Polar or nonpolar is PCl3?

PCl3 is the chemical formula for the phosphorus trichloride substance. Exists as a colourless to yellow fuming liquid and is poisonous in its natural state. Many of you may be curious as to whether or not PCl3 is a polar chemical. I will address this question and discuss its qualities and applications in the following post.

Consequently, is PCl3 polar or nonpolar? PCl3 is a polar molecule due to its tetrahedral geometrical shape with a lone pair on the Phosphorus atom and the difference in electronegativity between the Chlorine(3.16) and Phosphorus(2.19) atoms, which results in unequal sharing of electrons and the development of positive and negative poles across the molecule.

The IUPAC designation for phosphorus trichloride is Trichlorophosphane. Other names include

Chloride of Phosphorus(III) and Chloride of Phosphorus.

It occurs as a liquid at normal temperature and has a colourless to yellowish appearance. It is also regarded to be poisonous to biological organisms.

It has an odour similar to that of HCL. It is naturally volatile and strongly interacts with water to form HCl gas.

The molecular mass of PCl3 is 137.33 grammes per mole. It is computed as follows:

Mol mass of PCl3 = 1 x 30.9 x 35.4 (Mol mass of P and Cl, respectively) = 137.33 g/mol.

Phosphorus trichloride contains one Phosphorus atom and three Chlorine atoms, according to its chemical composition.

All three chlorine atoms are covalently bonded to the phosphorus atom, completing its octet and leaving the phosphorus atom with a lone pair.

Due to the lone pair on the Phosphorus atom and the repulsion between lone pairs and bond pairs, the form of the molecule changes to tetrahedral, with all three chlorine atoms at the three vertices of the pyramid and Phosphorus at the top.

In the PCl3 molecule, the phosphorus atom has an oxidation state of +3, whereas the chlorine atom has an oxidation state of 1.

In addition, Phosphorus has an electronegativity of 2.19 and Chlorine has an electronegativity of 3.19.

Being more electronegative, the chlorine atom attracts the bound electron pair to its side and acquires a partial negative charge, whereas the phosphorus atom acquires a partial positive charge.

Polar v/s Nonpolar Molecules

Different sorts of bonds, including ionic, covalent, metallic, and hydrogen, hold the molecules together. Covalent bonding can be polar or nonpolar based on the characteristics outlined in the following sections.

Let us examine the differences between polar and nonpolar molecules.

Polar Molecules: Polar molecules are molecules with an unequal distribution of charge on their atoms.

These molecules contain atoms with differing electronegativity and uneven numbers of bound electrons.

It is frequently observed that the geometrical shape of polar molecules is asymmetric, resulting in the uneven distribution of charge on the molecule.

Polar molecules’ dipole moments are always greater than zero. Examples of polar molecules include OF2, CH2O, and others.

You can investigate the cause of CH2O’s polarity.

Nonpolar Molecule: These are molecules in which the atoms have an equal distribution of charge.

In most circumstances, the electronegativity of atoms in these compounds is identical. And because the geometrical form of nonpolar molecules is always symmetric, the charge distribution on their atoms is evenly distributed.

Nonpolar molecules have a dipole moment that is always equal to zero.

Examples of nonpolar compounds include CS2, O2, and others. You can investigate the reason for CS2’s non-polarity.

PCl3 is a Polar Molecule, but why?

The molecule of phosphorus trichloride consists of three chlorine atoms and one phosphorus atom. As noted previously, the polarity across the P-Cl bond is caused by the difference in electronegativity between chlorine and phosphorus.

All three P-Cl bonds are polar because each chlorine atom has a partial negative charge and each phosphorus atom has a partial positive charge.

Phosphorus atoms also include a lone pair, and according to the VSEPR theory, there is repulsion between lone pairs and bond pairs. As a result, the three P-Cl bonds experience a downward force, resulting in a deformed shape.

In addition, the PCl3 molecule has a tetrahedral geometry, with all three chlorine atoms on one side (at the three vertices of the pyramid) and phosphorus in the centre (at the top corner of the pyramid).

Consequently, the dipole of the molecules is non-zero and originates from the downward direction of chlorine atoms.

The PCl3 molecule is hence polar.

Key Elements to Determine Polarity

If you wish to evaluate the polarity of a molecule, there are a few factors to consider in order to determine whether or not a molecule is polar.

Electronegativity: An atom’s electronegativity is its ability to attract bound pairs to its side. Greater an atom’s electronegativity, the greater its polarity.

If there is a difference in the electronegativity of the two atoms making a covalent connection, the resulting bond will be polar, and vice versa.

Polarity of a covalent bond is proportional to the difference in electronegativity between the atoms.

Here, Cl is more electronegative than P; hence, the P-Cl bond is polar.

Dipole Moment: A molecule’s polarity is measured by its dipole moment. It is determined by multiplying the atomic charge by the distance between the centres of positive and negative charge.

D = Q * R

Denoted by the letter D, its SI unit is the Debye. A polar molecule’s dipole moment is always greater than zero, whereas nonpolar molecules’ dipole moments are always equal to zero.

Given that PCl3 is a polar molecule, its dipole moment is 0.97 D.

The polarity of a molecule can be determined by the molecule’s geometrical shape, which is a crucial physical feature.

In general, polar molecules are observed to have asymmetric or deformed geometrical structures, whereas nonpolar molecules have symmetrical geometrical shapes.

It is also feasible for a polar link to exist within a nonpolar molecule, but its polarity is nullified by its symmetric structure.

The 3D geometrical geometry of the PCl3 molecule is depicted here. You must read the article on PCl3 lewis structure, Geometry, for additional information.

Preparation

In industry, it is produced by reacting chlorine with a solution of white phosphorus in the presence of phosphorus trichloride while removing PCl3 continuously to prevent the production of PCl5.

P4 (Phosphorus) + 6 Cl2 (Chlorine) (Phosphorus trichloride)

Qualities of PCl3

137.33 g/mol is the molecular mass of phosphorus trichloride.

It occurs as a liquid with a colourless to yellowish consistency at normal temperature.

It has an odour comparable to that of HCl.

It aggressively interacts with water to generate HCl gas.

This material has a density of 1.574 g/cm3.

This substance has a melting point of 93.6 °C or 136.5 °F and a boiling point of 76.1 °C or 169.0 °F.

This compound’s vapour pressure is 13.3 kPa.

PCl3 has a dipole moment of 0.97 D.

Utilization of PCl3

This is commonly employed in the production of phosphites.

Additionally, it is utilised to generate a variety of organophosphorus chemicals.

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

PCl3 undergoes oxidation to become POCl3, which has many applications as a plasticizer for PVC and a flame retardant.

PCl3 can also be employed directly in chemical synthesis as a reagent.

Conclusion

Phosphorus trichloride is a chemical compound composed of three chlorine atoms, one phosphorus atom, and a lone pair on the phosphorus atom.

According to the VSEPR theory, the form of PCl3 is tetrahedral, and as chlorine is more electronegative than phosphorus, it attracts the bound electron pair slightly to its side and acquires a partial negative charge, leaving the phosphorus atom with a positive charge.

Polarity is a characteristic of the PCl3 molecule due to its asymmetries and disparities in electronegativity.

If you have any questions regarding the polarity of PCl3, feel free to post them in the comments below. I will contact you as soon as possible.

Read more: Polarity, Lewis Structure, Molecular Geometry, and Hybridization of SO42

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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