POCl3 Lewis Structure

POCl3 Lewis Structure

POCl3 (phosphoryl chloride) has one phosphorus atom, one oxygen atom, and three chlorine atoms. In the lewis structure of POCl3, 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.


Here’s how you can draw the POCl3 lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)

Let’s break down each step in detail.

#1 Draw 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

  • 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
POCl3 Lewis Structure (Step 1)

#2 Mark Lone Pairs

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:

POCl3 Lewis Structure (Step 2)

#3 Mark Charges

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:

POCl3 Lewis Structure (Step 3)

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.

#4 Minimize Charges

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

POCl3 Lewis Structure (Step 4)

In the above structure, you can see that the central atom (phosphorus) forms an octet. Hence, the octet rule is satisfied.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of POCl3.

Next: SCl4 Lewis Structure

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