PBr3 Lewis structure

PBr₃ (phosphorus tribromide) has one phosphorus atom and three bromine atoms.

In the PBr₃ Lewis structure, there are three single bonds around the phosphorus atom, with three bromine atoms attached to it. Each bromine atom has three lone pairs, and the phosphorus atom has one lone pair.

Alternative method: Lewis structure of PBr₃

Rough sketch

• First, determine the total number of valence electrons

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

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

Since PBr₃ has one phosphorus atom and three bromine atoms, so…

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

And the total valence electrons = 5 + 21 = 26

Learn how to find: Phosphorus valence electrons and Bromine valence electrons

• Second, find the total electron pairs

We have a total of 26 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 = 26 ÷ 2 = 13

• 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

Lone pair

Here, we have a total of 13 electron pairs. And three P — Br bonds are already marked. So we have to only mark the remaining ten 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 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 bromines.

So for each bromine, there are three lone pairs, and for phosphorus, there is one lone pair.

Mark the lone pairs on the sketch as follows:

Formal charge

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 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.

Final structure

The final structure of PBr₃ features a central phosphorus atom linked to three bromine atoms through single covalent bonds. Within this configuration, the phosphorus atom completes its octet by sharing three valence electrons and retaining one lone pair, while each bromine atom satisfies its octet with three lone pairs of its own. This arrangement results in formal charges of zero for all participating atoms, ensuring the molecule exists in its most stable and energetically favorable state. Consequently, this specific electron distribution represents the definitive and most accurate Lewis representation of phosphorus tribromide.

Next: CH₃Br Lewis structure

External video

• PBr3 Lewis Structure – How to Draw the Lewis Structure for PBr3 – YouTube • Wayne Breslyn

External links

• https://geometryofmolecules.com/pbr3-lewis-structure-molecular-geometry-hybridization-polarity/
• https://techiescientist.com/pbr3-lewis-structure/
• https://topblogtenz.com/pbr3-lewis-structure-molecular-geometry-bond-angle-polar-or-non-polar/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/PBr3-lewis-structure.html
• https://lambdageeks.com/pbr3-lewis-structure/
• https://sciedutut.com/pbr3-lewis-structure/