PH3 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.

PH3 lewis structure has a Phosphorus atom (P) at the center which is surrounded by three Hydrogen atoms (H). There are 3 single bonds between the Phosphorus atom (P) and each Hydrogen atom (H). There is 1 lone pair on the Phosphorus atom (P).

If you haven’t understood anything from the above image of PH3 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of PH3.

So let’s move to the steps of drawing the lewis structure of PH3.

Steps of drawing PH3 lewis structure

Step 1: Find the total valence electrons in PH3 molecule

In order to find the total valence electrons in PH3 molecule, first of all you should know the valence electrons present in phosphorus atom as well as hydrogen 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 hydrogen using a periodic table.

Total valence electrons in PH3 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 hydrogen atom:

Hydrogen is group 1 element on the periodic table. ^[2] Hence the valence electron present in hydrogen is 1.

You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.

Hence, 

Total valence electrons in PH3 molecule = valence electrons given by 1 phosphorus atom + valence electrons given by 3 hydrogen atoms = 5 + 1(3) = 8.

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.

(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)

Now here the given molecule is PH3 and it contains phosphorus atom (P) and hydrogen atoms (H).

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

If we compare the electronegativity values of phosphorus (P) and hydrogen (H) then the hydrogen atom is less electronegative. But as per the rule we have to keep hydrogen outside.

So here the phosphorus atom (P) is the center atom and the hydrogen atoms (H) are the outside atoms.

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

Now in the PH3 molecule, you have to put the electron pairs between the phosphorus atom (P) and hydrogen atoms (H).

This indicates that the phosphorus (P) and hydrogen (H) are chemically bonded with each other in a PH3 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 PH3 molecule, you can see that the outer atoms are hydrogen atoms.

These outer hydrogen atoms are forming a duplet and hence they are stable. 

Also, in step 1 we have calculated the total number of valence electrons present in the PH3 molecule.

The PH3 molecule has a total 8 valence electrons and out of these, only 6 valence electrons are used in the above sketch.

So the number of electrons which are left = 8 – 6 = 2.

You have to put these 2 electrons on the central phosphorus atom in the above sketch of PH3 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 PH3 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 PH3.

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 hydrogen (H) atoms present in the PH3 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 PH3 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 Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0

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

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

This indicates that the above lewis structure of PH3 is stable and there is no further change in the above structure of PH3.

In the above lewis dot structure of PH3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of PH3.

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:

N2O lewis structure	CH3OH lewis structure
PCl3 lewis structure	BCl3 lewis structure
CF4 lewis structure	XeF2 lewis structure