POCl3 Lewis structure

POCl₃ (phosphoryl chloride) has one phosphorus atom, one oxygen atom, and three chlorine atoms.

In the POCl₃ Lewis structure, there is one double bond and three single bonds around the phosphorus atom, with one oxygen atom and three chlorine atoms attached to it. Each chlorine atom has three lone pairs, and the oxygen atom has two lone pairs.

Alternative method: Lewis structure of POCl₃

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, sulfur lies in group 16, and chlorine lies in group 17.

Hence, phosphorus has five valence electrons, sulfur has six valence electrons, and chlorine has seven valence electrons.

Since POCl₃ has one phosphorus atom, one oxygen atom, and three chlorine atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of one oxygen atom = 6 × 1 = 6
Valence electrons of three chlorine atoms = 7 × 3 = 21

And the total valence electrons = 5 + 6 + 21 = 32

Learn how to find: Phosphorus valence electrons, Oxygen valence electrons, and Chlorine valence electrons

• Second, find the total electron pairs

We have a total of 32 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 32 ÷ 2 = 16

• Third, determine the central atom

We have to place the least electronegative atom at the center.

Since phosphorus is less electronegative than oxygen and chlorine, assume that the central atom is phosphorus.

Therefore, place phosphorus in the center and oxygen and chlorine on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 16 electron pairs. And four bonds are already marked. So we have to only mark the remaining twelve electron pairs as lone pairs on the sketch.

Also remember that both (phosphorus and chlorine) are the period 3 elements, so they can keep more than 8 electrons in their last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygen and chlorines.

So for oxygen and each chlorine, there are three lone pairs, and for phosphorus, there is zero lone pair because all twelve electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For phosphorus atom, formal charge = 5 – 0 – ½ (8) = +1

For oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

For each chlorine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, both phosphorus and oxygen atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both phosphorus and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the oxygen atom to make a new P — O bond with the phosphorus atom as follows:

Final structure

The final structure of POCl₃ contains a central phosphorus atom connected to one oxygen atom and three chlorine atoms. Within this configuration, the phosphorus atom utilizes an expanded valence shell to form a double bond with the oxygen atom and single bonds with each of the three chlorine atoms. This results in the phosphorus atom being surrounded by ten electrons, which minimizes the formal charges across the entire molecule. The oxygen atom fulfills its octet by retaining two lone pairs, while each chlorine atom maintains three lone pairs to reach its stable electronic state. This arrangement is the most stable because it yields a formal charge of zero for every atom. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of phosphorus oxychloride.

Next: SCl₄ Lewis structure

External video

• POCl3 Lewis Structure – How to Draw the Lewis Structure for POCl3 – YouTube • Wayne Breslyn

External links

• https://lambdageeks.com/pocl3-lewis-structure/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/POCl3-lewis-structure.html
• https://geometryofmolecules.com/pocl3-lewis-structure-molecular-geometry-hybridization-bond-angle/
• https://www.chemistryscl.com/general/phosphorus-oxychloride-POCl3-lewis-structure/index.php