POCl3 Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

POCl3 lewis structure has a Phosphorus atom (P) at the center which is surrounded by one Oxygen atom (O) and three Chlorine atoms (Cl). There is a double bond between the Phosphorus (P) & Oxygen (O) atom and a single bond between the Phosphorus (P) and Chlorine (Cl) atoms.

If you haven’t understood anything from the above image of POCl3 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of POCl3.

So let’s move to the steps of drawing the lewis structure of POCl3.

Steps of drawing POCl3 lewis structure

Step 1: Find the total valence electrons in POCl3 molecule

In order to find the total valence electrons in a POCl3 molecule, first of all you should know the valence electrons present in phosphorus atom, oxygen atom as well as chlorine atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of phosphorus, oxygen as well as chlorine using a periodic table.

Total valence electrons in POCl3 molecule

→ Valence electrons given by phosphorus atom:

Phosphorus is group 15 element on the periodic table. ^[1] Hence the valence electrons present in phosphorus is 5.

You can see the 5 valence electrons present in the phosphorus atom as shown in the above image.

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. ^[2] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

→ Valence electrons given by chlorine atom:

Chlorine is group 17 element on the periodic table. ^[3] Hence the valence electrons present in chlorine is 7.

You can see the 7 valence electrons present in the chlorine atom as shown in the above image.

Hence, 

Total valence electrons in POCl3 molecule = valence electrons given by 1 phosphorus atom + valence electrons given by 1 oxygen atom + valence electrons given by 3 chlorine atoms = 5 + 6 + 7(3) = 32.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

Now here the given molecule is POCl3 and it contains phosphorus atom (P), oxygen atom (O) and chlorine atoms (Cl).

You can see the electronegativity values of phosphorus atom (P), oxygen atom (O) and chlorine atoms (Cl) in the above periodic table.

If we compare the electronegativity values of phosphorus atom (P), oxygen atom (O) and chlorine atoms (Cl) then the phosphorus atom is less electronegative.

So here the phosphorus atom is the center atom and the oxygen & chlorine atoms are the outside atoms.

Step 3: Connect each atoms by putting an electron pair between them

Now in the POCl3 molecule, you have to put the electron pairs between the phosphorus (P) & oxygen (O) atom and between the phosphorus (P) & chlorine (Cl) atoms.

This indicates that these atoms are chemically bonded with each other in a POCl3 molecule.

Step 4: Make the outer atoms stable

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of POCl3 molecule, you can see that the outer atoms are oxygen atom and chlorine atoms.

These oxygen atom and chlorine atoms are forming an octet and hence they are stable.

Also, in step 1 we have calculated the total number of valence electrons present in the POCl3 molecule.

The POCl3 molecule has a total 32 valence electrons and all these valence electrons are used in the above sketch of POCl3.

Hence there are no remaining electron pairs to be kept on the central atom. 

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom

In this step, you have to check whether the central phosphorus atom (P) is stable or not.

In order to check the stability of the central phosphorus (P) atom, we have to check whether it is forming an octet or not.

You can see from the above picture that the phosphorus atom is forming an octet. That means it has 8 electrons.

And hence the central phosphorus atom is stable.

Now let’s proceed to the final step to check whether the lewis structure of POCl3 is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of POCl3.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on phosphorus (P) atom, oxygen (O) atom as well as chlorine (Cl) atoms present in the POCl3 molecule.

For calculating the formal charge, you have to use the following formula;

Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons

You can see the number of bonding electrons and nonbonding electrons for each atom of POCl3 molecule in the image given below.

For Phosphorus (P) atom:
Valence electrons = 5 (because phosphorus is in group 15)
Bonding electrons = 8
Nonbonding electrons = 0

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6

For Chlorine (Cl) atom:
Valence electron = 7 (because chlorine is in group 17)
Bonding electrons = 2
Nonbonding electrons = 6

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
P	=	5	–	8/2	–	0	=	+1
O	=	6	–	2/2	–	6	=	-1
Cl	=	7	–	2/2	–	6	=	0

From the above calculations of formal charge, you can see that the phosphorus (P) atom has +1 charge and the oxygen (O) atom has -1 charge.

Because of this reason, the above obtained lewis structure of POCl3 is not stable. 

So we have to minimize these charges by shifting the electron pairs towards the phosphorus atom.

After shifting the electron pair from oxygen atom to phosphorus atom, the lewis structure of POCl3 becomes more stable.

In the above lewis dot structure of POCl3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of POCl3.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

HNO2 Lewis Structure	HCO3- Lewis Structure
C3H8 (Propane) Lewis Structure	CH3CN Lewis Structure
SF3- Lewis Structure	CH3Br Lewis Structure