# PH3 Lewis structure

PH3 (phosphine) has one phosphorus atom and three hydrogen atoms.

In the PH3 Lewis structure, there are three single bonds around the phosphorus atom, with three hydrogen atoms attached to it, and on the phosphorus atom, there is one lone pair.

Contents

## Steps

To properly draw the PH3 Lewis structure, follow these steps:

#1 Draw a rough sketch of the structure
#2 Next, indicate lone pairs on the atoms
#3 Indicate formal charges on the atoms, if necessary

Let’s break down each step in more detail.

### #1 Draw a rough sketch of the structure

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, and hydrogen lies in group 1.

Hence, phosphorus has five valence electrons and hydrogen has one valence electron.

Since PH3 has one phosphorus atom and three hydrogen atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of three hydrogen atoms = 1 × 3 = 3

And 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

Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.

Hence, here we have to assume that the central atom is phosphorus.

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

• And finally, draw the rough sketch

### #2 Next, indicate lone pairs on the atoms

Here, we have a total of 4 electron pairs. And three P — H bonds are already marked. So we have to only mark the remaining one electron pair as a lone pair 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 hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for phosphorus, there is one lone pair.

Mark the lone pair on the sketch as follows:

### #3 Indicate formal charges on the atoms, if necessary

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 – 2 – ½ (6) = 0

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

Here, both phosphorus and hydrogen atoms do not have charges, so no need to mark the charges.

In the above structure, you can see that the central atom (phosphorus) forms an octet. And the outside atoms (hydrogens) also form a duet. Hence, the octet rule and duet rule are satisfied.

Therefore, this structure is the stable Lewis structure of PH3.

Next: NO Lewis structure