# P2O5 Lewis Structure

P2O5 (phosphorus pentoxide) has two phosphorus atoms and five oxygen atoms. In the lewis structure of P2O5, there are two single bonds around the center oxygen atom, with two phosphorus atoms attached to it, and each phosphorus makes two double bonds with other two oxygen atoms. And on each oxygen atom, there are two lone pairs.

## Steps

Here’s how you can draw the P2O5 lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)

Let’s break down each step in detail.

### #1 Draw Sketch

• 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 P2O5 has two phosphorus atoms and five oxygen atoms, so…

Valence electrons of two phosphorus atoms = 5 × 2 = 10
Valence electrons of five oxygen atoms = 6 × 5 = 30

And the total valence electrons = 10 + 30 = 40

• Second, find the total electron pairs

We have a total of 40 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 = 40 ÷ 2 = 20

• 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.

Here, there are two phosphorus atoms, so we can assume any one as the central atom.

Let’s assume that the central atom is left phosphorus.

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

• And finally, draw the rough sketch

### #2 Mark Lone Pairs

Here, we have a total of 20 electron pairs. And six bonds are already marked. So we have to only mark the remaining fourteen 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 and right phosphorus.

So for each top oxygen, left oxygen, and right oxygen, there are three lone pairs. For center oxygen, there are two lone pairs, and for phosphorus, there is zero lone pair because all fourteen electron pairs are over.

Mark the lone pairs on the sketch as follows:

### #3 Mark Charges

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

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

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

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

For center oxygen atom, formal charge = 6 – 4 – ½ (4) = 0

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 Charges

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

### #5 Minimize Charges Again

Since there are charges on phosphorus and oxygen atoms, again convert a lone pair of the top oxygen atom to make a new P — O bond with the left phosphorus atom as follows:

### #6 Minimize Charges Again

There are still charges on phosphorus and oxygen atoms, so again convert a lone pair of the right oxygen atom to make a new P — O bond with the right phosphorus atom as follows:

### #7 Minimize Charges Again

There are still charges on phosphorus and oxygen atoms, so again convert a lone pair of the top oxygen atom to make a new P — O bond with the right phosphorus atom as follows:

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

Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of P2O5.