar or nonpolar?”, to answer this question, we need a detailed analysis of the polarity of the PCl3 molecule.

Because of the tetrahedral structural form of phosphorus trichloride(PCl3). Chlorine has atomic number 17 in the modern periodic table and seven outermost valence shell electrons. It comes under the halogen family group in the periodic table. Similarly, phosphorus has atomic numbers 15 and five outermost valence shell electrons. Total electron counting, only two electron excess in chlorine as compared with phosphorus.

PCl3 molecule is formed by elements of the nitrogen and halogen family group in the periodic table. When PCl3 is exposed to air, it absorbs water quickly and produces white vapors that have a distinct odor and are toxic to breathe. Phosphorus trichloride (PCl3) can phosphoric acid when it reacts with water and undergoes hydrolysis. The phosphorus atom in the PCl3 molecule has an oxidation state of +3, while chlorine has an oxidation state of -1.

Is PCl3 polar or nonpolar, then? PCl3 (Phosphorus trichloride) is polar due to its tetrahedral geometrical shape caused by the presence of a lone pair on the phosphorus atom. Second, the difference in electronegativity between phosphorus and chlorine atoms causes the P-Cl bonds to become polar, causing the entire molecule to become polar as well, resulting in a net dipole moment of the PCl3 molecule is 0.97 D.

Table of Contents

Preparation and reaction of PCl3

Phosphorus trichloride(PCl3) is a bright yellowish liquid with a strong intense odor. It is created primarily through the chlorination of phosphorus. It is the heterogeneous reaction, phosphorus in the soft solid phase and chlorine in the gas phase. Initially, phosphorus reacted with chlorine gas formed phosphorus trichloride(PCl3).

It is an exothermic reaction. The chemical equation of phosphorus chlorination exothermic reaction is shown below.

P4 + 6 Cl2 —> 4 PCl3
Preparation of phosphorus trichloride(PCl3)

Reaction of PCl3:

Phosphorus reacted with water very vigorously. It undergoes an exothermic reaction. Hydrochloric acid and phosphoric acid are formed by this reaction

PCl3 + 3 H2O —> H3PO3 + 3 HCl
Phosphorus trichloride(PCl3) reacted with water

Phenol reacted with phosphorus trichloride forms triphenyl phosphite.

3 PhOH + PCl3 —-> P(OPh)3 + 3 HCl
Phosphorus trichloride(PCl3) reacted with phenol

Ethanol reacted with phosphorus trichloride in the presence of organic base and gives ethyl phosphite.

PCl3 + 3 EtOH + 3 R3N —-> P(OEt)3 + 3 R3NH⁺Cl⁻
Phosphorus trichloride(PCl3) reacted with ethanol

Aminophosphonates are synthesised from the organic amine, phosphorus trichloride, and formaldehyde. This types of chemical reaction is called as click chemistry. This materials are used as herbicides.

R2NH + PCl3 + CH2O —-> (HO)2P(O)CH2NR2 + 3 HCl
Aminophosphonates from Phosphorus trichloride(PCl3)

Phosphorus trichloride(PCl3) reacted with Grignard reagent gives triphenylphosphine.

3 PhMgBr + PCl3 —-> Ph3P + 3 MgBrCl
Grignard reagent with phosphorus trichloride(PCl3)

PCl3 Molar Mass Calculation

Phosphorus trichloride(PCl3) has a molecular mass of 137.33 g/mol, which may be computed as follows.

Mol mass of PCl3 = 1 * 30.9 (atomic mass of S) + 3 * 35.4 (atomic mass of Cl) = 137.33 g·mol−1.
PCl3 molar mass calculation

The chemical composition of the Phosphorus trichloride molecule is 3 chlorine atoms and 1 phosphorus atom in the middle.

PCl3 Lewis Structure: Is PCl3 polar or nonpolar?

The core central atom is phosphorus, which is flanked by three chlorine atoms. Phosphorus contains five outermost valence electrons, which means it contains five electrons in its outermost shell, whereas Chlorine has seven outermost electrons. chlorine atom is required one electron to complete the octet of chlorine atoms. If you want to know about the octet rule, please see in our previous post.

As a result of this, both two chlorine atoms form covalent bonds with the phosphorus atom, leaving the phosphorus atom with one lone pair. The bond pairs of P-Cl are repelled by the one lone pair on the phosphorus atom. According to VSEPR theory, electronic repulsion causes the molecule’s shape to tetrahedral, similar to that of the NH3 molecule.

The lone pair forces both two P-Cl bonds downward, resulting in the tetrahedral structural form of the PCl3 molecule. Because they generate electrical repulsion among the PCl3 molecule, lone pairs have deformed tetrahedral shapes of the PCl3 molecule.

Electronegative difference calculation PCl3:

When it comes to the electronegativity value of the PCl3 molecule, Chlorine has an electronegativity of 3.16, while Phosphorus has an electronegativity of 2.19. The electronegativity difference can be calculated by the following method.

Electronegativity value of chlorine = 3.16
Electronegativity value of phosphorus = 2.19
Difference of electronegativity value between phosphorus and chlorine = 3.16 -2.19=0.97
Electronegativity difference calculation of PCl3 molecule

The P-Cl bond of the PCl3 molecule becomes polar in nature due to this difference in electronegativity value. The power with which an atom can attract bound covalent electron pairs towards its side is known as the electronegativity of the atom.

As a result of this, the dipole moment of the P-Cl bond is non zero, and the dipoles of both P-Cl bonds are not negated due to the tetrahedral structure. The total dipole moment of the PCl3 molecule is calculated to be 0.97 D. Phosphorus atom receives a partial positive charge on it, while three chlorine atoms receive a partial negative charge on it.

PCl3 molecule’s electron dot structure is also known as PCl3 Lewis structure. It determines the number of outermost valence electrons and the electrons involved in the formation of the PCl3 molecule’s bonds. When discussing the Lewis structure of the PCl3 molecule, it is necessary to understand the outermost valence electrons of PCl3.

Phosphorus is the middle element of the molecule, with 5 electrons in its outermost valence electron shell, while chlorine atom is the outermost valence electron shell, with 7 electrons and one electron missing in the shell to complete its octet.

As a result of this above explanation, the PCl3 molecule contains a total of 26 valence electrons. The three chlorine atoms establish covalent connections with the phosphorus atom, leaving the phosphorus atom with one lone pair on it.

The lone pairs of phosphorus atom cause repulsion with P-Cl bond pairs, causing the P-Cl bonds to face downward force and the shape of the molecules to a tetrahedral pyramid like that of the NH3 (ammonia) molecule. The Cl-P-Cl bond has a bond angle of roughly 109 degrees. P-Cl bond has a bond length of 204 pm (picometer).

To sketch the PCl3 Lewis structure by following these instructions:

Step-1: Determine the total number of outermost valence shell electrons in the PCl3 molecule. The first step is to figure out how many outermost valence shell electrons there are in the PCl3 Lewis structure. A valence electron is one of an atom’s outermost shell electrons. In the Lewis diagram, it is represented by dots. The central phosphorus atom of the PCl3 molecule can be represented as follows

Look for the periodic group of each atom in PCl3 to determine its valence electron. phosphorus and chlorine are both members of the nitrogen and halogen family, which is the 15th and 17th groups in the periodic table respectively. Chlorine and phosphorus have seven and five valence electrons in their outermost shell respectively.

Because phosphorus and chlorine belong to the nitrogen and halogen family group in the periodic table, their valence electrons are five and seven respectively.

Total outermost valence shell electron of chlorine atom in PCl3 = 7
Total outermost valence shell electron of phosphorus atom in PCl3= 5
The PCl3 molecule has one central phosphorus atom and three chlorine atoms. Then the total outermost valence shell electrons can be calculated as follows
∴ Total outermost valence shell electrons available for PCl3 Lewis structure( dot structure) = 5+ 7*3 = 26 valence electrons in PCl3
calculation of total valence electron of PCl3 molecule

Step-2: Locate the atom with the least electronegative charge and place it in the center of the PCl3 molecular geometry. In this phase, we’ll select the least electronegative atom in the PCl3 molecule to place in the Lewis structure diagram’s center. In the periodic table, the electronegativity value increases in order from left to right and decreases in order from top to bottom in periodic groups.

As a result, chlorine is the second atom in the halogen family group in the periodic table. Phosphorus comes second in the nitrogen family group. A phosphorus atom has a lower electronegative value than a chlorine atom. Furthermore, because chlorine is the most electronegative element in chemistry, it can never be the central atom in a PCl3 Lewis structure diagram. As a result of this, place phosphorus at the center of the PCl3 Lewis structure, with chlorine uniformly around it the bottom of the tetrahedral pyramid structure.

Step-3: Use three single bonds (P-Cl) to connect the outside and core atoms in the PCl3 molecule. Connect all outside atoms (Chlorine) to the core central atom (phosphorus) with three single bonds in this stage.

Count how many outermost valence shell electrons we’ve used so far in the PCl3 structure. Because each phosphorus atom is connected to a chlorine atom by three single (P-Cl) bonds, each connection contains two electrons. Those are called bond pairs.

So, from the total of 26 valence electrons available for the PCl3 Lewis structure, we employed 6 electrons for three single (P-Cl) bonds in the PCl3 molecule. There are still 20 valence electrons left in the PCl3 molecule. Where do we need to place them in PCl3 molecular geometry?

Step-4: Starting with the outer three chlorine atoms in the PCl3 molecule, place the remaining valence electrons. We always start inserting valence electrons from the exterior atom first in the Lewis structure diagram. As a result, first, wrap around the leftover valence electrons on each chlorine atom.

To complete its octet, the chlorine atom requires 8 electrons in its outermost valence shell. With the help of a single bond, each chlorine already shares two electrons. Put 6 electrons around each chlorine atom and you’re done with the chlorine in the PCl3 molecule.

In the PCl3 molecule structure above, we’ve put 18 electrons around the chlorine atoms, represented by a dot. As all chlorine atoms have 8 electrons in their outermost valence shell, each chlorine atom comfortably completes its octet stability in the PCl3 molecule.

Using the Lewis structure, count how many outermost valence shell electrons have been consumed so far. In the PCl3 molecular structure, 24 electrons are represented as dot structure, whereas three single bonds each contain 6 electrons. As an outcome of the calculation, the outermost valence shell electrons are 18+ 6 = 24.

So far, we’ve used 24 of the total 26 outermost valence shell electrons available for the PCl3 Lewis structure. But now the question is, “How to fix the remaining four valence electrons?”. We also have two valence electrons to spare in the PCl3 molecule.

Step-5: Complete central phosphorus atom octet and use covalent bond if necessary. In the PCl3 Lewis structure, phosphorus is the central atom and it is connected with three single bonds (P-Cl) to the chlorine atoms. It means it already sharing 6 electrons with the help of 3 single bonds.

So, phosphorus is obeying the rule of the octet as 8 electrons around it. Place the two remaining valence electrons around the phosphorus center atom, which is acting as an octet stabilization in this case.

What are PCl3 electron and molecular geometry?

PCl3 has a tetrahedral pyramidal or trigonal pyramidal molecular geometry and ammonia like electron geometry, according to the VSEPR theory. Because the core central atom, phosphorus, has three P-Cl bonds with the surrounding three chlorine atoms in the bottom of tetrahedral geometry. In the same plane, the Cl-P-Cl bond forms a 109-degree angle. Because three chlorine atoms are in the same plane, they form a tetrahedral pyramidal or trigonal pyramidal shape.

Above that top of tetrahedral geometry, there is one lone pair. It maintains the tetrahedral-like form after connecting the upper one lone pairs to the trigonal pyramidal form. The lone pair is located just top to bond pairs in the tetrahedral geometry. The one lone pair of the electron is just above the trigonal pyramidal bond pair plane in the tetrahedral geometry.

Because of the one lone pair of electrons, it gives tetrahedral electron geometry. But the PCl3 molecular geometry is a trigonal pyramidal structural form in nature. It is the asymmetrical geometry of the PCl3 molecule. That makes, PCl3 molecule is polar.

How to find PCl3 molecular geometry

Determine the number of lone pairs on the PCl3 Lewis structure’s core phosphorus atom.
We need to figure out how many lone pairs there are on the central phosphorus atom of the PCl3 Lewis structure because the lone pairs on phosphorus are primarily responsible for the PCl3 molecule geometry distortion.

Use the formula below to find the lone pair on the PCl3 molecule’s center phosphorus atom.
L.P(P) = V.E(P) – N.A(P-Cl)/2

Lone pair on the central phosphorus atom = L.P(P)
The core central phosphorus atom’s valence electron = V.E(P)
Number of P-Cl bonds = N.A (P-Cl)
calculation for phosphorus atom lone pair in PCl3 molecule

In the case of PCl3, the center atom, phosphorus, has five outermost valence shell electrons and three chlorine atoms connected to it.

As a result of this, L.P(P) = (5 – 3)/2=1

The lone pair on the center phosphorus atom of the PCl3 electron geometry structure is equal to one. It means, the central phosphorus atom contains one lone pair.

Determine the number of PCl3 molecular hybridizations.
How to find the hybridization of the PCl3 molecule?. Now we need to figure out what PCl3’s molecular hybridization number is.

The formula of PCl3 molecular hybridization is as follows:
No. Hyb = N.A(P-Cl) + L.P(P)
No. Hy= the number of hybridizations
Number of P-Cl bonds = N.A (P-Cl)
Lone pair on the central phosphorus atom = L.P(P)
Calculation for hybridization number for PCl3 molecule

Phosphorus, then, is a central atom with three chlorine atoms linked to it and one lone pair in the PCl3 molecule. Then the number of hybridization (No. Hyb) can be calculated as follows

No. Hyb = 3+1 =4

Number of hybridization for PCl3 molecule is four. one S orbital, and three p orbitals combine together to form the sp3 hybridization.

3. Use VSEPR theory to determine PCl3 molecular geometry shape

When the VSEPR theory is utilized to calculate the shape of the PCl3 molecule, the AXN approach is typically used.

The AXN notation is as follows:
The center phosphorus atom in the PCl3 molecule is denoted by the letter A.
The bound pairs (P-Cl) of electrons to the core atom are represented by X.
The lone pairs of electrons on the center phosphorus atom are denoted by the letter N.
Notation for PCl3 molecular geometry

We know phosphorus is the center atom with three bound (P-Cl) pairs of electrons and one lone pair. because of the PCl3 Lewis structure. PCl3 has the general molecular geometry formula AX3N1.

If the molecule has an AX3N1 generic formula, the molecular geometry will be trigonal pyramidal and the electron geometry will be tetrahedral, according to the VSEPR theory.

Name of Molecule	Phosphorus trichloride
Chemical molecular formula	PCl3
Molecular geometry of PCl3	Trigonal pyramidal
Electron geometry of PCl3	Tetrahedral
Hybridization of PCl3	Sp³
Bond angle (Cl-P-Cl)	109º degree
Total Valence electron for PCl3	26
The formal charge of PCl3 on Phosphorus	0

How to calculate the formal charge in PCl3 Lewis Structure?

The formal charge on the phosphorus central atom of the PCl3 molecule often represents the actual charge on that phosphorus central atom. The formal charge will be found on the central phosphorus atom of the PCl3 Lewis dot structure in the following calculation.

To calculate the formal charge on central phosphorus atom of PCl3 molecule by using the following formula:
The formal charge on phosphorus atom of PCl3 molecule= (V. E(P)– L.E(P) – 1/2(B.E))
V.E (P) = Valence electron in phosphorus atom of PCl3 molecule
L.E(P) = Lone pairs of an electron in the phosphorus atom of the PCl3 molecule.
B.E = Bond pair electron in P atom of PCl3 molecule
calculation of formal charge on phosphorus atom in PCl3 molecule

We have 5 valence electrons, 2 lone pair electrons, and six bonding electrons in the phosphorus central atom (three single bonds attached to chlorine) of the PCl3 molecule. Now put these value of the phosphorus atom in the above formula

Formal charge on phosphorus atom of PCl3 molecule = (5- 2-(6/2)) =0

The formal charge on central phosphorus atom of PCl3 Lewis structure is zero.

Lewis structure of some other related post in this blog. See more detail by clicking on it, H2O, BeCl2, SF4, NH3, XeF4, BF3, BrF3, BrF5, SO3,SCl2 and CH2Cl2 molecules.

The dipole moment of PCl3

The dipole moment of the PCl3 molecule can assist us in determining the polarity’s strength. The polarity of any molecule is proportional to its dipole moment. Because the form of PCl3 is asymmetric. The dipole moment of PCl3 does not cancel each other as a result of this.

The dipole moment of PCl3 can be calculated as follows
D(P-Cl) = Q(P-Cl) * R(P-Cl)
D(P-Cl) = Dipole moment of P-Cl bond in PCl3 molecule
Q(P-Cl) = Charge distribution in P and Cl atom of PCl3 molecule
R(P-Cl)= Bond length of P-Cl bond in PCl3 molecule
Dipole moment calculation of PCl3 molecule

Net dipole moment of PCl3 molecule is 0.97 D.

Why is PCl3 a polar molecule?

Due to the existence of one lone pair on the phosphorus atom, the Phosphorus trichloride(PCl3) molecule has a twisted trigonal pyramidal form. According to the VSEPR hypothesis, lone pairs and bond pairs repel each other, causing the P-Cl bonds to move the lower side of the tetrahedral molecular structure, resulting in a trigonal pyramidal molecule.

The dipole moment of P-Cl bonds does not cancel out as it does in asymmetric PCl3 molecules. PCl3 has a dipole moment of 0.97D across the entire molecule. The formation of a polar molecule is caused by the geometrical structure and the difference in electronegativity value of atoms in the PCl3 molecule.

Because of the asymmetric tetrahedral shape of the PCl3 molecule, the charge is dispersed non-uniformly among the phosphorus and three chlorine atoms, resulting in the formation of positive and negative poles across the PCl3 molecule.

Properties of PCl3 molecule

The properties of PCl3 are listed as follows

Phosphorus trichloride(PCl3) has a molecular mass of 137.33 g/mol.
It is a liquid with a colorless to yellowish texture at room temperature(25 C).
It has an odor that is comparable to that of HCl.
It generates HCl gas after a violent reaction with water and gives phosphoric acid.
PCl3 has a density of 1.574 g/cm3.
PCl3 has a melting point of 93.6 °C (136.5 °F) and a boiling point of 76.1 °C (169.0 °F).
Phosphorus trichloride(PCl3) has a vapor pressure of 13.3 kPa.
PCl3 has a dipole moment of 0.97 D.

Uses of PCl3 molecule

The uses of PCl3 are listed as follows

PCl3 is commonly used in the production of organic phosphites.
PCl3 is also employed in the manufacture of organophosphorus compounds.
Insecticides and pesticides are extensively manufactured using PCl3.
When PCl3 is oxidized, it produces POCl3, which is useful as a plasticizer for PVC and as a flame retardant.
PCl3 is also a reagent that can be employed directly in the chemical synthesis of phosphorus compounds.

Conclusion

Phosphorus trichloride is a chemical compound with three chlorine atoms and one lone pair on the Phosphorus atom. The chemical formula of phosphorus trichloride is PCl3. Molecular hybridization of PCl3 is sp3. The bond angle Cl-P-Cl of the PCl3 molecule is 109 degrees.

According to VSEPR theory, PCl3 has a tetrahedral form, and because chlorine is more electronegative than Phosphorus, it draws the bound electron pair to its side and accumulates partial negative charge, leaving a positive charge on the Phosphorus atom.

The PCl3 molecule is polar in nature due to its asymmetric form and difference in electronegativity. The formal charge on phosphorus of PCl3 molecule is zero.The dipole moment of PCl3 molecule is 0.97 D.

If you have any queries and doubts on this post, please leave the comment. We will response as soon as possible.

FAQ on “Is PCl3 polar or nonpolar?”

Is PCl3 a polar compound?

The presence of one lone pair of electrons at the top of the molecule causes electron-electron repulsion, making PCl3 is polar molecule. As a result, the melting point of phosphorus trichloride is -94°C and the boiling point is 76°C.