POBr3 Lewis structure

POBr3 (phosphoryl bromide) has one phosphorus atom, one oxygen atom, and three bromine atoms.

In POBr3 Lewis structure, there is one double bond and three single bonds around the phosphorus atom, with one oxygen atom and three bromine atoms attached to it. The oxygen atom has two lone pairs, and each bromine atom has three lone pairs.

Contents

Steps

Use these steps to correctly draw the POBr3 Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required
#4 Convert lone pairs of the atoms, and minimize formal charges
#5 Repeat step 4 if needed, until all charges are minimized, to get a stable Lewis structure

Let’s discuss each step in more detail.

#1 First draw a rough sketch

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, oxygen lies in group 16, and bromine lies in group 17.

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

Since POBr3 has one phosphorus atom, one oxygen atom, and three bromine atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of one oxygen atom = 6 × 1 = 6
Valence electrons of three bromine atoms = 7 × 3 = 21

And the total valence electrons = 5 + 6 + 21 = 32

• Second, find the total electron pairs

We have a total of 32 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 = 32 ÷ 2 = 16

• Third, determine the central atom

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

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

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

• And finally, draw the rough sketch

#2 Mark lone pairs on the atoms

Here, we have a total of 16 electron pairs. And four bonds are already marked. So we have to only mark the remaining twelve 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. Oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell. And bromine is a period 4 element, so it can keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygen and bromines.

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

Mark the lone pairs on the sketch as follows:

#3 Calculate and mark formal charges on the atoms, if required

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 (8) = +1

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

For each bromine atom, formal charge = 7 – 6 – ½ (2) = 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 Convert lone pairs of the atoms, and minimize formal charges

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. And the outside atoms (oxygen and bromines) also form 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 POBr3.

Next: PH2 Lewis structure