Lewis Structure of PO4 3- (With 5 Simple Steps to Draw!)

Ready to learn how to draw the lewis structure of PO4 3- ion?

Awesome!

Here, I have explained 5 simple steps to draw the lewis dot structure of PO4 3- ion (along with images).

So, if you are ready to go with these 5 simple steps, then let’s dive right into it!

Lewis structure of PO43- ion (phosphate ion) contains one double bond and three single bonds between the Phosphorus (P) atom and Oxygen (O) atoms. The Phosphorus atom (P) is at the center and it is surrounded by 4 Oxygen atoms (O). 

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 PO4^3- ion).

5 Steps to Draw the Lewis Structure of PO43-

Step #1: Calculate the total number of valence electrons

Here, the given ion is PO4^3-. In order to draw the lewis structure of PO4^3- ion, first of all you have to find the total number of valence electrons present in the PO4^3- ion.
(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 PO4 3- ion

• 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).

Hence in a PO43- ion, 

Valence electrons given by Phosphorus (P) atom = 5
Valence electrons given by each Oxygen (O) atom = 6
Electron due to -3 charge, 3 more electron is added
So, total number of Valence electrons in PO4^3- ion = 5 + 6(4) + 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). ^[3]

Here in the PO4^3- ion, if we compare the phosphorus atom (P) and oxygen atom (O), then phosphorus is less electronegative than oxygen.

So, phosphorus should be placed in the center and the remaining 4 oxygen atoms will surround it.

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

Now in the above sketch of PO4, put the two electrons (i.e electron pair) between each phosphorus atom and oxygen atom to represent a chemical bond between them.

These pairs of electrons present between the Phosphorus (P) and Oxygen (O) atoms form a chemical bond, which bonds the phosphorus and oxygen atoms with each other in a PO4^3- ion.

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 PO4^3- ion, the outer atoms are oxygen atoms.

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

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

Also, all the 32 valence electrons of PO4^3- ion (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 PO4^3- ion.

Let’s move to the next step.

Step #5: Check the formal charge

You can see from the above image that the central atom (i.e phosphorus), is having 8 electrons. So it fulfills the octet rule.

But, in order to get the most stable lewis structure, we have to check the formal charge on PO4^3- ion.

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

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

Let’s keep these charges on the atoms in the above lewis structure of PO4^3- ion.

As we know that phosphorus can hold more than 8 electrons, we can further reduce the charges as mentioned below.

By doing this, the formal charges on the left oxygen as well as phosphorus becomes “zero”, and this gives us the most stable lewis structure of PO4^3-.

There are three -ve charges left on the oxygen atom, which indicates the 3- formal charge on the PO4^3- ion.

Each electron pair (:) in the lewis dot structure of PO4^3- ion represents the single bond ( | ). So the above lewis dot structure of PO4^3- ion can also be represented as shown below.

Related lewis structures for your practice:
Lewis structure of I3-
Lewis structure of CN-
Lewis structure of PF3
Lewis structure of PCl5
Lewis structure of H2O2

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