Molecular Geometry, Polarity, and Hybridization of PBr3 Lewis Structure

PBr3 is a colourless fuming chemical compound with a pungent odour that is liquid at room temperature.

It has the unusual property of behaving as a Lewis acid and a Lewis base at the same time.

The following is how PBr3 is made:

2P     +    3Br3    ——>    2PBr3

It has a boiling point of 1750 degrees Celsius and a freezing point of 400 degrees Celsius.

It has a variety of uses. It can be used as a fire extinguisher, in the making of medications, as catalysts, and for sugar analysis.

However, it can irritate the respiratory tract and other internal organs of the human body, causing significant skin damage.

Aside from that, it is extremely poisonous and has the potential to produce explosions.

Because phosphorus tribromide plays such a crucial part in the bromination of acids and the conversion of alcohols, it’s critical that we learn everything we can about it.

An thorough article on the chemical bonding of PBr3 has been published.

Lewis Structure of PBr3

Before we begin explaining the Lewis Structure of PBr3, we should have a basic understanding of the concept and why we need to learn it.

Introduction and Definition

Lewis Structure is a method for determining the kind and position of atoms in a molecule for the purpose of chemical bonding.

This term was coined by Gilbert N Lewis and refers to a diagrammatic representation of a chemical molecule’s bonds and valence electrons.

Here, we’ll try to draw a skeleton diagram of the molecule using symbols for atoms, dots for valence electrons, and straight lines for bonds.

For every given ion or molecule, this is a two-dimensional approach and hence one of the first and most important phases in chemical bonding.

A phosphorus atom and three bromine atoms make up the chemical Phosphorus tribromide, or Pbr3. Phosphorus has a valency of 5 due to its atomic number of 15.

Br is a halogen with seven valence electrons that belongs to the family of halogens.

The total number of valence electrons in a single PBr3 molecule is 5 + 7*3.

5 + 21 =

equals 26

We must now identify the core atom after calculating the valence electron number ( the atom with the least electronegativity value).

Because phosphorus is less electronegative, it will behave as the centre atom, surrounded by three bromine atoms.

So, here is how we’ve arranged the four atoms within the molecule.

We’ll now use dots to represent the outermost shell electrons around each atom so we can check the bond formation and lone pairs.

We’ll use the octet rule in this case.

We strive to establish the tendency of every main group atomic element to attain its octet electronic configuration according to the periodic table using the octet rule.

Every atom, including the core P and the surrounding Br, has attained octet completion, as can be seen.

Although this is considered the best Lewis structure for PBr3, we can never be certain.

We’ll stick to the formal charge rule from now on to ensure that all of the constituent atoms are present at their lowest formal charge values.

This is how the formal charge is calculated.

The formal charge for P is 5 – 0.5*6 – 2 = 0.

The formal charge for Br is 7 – 0.5*2 – 6 = 0 (this holds true for all three bromine atoms). Now we need to add the single bonds to complete our Lewis Structure.

Molecular Geometry of PBr3

Our next idea is Molecular Bonding, which we learn about by studying the Lewis structure.

Introduction and Definition

The entire cosmos, including our planet, is made up of millions and billions of atoms that combine to produce a variety of chemical structures that lead to new compounds. Each of these molecules within a compound has a distinct shape that can be better characterised in three dimensions.

Lewis Structure has its own set of limitations; for example, it cannot assist us in determining the 3D structure of any molecule. So, the VSEPR hypothesis, or Valence Shell Electron Pair Repulsion Model theory, comes into play.

In chemical bonding, the VSEPR theory is critical for understanding a molecule’s molecular geometry, as well as its bond angles and lengths.

Electrons, which are most likely negatively charged, form a cloud above the nuclei, causing them to reject each other in order to preserve equilibrium. This repulsion is reduced to produce a stable molecule, which allows it to achieve its desired shape.

The VSEPR theory was used to calculate the molecular structure of PBr3.

In the instance of Phosphorous Tribromide, we need to use the VSEPR model to figure out the molecular geometry.

The notation AXN is used in the VSEPR theory. The centre atom, Phosphorous, is represented by the letter A. Three bromine atoms circle the centre P, denoted by the letter X.

And N refers to the centre P’s lone pair of electrons.

As a result, it’s AX3N.

Take a look at the diagram above.

There are four electron-dense places in PBr3, three of which are bound zones and one of which is a lone pair around the core atom.

As a result, a trigonal bipyramidal shape is required. The bond angle is around 109.5 degrees.

Polarity of PBr3

Let’s take a look at a hot issue right now: polarity.

Introduction and Definition

The polarity of a molecule can be determined by drawing the electron dot structure and establishing the 3D geometry of a specific molecule.

What exactly is polarity? Why is it important to know if a molecule is polar or nonpolar?

We need to introduce another concept called dipole moment to explain the term polarity.

Do you know that when atoms come together to build a structure, bonds are formed, which can occasionally be between elements with different electronegativity values?

This causes a separation of electric charges as well as the presence of partial positive and negative poles, resulting in polarity and the production of a dipole moment.

We acquire a net-zero dipole when there is no electric charge separation, i.e. there is no difference in electronegativity or the charges cancel out each other inside a molecule, and the molecules are called non-polar.

Is PBr3 a polar or nonpolar substance?

PBr3 has one P atom with an electronegativity of 2.19 and three Br atoms with an electronegativity of 2.96 apiece. Because of the large difference, we have polar bonds between P and Br, in which each bond has a + partial charge near P and a – partial charge near Br.

Is it possible to achieve a net-zero dipole moment by cancelling the bonds?

The answer is a resounding no.

We’ve already discovered that PBr3 has a trigonal bipyramidal geometry that is asymmetrical. As a result, the dipole moments do not cancel out, and we end up with a polar molecule.

I’ve also prepared a full post about PBr3’s polarity.

Hybridization of PBr3

Hybridization is a key concept in chemical bonding, and it is based on mathematical probability functions known as atomic orbitals in a specific x-y-z plane.

The idea of hybridization was proposed by Linus Pauling, a well-known chemist. We operate with many orbitals such as s,p,d,f, and so on.

Hybridized orbitals, such as sp, sp2, sp3, sp3d, and so on, are formed by mixing these orbitals.

Quantum mechanics explains this by describing the superimposition of many AOs with comparable energy with variable amounts.

What is the PBr3 hybridization?

Let’s look at what we already know about the bonding nature of a phosphorus tribromide molecule before we go into the hybridization type.

The most suited Lewis Structure was discovered, and the single bonds produced between P and each Br atom were examined. (Br-P-P-P-P-P-P-P-P

We discovered that PBr3 is polar and has a trigonal bipyramidal shape due to its asymmetrical feature.

When it comes to electronic setups,

In the case of phosphorus,

1s2 2s2 2p6 3s2 3p3 P:1s2 2s2 2p6 3s2 3p3

When it comes to bromine,

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 Br:1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

Due to the three single bonding between P and Br in PBr3, a total of three sigma bonds are created. On the centre atom P, there is a single lone pair.

As a result, a tetrahedral structure occurs, resulting in sp3 hybridization. With three bond pairs and one lone pair, the phosphorus atom forms the sp3 hybridization. One’s’ electron is energised and moves to the d orbital.

As a result, sp3 is formed when the one 3s electron and the other three electrons in 3p orbitals unite.


In this post, we looked at one of the most well-known phosphorus halides in depth. We learned about the Lewis Structure, hybridization, molecular geometry, and polarity of PBr3, or phosphorous tribromide, which is a significant molecular composition.

Good luck with your studies!

Read more: Hybridization, Molecular Geometry, and Polarity of KrF2 Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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