# P3- Lewis Structure

P3- (phosphide) has one phosphorus atom. In the lewis structure of P3-, there are four lone pairs on the phosphorus atom.

Also, there is a negative (-3) charge on the phosphorus atom.

## Steps

Here’s how you can draw the P3- lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges (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. Hence, phosphorus has five valence electrons.

Since P3- has one phosphorus atom, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5

Now the P3- has a negative (-3) charge, so we have to add three more electrons.

So the total valence electrons = 5 + 3 = 8

• Second, find the total electron pairs

We have a total of 8 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 = 8 ÷ 2 = 4

• Third, determine the central atom

There is only one atom present here, so assume that the central atom is phosphorus.

• And finally, draw the rough sketch

### #2 Mark Lone Pairs

Here, we have a total of 4 electron pairs. So we have to mark these four 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.

Always start to mark the lone pairs from outside atoms. But here, there is no outside atom. So for phosphorus, there are four lone pairs.

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 phosphorus atom, formal charge = 5 – 8 – ½ (0) = -3

Here, the phosphorus atom has a charge, so mark it on the sketch 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 (-3) 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 phosphorus.

Therefore, this structure is the most stable lewis structure of P3-.

And since the P3- has a negative (-3) charge, mention that charge on the lewis structure by drawing brackets as follows: