PO3- Lewis structure

PO3 has one phosphorus atom and three oxygen atoms.

In PO3 Lewis structure, there is one double bond and two single bonds around the phosphorus atom, with three oxygen atoms attached to it. The oxygen atom with a double bond has two lone pairs, and the two oxygen atoms with single bonds have three lone pairs.

Also, there is a negative (-1) charge on the two oxygen atoms with single bonds, and a positive (+1) charge on the phosphorus atom.

Contents

Steps

Here’s how you can easily draw the PO3 Lewis structure step by step:

#1 Draw a rough skeleton structure
#2 Mention lone pairs on the atoms
#3 If needed, mention formal charges on the atoms
#4 Minimize formal charges by converting lone pairs of the atoms, and try to get a stable Lewis structure
#5 Repeat step 4 again if needed, until all charges are minimized

Now, let’s take a closer look at each step mentioned above.

#1 Draw a rough skeleton structure

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, and oxygen lies in group 16.

Hence, phosphorus has five valence electrons and oxygen has six valence electrons.

Since PO3 has one phosphorus atom and three oxygen atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of three oxygen atoms = 6 × 3 = 18

Now the PO3 has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 5 + 18 + 1 = 24

• Second, find the total electron pairs

We have a total of 24 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 24 ÷ 2 = 12

• Third, determine the central atom

We have to place the least electronegative atom at the center.

Since phosphorus is less electronegative than oxygen, assume that the central atom is phosphorus.

Therefore, place phosphorus in the center and oxygens on either side.

• And finally, draw the rough sketch

#2 Mention lone pairs on the atoms

Here, we have a total of 12 electron pairs. And three P — O bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that phosphorus is a period 3 element, so it can keep more than 8 electrons in its last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygens.

So for each oxygen, there are three lone pairs, and for phosphorus, there is zero lone pair because all nine electron pairs are over.

Mark the lone pairs on the sketch as follows:

#3 If needed, mention formal charges on the atoms

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For phosphorus atom, formal charge = 5 – 0 – ½ (6) = +2

For each oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

Here, both phosphorus and oxygen atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both phosphorus and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

#4 Minimize formal charges by converting lone pairs of the atoms

Convert a lone pair of the oxygen atom to make a new P — O bond with the phosphorus atom as follows:

In the above structure, you can see that the central atom (phosphorus) forms an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the two oxygen atoms, and a positive (+1) charge on the phosphorus atom.

This is okay, because the structure with a negative charge on the most electronegative atom is the best Lewis structure. And in this case, the most electronegative element is oxygen.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the most stable Lewis structure of PO3.

And since the PO3 has a negative (-1) charge, mention that charge on the Lewis structure by drawing brackets as follows:

FAQs

How many valence electrons are in PO3– ion?

We can calculate the total number of valence electrons for PO3 by adding up the valence electrons of each atom in the ion.

Phosphorus, which is in group 5 of the periodic table, has five valence electrons. And each oxygen atom has six valence electrons. Also, PO3 has a negative (-1) charge, so we have to add one more electron.

Therefore, the PO3 ion has a total of 5 + 6(3) + 1 = 24 valence electrons.

What’s the formal charge on each atom in PO3– ion?

The PO3 ion has one phosphorus atom and three oxygen atoms. The central atom (phosphorus) has a formal charge of +1. One oxygen atom with a double bond has a formal charge of 0, and the remaining two oxygen atoms with single bonds have -1 formal charge.

Does PO3– satisfy the octet rule for all atoms?

The most stable Lewis structure of PO3 ion contains phosphorus, the central atom that makes one double bond and two single bonds with the surrounding three oxygen atoms, forming an octet. And each oxygen atom also has eight electrons in its outer shell resulting in a full octet.

Therefore, the PO3 satisfies the octet rule for all atoms.