PO4 3- Lewis Structure in 5 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

PO4 3- (phosphate ion) lewis structure has a Phosphorus atom (P) at the center which is surrounded by four Oxygen atoms (O). There is 1 double bond and 3 single bonds between the Phosphorus atom (P) and each Oxygen atom (O). There are 2 lone pairs on double bonded Oxygen atom (O) and 3 lone pairs on single bonded Oxygen atom (O).

If you haven’t understood anything from the above image of PO4 3- lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of PO4^3- ion.

So let’s move to the steps of drawing the lewis structure of PO4^3- ion.

Steps of drawing PO4 3- lewis structure

Step 1: Find the total valence electrons in PO4 3- ion

In order to find the total valence electrons in PO4 3- ion (phosphate ion), first of all you should know the valence electrons present in phosphorus atom as well as oxygen 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 oxygen using a periodic table.

Total valence electrons in PO4 3- ion

→ 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 oxygen atom:

Oxygen is group 16 element on the periodic table. ^[2] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

Hence, 

Total valence electrons in PO4^3- ion = valence electrons given by 1 phosphorus atom + valence electrons given by 4 oxygen atoms + 3 more electrons are added due to 3 negative charges = 5 + 6(4) + 3 = 32.

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 ion is PO4 3- ion and it contains phosphorus atom (P) and oxygen atoms (O).

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

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

So here the phosphorus atom (P) is the center atom and the oxygen atoms (O) are the outside atoms.

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

Now in the PO4 molecule, you have to put the electron pairs between the phosphorus atom (P) and oxygen atoms (O).

This indicates that the phosphorus (P) and oxygen (O) are chemically bonded with each other in a PO4 molecule.

Step 4: Make the outer atoms stable

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

Here in the sketch of PO4 molecule, you can see that the outer atoms are oxygen atoms.

These outer oxygen 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 PO4^3- ion.

The PO4^3- ion has a total 32 valence electrons and all these valence electrons are used in the above sketch.

Hence there are no remaining electron pairs to be kept on the central atom. 

So now let’s proceed to the next step.

Step 5: 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 PO4^3- ion.

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 oxygen (O) atoms present in the PO4 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 PO4 molecule in the image given below.

For Phosphorus (P) atom:
Valence electrons = 5 (because phosphorus is in group 15)
Bonding electrons = 8
Nonbonding electrons = 0

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6

From the above calculations of formal charge, you can see that the phosphorus (P) atom has +1 charge while the oxygen atom has -1 charge.

So let’s keep these charges on the respective atoms of the PO4 molecule.

The above image shows that the lewis structure of PO4 is not stable.

So we have to minimize these charges by shifting the electron pair from the oxygen atom to the phosphorus atom.

After shifting the electron pair from the oxygen atom to the phosphorus atom, the charges on phosphorus and one oxygen atom becomes zero. And this is a more stable lewis structure. (see below image).

There are three -ve charges left on the oxygen atoms, which gives -3 formal charge on the PO4 molecule.

This overall -3 charge on the PO4 molecule is represented in the image given below.

In the above lewis dot structure of PO4 3- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of PO4 3- ion.

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:

About author

Jay Rana

Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.

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