PCl3 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.

PCl3 lewis structure has a Phosphorus atom (P) at the center which is surrounded by three Chlorine atoms (Cl). There are 3 single bonds between the Phosphorus atom (P) and each Chlorine atom (Cl). There is 1 lone pair on the Phosphorus atom (P) and 3 lone pairs on all three Chlorine atoms (Cl).

If you haven’t understood anything from the above image of PCl3 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of PCl3.

So let’s move to the steps of drawing the lewis structure of PCl3.

Steps of drawing PCl3 lewis structure

Step 1: Find the total valence electrons in PCl3 molecule

In order to find the total valence electrons in PCl3 molecule, first of all you should know the valence electrons present in phosphorus 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 as well as chlorine using a periodic table.

Total valence electrons in PCl3 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 chlorine atom:

Chlorine is group 17 element on the periodic table. ^[2] 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 PCl3 molecule = valence electrons given by 1 phosphorus atom + valence electrons given by 3 chlorine atoms = 5 + 7(3) = 26.

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 PCl3 (phosphorus trichloride) and it contains phosphorus atom (P) and chlorine atoms (Cl).

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

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

So here the phosphorus atom (P) is the center atom and the chlorine atoms (Cl) are the outside atoms.

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

Now in the PCl3 molecule, you have to put the electron pairs between the phosphorus atom (P) and chlorine atoms (Cl).

This indicates that the phosphorus (P) and chlorine (Cl) are chemically bonded with each other in a PCl3 molecule.

Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.

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

Here in the sketch of PCl3 molecule, you can see that the outer atoms are chlorine atoms.

These outer 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 PCl3 molecule.

The PCl3 molecule has a total 26 valence electrons and out of these, only 24 valence electrons are used in the above sketch.

So the number of electrons which are left = 26 – 24 = 2.

You have to put these 2 electrons on the central phosphorus atom in the above sketch of PCl3 molecule.

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 PCl3 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 PCl3.

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 as well as chlorine (Cl) atoms present in the PCl3 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 PCl3 molecule in the image given below.

For Phosphorus (P) atom:
Valence electrons = 5 (because phosphorus is in group 15)
Bonding electrons = 6
Nonbonding electrons = 2

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

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
P	=	5	–	6/2	–	2	=	0
Cl	=	7	–	2/2	–	6	=	0

From the above calculations of formal charge, you can see that the phosphorus (P) atom as well as chlorine (Cl) atom has a “zero” formal charge.

This indicates that the above lewis structure of PCl3 is stable and there is no further change in the above structure of PCl3.

In the above lewis dot structure of PCl3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of PCl3.

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:

CF4 lewis structure	XeF2 lewis structure
XeF4 lewis structure	PO43- lewis structure
I3- lewis structure	CN- lewis structure