Is PCl3 an Ionic or a Covalent Compound?

PCl3 is the chemical formula for phosphorus trichloride, an inorganic molecule. It is a binary compound consisting of two separate elements because it is made up of phosphorus and chlorine.

Is PCl3 an ionic or a covalent compound? Because phosphorus’ high ionisation energy prevents the creation of a P3+ ion, PCl3 is a covalent molecule. To produce a stable electronic state, a covalent link is favoured over an ionic bond. The creation of a covalent bond is likewise favoured by similar Pauling electronegativity values (2.19 and 3.16 for P and Cl, respectively).

PCl3 is made industrially by combining white phosphorus with chlorine.

4PCl3 (P4 + 6Cl2)

It can also react with Cl2 to produce PCl5. As a result, it’s critical to keep the PCl3 product out of the production process at all times.

This is also an application of Le Chatelier’s principle, which asserts that if the product concentration is reduced by external variables, product creation will be preferred.

In its natural state, it is a colourless liquid.

The melting point of PCl3 is -93.6 degrees Celsius (-136.5 degrees Fahrenheit), and the boiling point is 76.1 degrees Celsius (169.0 Fahrenheit).

PCl3 has a low melting point, indicating that it prefers to reside in liquid phases, and a low boiling point, indicating that it is volatile.

We perform a rigorous chemical analysis in this article to establish whether PCl3 is ionic or covalent.

Why is PCl3 a covalent compound?

Let’s look at the electron configuration of P and Cl to see what kind of bonding they have.

P electron configuration: [Ne] 3s2 3p3 (valence electron number = 5)

Cl’s electron configuration is [Ne] 3s2 3p5 (valence electron number = 7)

Assume that the P3+ cation has been produced. We’ll need to remove three electrons from the 3p orbitals to make this viable.

Because of the large electron exchange stabilisation energy, the 3p3 structure is extremely stable. As a result, removing these three electrons to generate the P3+ cation requires a lot of energy.

As a result of the high ionisation energy, the possibility of ionic bonding is ruled out.

The P atom, on the other hand, requires three electrons to complete its octet, whereas the Cl atoms each require one electron to complete their octet.

When electrons are shared between the P and Cl atoms, this is feasible. As a result, each link has one electron from the P atom and one from the Cl atom.

What distinguishes a covalent bind from an ionic bond?

When two atoms share electrons to produce a stable electronic configuration, they form a covalent connection.

The two atoms in question gain and lose electrons to produce a negatively charged anion and a positively charged cation, respectively, in the case of ionic bonding.

The cation and anion acquire stability as a result of having a complete octet, and the cation-anion interaction boosts the molecule’s stability even more.

When the properties of their compounds are compared, the difference between the two can be further elucidated.

Ionic CompoundsCovalent Compounds
Usually crystalline solidsUsually fluids, seldomly solids
High Melting and Boiling Points (Very Strong Bonds)Low Melting and Boiling Points (Weak Bonds)
Soluble in Polar solvents but insoluble in Non-Polar solventsSoluble in Non-Polar solvents but insoluble in Polar solvents
High electrical conductivity in the dissolved or molten stateLow electrical conductivity

The conditions for the development of a covalent bond are as follows:

High Ionization Potential: Because ionisation potential is related to the energy necessary for ion production, both atoms should have a high ionisation potential.

High Electron Affinity: To help share electrons, both atoms should have a high electron affinity.

Electronegativity Difference: The difference in electronegativity should be as little as feasible, because a bigger contrast in electronegativity indicates more ionic nature and less electron sharing.

Using the Lewis structure and the VSEPR Theory, we can bond in PCl3.

To determine the structure of PCl3, we use the following procedure:

Determine the centre atom in step one. We use P as the core atom in our example.

Step 2: Count the valence electrons in the molecule as a whole.

3 x 7 (from 3 Cl) = 26 n1 = 5 (from P) + 3 x 7 (from 3 Cl)

Step 3: Determine how many electrons are required to complete the octet of all atoms.

n2 = 8 x (Atom Count) = 8 x 4 = 32

Step 4: (n2 – n1)/2 = 6/2 = 3 = number of bond pairs

Step 5: Count how many non-bonding electrons there are.

n3 = n1 – (n2 – n1) = 26 – (32 – 26) = 20 n3 = n1 – (n2 – n1) = 26 – (32 – 26) = 20

Step 6: n3/2 = 20/2 = 10 = number of lone pairs

We’re now ready to draw PCl3’s Lewis structure. We start by putting the P atom in the middle and removing three single bonds (3 bond pairs) that connect the Cl atoms.

One of the lone pairs is placed on P to complete its octet, and the other nine lone pairs are uniformly distributed on the Cl atoms to complete their octet.

You can also read the essay I wrote about PCl3’s Lewis structure.

VSEPR theory can be used to predict the molecule’s geometry after knowing the electron distribution in the molecule.

The molecule will adopt a trigonal bipyramidal geometry due to the repulsion between the lone pair on the P atom and the bond pairs on the Cl atoms.

Hybridization Theory for Bonding in PCl3

Take a look at P’s electronic configuration: [Ne] 3s2 3p3

Because the energies of the 3s and 3p orbitals are so near, they can hybridise into four comparable sp3 orbitals.

The lone pair of the P atom will be in one sp3 orbital, while the other three sp3 orbitals will each have one electron.

Each Cl atom’s atomic orbitals can now share electrons with sp3 orbital electrons to complete its octet.

Despite the lack of a fourth bonding atom and the existence of a lone pair, the trigonal bipyramidal geometry is used, with a bond angle of 100 degrees between Cl, P, and Cl (deviates from the ideal 109 degrees because of lone pair repulsion).

PCl3 Characteristics

Chemical Characteristics

PCl3 reacts strongly with water to produce phosphoric acid (H3PO3) and hydrogen chloride (HCl)

PCl3 transforms carboxylic acids to their acid chlorides counterparts.

PCl3 can behave as both a nucleophile and an electrophile (the lone pair on P) (due to vacant d orbitals in P).

The oxidation state of the P atom in PCl3 is +3. Due to the presence of d orbitals in P, several higher oxidation states are feasible.

As a result, PCl3 is easily oxidised to produce additional Phosphorus compounds.

Because Cl- is a good leaving group, PCl3 can undergo substitution processes.

It is poisonous and destructive to biological systems.

Physical Characteristics

PCl3 is an oily, colourless liquid.

Due to its high volatility, it is a fuming liquid.

It has a very strong odour.

PCl3 is denser (1.57 g/cm3) than water (1.00 g/cm3).

Because of the electronegativity difference between P and Cl, PCl3 is slightly polar and thus soluble in slightly polar and organic solvents.

PCl3’s Applications

PCl3 is the raw material used to make compounds such as PCl5, POCl3, and PSCl3. These compounds have economic significance and are used in the manufacture of agricultural chemicals.

It is utilised in organic synthesis as a chlorinating agent and as a catalyst.

It’s used to make detergents and flame retardants, among other things.

  1. PCl3 can be utilised to create coordination compounds, which can be used as catalysts in both organic and inorganic reactions.


Because electrons are exchanged between the P and Cl atoms, PCl3 is a covalent molecule. The P atom is three electrons shy of an octet, while the Cl atoms are only one electron away. Because electrons are shared, all atoms have an inert electron configuration.

The creation of three single bonds between the P and Cl atoms is due to three bond pairs of electrons.

On the P and Cl atoms, the remaining valence electrons appear as non-bonding electrons or lone pairs.

Read more: Molecular Geometry, Hybridization, and Polarity of COCl2 Lewis Structure

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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