I’m super excited to teach you the lewis structure of PCl3 in just 6 simple steps.
Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of PCl3 molecule.
So, if you are ready to go with these 6 simple steps, then let’s dive right into it!
Lewis structure of PCl3 contains three single bonds between the Phosphorus (P) atom and each Chlorine (Cl) atom. The Phosphorus atom (P) is at the center and it is surrounded by 3 Chlorine atoms (Cl). The Phosphorus atom has 1 lone pair and all the three Chlorine atoms have 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 PCl3).
6 Steps to Draw the Lewis Structure of PCl3
Step #1: Calculate the total number of valence electrons
Here, the given molecule is PCl3 (phosphorus trichloride). In order to draw the lewis structure of PCl3, first of all you have to find the total number of valence electrons present in the PCl3 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 PCl3
- For Phosphorus:
Phosphorus is a group 15 element on the periodic table.
Hence, the valence electrons present in phosphorus is 5 (see below image).
- For Chlorine:
Chlorine is a group 17 element on the periodic table.
Hence, the valence electron present in chlorine is 7 (see below image).
Hence in a PCl3 molecule,
Valence electrons given by Phosphorus (P) atom = 5
Valence electrons given by each Chlorine (Cl) atom = 7
So, total number of Valence electrons in PCl3 molecule = 5 + 7(3) = 26
Step #2: Select the center atom
While selecting the 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).
Here in the PCl3 molecule, if we compare the phosphorus atom (P) and chlorine atom (Cl), then the phosphorus is less electronegative than chlorine.
So, phosphorus should be placed in the center and the remaining 3 chlorine atoms will surround it.
Step #3: Put two electrons between the atoms to represent a chemical bond
Now in the above sketch of PCl3 molecule, put the two electrons (i.e electron pair) between each phosphorus atom and chlorine atom to represent a chemical bond between them.
These pairs of electrons present between the Phosphorus (P) and Chlorine (Cl) atoms form a chemical bond, which bonds the phosphorus and chlorine atoms with each other in a PCl3 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 PCl3, the outer atoms are chlorine atoms.
So now, you have to complete the octet on these chlorine atoms (because chlorine requires 8 electrons to have a complete outer shell).
Now, you can see in the above image that all the chlorine atoms form an octet.
Also, only 24 valence electrons of PCl3 molecule are used in the above structure.
But there are total 26 valence electrons in PCl3 molecule (as calculated in step #1).
So the number of electrons left to be kept on the central atom = 26 – 24 = 2.
So let’s keep these two electrons (i.e electron pair) on the central atom.
Now, 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 and the phosphorus atom is stable.
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) 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 = 2
Bonding electrons = 6
- 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|
So you can see above that the formal charges on phosphorus as well as chlorine are “zero”.
Hence, there will not be any change in the above structure and the above lewis structure of PCl3 is the final stable structure only.
Each electron pair (:) in the lewis dot structure of PCl3 represents the single bond ( | ). So the above lewis dot structure of PCl3 can also be represented as shown below.