Lewis Structure of POCl3 (With 6 Simple Steps to Draw!)

I’m super excited to teach you the lewis structure of POCl3 in just 6 simple steps.

Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of POCl3 molecule.

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of POCl3 contains 1 double bond between the Phosphorus (P) & Oxygen (O) atom and 3 single bonds between the Phosphorus (P) atom & each Chlorine (Cl) atom. The Phosphorus atom (P) is at the center and it is surrounded by 1 Oxygen atom (O) and 3 Chlorine atoms (Cl). The Oxygen atom (O) has 2 lone pairs while the Chlorine atom (Cl) has 3 lone pairs.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of POCl3).

6 Steps to Draw the Lewis Structure of POCl3

Step #1: Calculate the total number of valence electrons

Here, the given molecule is POCl3. In order to draw the lewis structure of POCl3, first of all you have to find the total number of valence electrons present in the POCl3 molecule.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in POCl3

For Phosphorus:

Phosphorus is a group 15 element on the periodic table. ^[1]

Hence, the valence electrons present in phosphorus is 5 (see below image).

For Oxygen:

Oxygen is a group 16 element on the periodic table. ^[2]

Hence, the valence electron present in oxygen is 6 (see below image).

For Chlorine:

Chlorine is a group 17 element on the periodic table. ^[3]

Hence, the valence electron present in chlorine is 7 (see below image).

Hence in a POCl3 molecule,

Valence electrons given by Phosphorus (P) atom = 5
Valence electrons given by Oxygen (O) atom = 6
Valence electrons given by each Chlorine (Cl) atom = 7
So, total number of Valence electrons in POCl3 molecule = 5 + 6 + 7(3) = 32

Step #2: Select the center atom

While selecting the center atom, always put the least electronegative atom at the center.

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[4]

Here in the POCl3 molecule, if we compare the phosphorus atom (P), oxygen atom (O) and chlorine atom (Cl), then phosphorus is less electronegative than chlorine and oxygen.

So, phosphorus should be placed in the center and the remaining 3 chlorine atoms and 1 oxygen atom will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of POCl3 molecule, put the two electrons (i.e electron pair) between the phosphorus atom, oxygen atom and chlorine atom to represent a chemical bond between them.

These pairs of electrons present between the Phosphorus (P), Oxygen (O) and Chlorine (Cl) atoms form a chemical bond, which bonds these atoms with each other in a POCl3 molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of POCl3, the outer atoms are oxygen atom and chlorine atoms.

So now, you have to complete the octet on these oxygen and chlorine atoms (because oxygen and chlorine requires 8 electrons to have a complete outer shell).

Now, you can see in the above image that the oxygen and chlorine atoms form an octet.

Also, all the 32 valence electrons of POCl3 molecule (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of POCl3.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e phosphorus) has an octet or not.

In simple words, we have to check whether the central Phosphorus (P) atom is having 8 electrons or not.

As you can see from the above image, the central atom (i.e phosphorus), has 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on phosphorus atom (P), oxygen atom (O) as well as each chlorine atom (Cl).

For that, you need to remember the formula of formal charge;

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

For Phosphorus:
Valence electrons = 5 (as it is in group 15)
Nonbonding electrons = 0
Bonding electrons = 8
For Oxygen:
Valence electron = 6 (as it is in group 16)
Nonbonding electrons = 6
Bonding electrons = 2
For Chlorine:
Valence electron = 7 (as it is in group 17)
Nonbonding electrons = 6
Bonding electrons = 2

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

So you can see above that the formal charges on phosphorus is +1 and the formal charge on the oxygen atom is -1.

This indicates that the above lewis structure of POCl3 is not stable and so we have to minimize the charges to get a more stable lewis structure.

This can be done by shifting the lone pair from negatively charged oxygen atom to the positively charged phosphorus atom to form a double bond.

Now, in the above structure, you can see that the charges are minimized and the above lewis structure of POCl3 is the final stable structure.

Each electron pair (:) in the lewis dot structure of POCl3 represents the single bond ( | ). So the above lewis dot structure of POCl3 can also be represented as shown below.

Article by;

Jay Rana

Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. With a desire to make learning accessible for everyone, he founded Knords Learning, an online learning platform that provides students with easily understandable explanations. Read more about our Editorial process.

Author