PBr5 (phosphorus pentabromide) has one phosphorus atom and five bromine atoms. In the lewis structure of PBr5, there are five single bonds around the phosphorus atom, with five bromine atoms attached to it, and on each bromine atom, there are three lone pairs.
Here’s how you can draw the PBr5 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
Hence, phosphorus has five valence electrons and bromine has seven valence electrons.
Since PBr5 has one phosphorus atom and five bromine atoms, so…
Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of five bromine atoms = 7 × 5 = 35
And the total valence electrons = 5 + 35 = 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 bromine, assume that the central atom is phosphorus.
Therefore, place phosphorus in the center and bromines on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 20 electron pairs. And five P — Br bonds are already marked. So we have to only mark the remaining fifteen electron pairs as lone pairs on the sketch.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are bromines.
So for each bromine, there are three lone pairs, and for phosphorus, there is zero lone pair because all fifteen 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 phosphorus atom, formal charge = 5 – 0 – ½ (10) = 0
For each bromine atom, formal charge = 7 – 6 – ½ (2) = 0
Here, both phosphorus and bromine atoms do not have charges, so no need to mark the charges.
And in the above structure, you can see that the central atom (phosphorus) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the stable lewis structure of PBr5.
Next: SO42- Lewis Structure