Lewis Structure of PH3 (With 6 Simple Steps to Draw!)

I’m super excited to teach you the lewis structure of PH3 in just 6 simple steps.

Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of PH3 molecule.

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

Lewis structure of PH3 contains three single bonds between the Phosphorus (P) atom and each Hydrogen (H) atom. The Phosphorus atom (P) is at the center and it is surrounded by 3 Hydrogen atoms (H). The Phosphorus atom has one lone pair.

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 PH3).

6 Steps to Draw the Lewis Structure of PH3

Step #1: Calculate the total number of valence electrons

Here, the given molecule is PH3. In order to draw the lewis structure of PH3, first of all you have to find the total number of valence electrons present in the PH3 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 PH3

• 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 Hydrogen: 

Hydrogen is a group 1 element on the periodic table. ^[2]

Hence, the valence electron present in hydrogen is 1 (see below image).

Hence in a PH3 molecule, 

Valence electrons given by Phosphorus (P) atom = 5
Valence electron given by each Hydrogen (H) atom = 1
So, total number of Valence electrons in PH3 molecule = 5 + 1(3) = 8

Step #2: Select the center atom (H is always outside)

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). ^[3]

Here in the PH3 molecule, if we compare the phosphorus atom (P) and hydrogen atom (H), then hydrogen is less electronegative than phosphorus. But as per the rule, we have to keep hydrogen outside.

So, phosphorus should be placed in the center and the remaining 3 hydrogen atoms will surround it.

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

Now in the above sketch of PH3 molecule, put the two electrons (i.e electron pair) between each phosphorus atom and hydrogen atom to represent a chemical bond between them.

These pairs of electrons present between the Phosphorus (P) and Hydrogen (H) atoms form a chemical bond, which bonds the phosphorus and hydrogen atoms with each other in a PH3 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 PH3, the outer atoms are hydrogen atoms.

So now, you have to check whether these hydrogen atoms are forming a duplet or not! (because hydrogen requires only 2 electrons to have a complete outer shell).

You can see in the above image that all the hydrogen atoms form a duplet.

Also, only 6 valence electrons of PH3 molecule are used in the above structure.

But there are total 8 valence electrons in PH3 molecule (as calculated in step #1).

So the number of electrons left to be kept on the central atom = 8 – 6 = 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 has 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 hydrogen atom (H).

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 Hydrogen:
  Valence electron = 1 (as it is in group 1)
  Nonbonding electrons = 0
  Bonding electrons = 2

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
P	=	5	–	2	–	6/2	=	0
H	=	1	–	0	–	2/2	=	0

So you can see above that the formal charges on phosphorus as well as hydrogen are “zero”.

Hence, there will not be any change in the above structure and the above lewis structure of PH3 is the final stable structure only.

Each electron pair (:) in the lewis dot structure of PH3 represents the single bond ( | ). So the above lewis dot structure of PH3 can also be represented as shown below.

Related lewis structures for your practice:
Lewis structure of NO
Lewis structure of N2O
Lewis structure of CH3OH
Lewis structure of PCl3
Lewis structure of BCl3

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