PBr3 Molecular Geometry - Science Education and Tutorials

Q: What is the molecular notation for PBr3 molecule?

PBr3 molecular notation is AX3N1.

Phosphorus tribromide(PBr3) has the composition of one phosphorus and three bromine atoms. What is the molecular geometry of phosphorus tribromide?. Drawing and predicting the PBr3 molecular geometry is very easy by following the given method. Here in this post, we described step by step to construct PBr3 molecular geometry. Phosphorus and bromine come from the 15th and 17th family groups in the periodic table. Phosphorus and bromine have five and seven valence electrons respectively.

Table of Contents

Key Points To Consider When drawing The PBr3 Molecular Geometry

A three-step approach for drawing the PBr3 molecular can be used. The first step is to sketch the molecular geometry of the PBr3 molecule, to calculate the lone pairs of the electron in the central phosphorus atom; the second step is to calculate the PBr3 hybridization, and the third step is to give perfect notation for the PBr3 molecular geometry.

The PBr3 molecular geometry is a diagram that illustrates the number of valence electrons and bond electron pairs in the PBr3 molecule in a specific geometric manner. The geometry of the PBr3 molecule ion can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory) and molecular hybridization theory, which states that molecules will choose the PBr3 geometrical shape in which the electrons have from one another in the specific molecular structure.

Finally, you must add their bond polarities characteristics to compute the strength of the three P-Br single bonds (dipole moment properties of the PBr3 molecular geometry). Two phosphorus-bromine single bonds in the phosphorus tribromide(PBr3), for example, are polarised toward the more electronegative value bromine atoms, and because all three (P-Br) single bonds have the same size and polarity, their sum is nonzero due to the PBr3 molecule’s bond dipole moment due to pulling the electron cloud to the three side of trigonal pyramidal geometry, and the PBr3 molecule is classified as a polar molecule.

The molecule of phosphorus tribromide(with trigonal pyramidal shape PBr3 molecular geometry) is tilted at 101.5 degrees bond angle of Br-P-Br. It has a difference in electronegativity values between phosphorus and bromine atoms, with bromine’s pull the electron cloud being greater than phosphorus’s. But bond polarity of P-Br is not canceled to each other in the trigonal pyramidal geometry. As a result, it has a nonzero permanent dipole moment in its molecular structure. The PBr3 molecule has a nonzero dipole moment due to an unequal charge distribution of negative and positive charges in the trigonal pyramidal geometry.

Overview: PBr3 electron and molecular geometry

According to the VSEPR theory, the PBr3 molecule ion possesses trigonal pyramidal molecular geometry. Because the center atom, phosphorus, has three P-Br single bonds with the three bromine atoms surrounding it. The Br-P-Br bond angle is 101.5 degrees in the trigonal pyramidal PBr3 molecular geometry. The PBr3 molecule has a trigonal pyramidal geometry shape because it contains three bromine atoms in the geometry and four corners with one lone pair of electrons.

There are three P-Br single bonds at the PBr3 molecular geometry. After linking the three bromine atoms and one lone pair of electrons on the phosphorus atom in the trigonal pyramidal form, it maintains the pyramidal-shaped structure. In the PBr3 molecular geometry, the P-Br single bonds have stayed in the three terminals and one lone pair of electrons on the phosphorus atom of the trigonal pyramidal PBr3 molecule.

The center phosphorus atom of PBr3 has one lone pair of electrons, resulting in trigonal pyramidal PBr3 electron geometry. However, the molecular geometry of PBr3 looks trigonal pyramidal and has one lone pair of electrons on the phosphorus of the PBr3 geometry. It’s the PBr3 molecule’s symmetrical geometry. As a result, the PBr3 molecule is polar.

How to find PBr3 hybridization and molecular geometry

Calculating lone pairs of electrons on phosphorus in the PBr3 geometry:

1.Determine the number of lone pairs of electrons in the core phosphorus atom of the PBr3 Lewis structure. Because the lone pairs of electrons on the phosphorus atom are mostly responsible for the PBr3 molecule geometry planar, we need to calculate out how many there are on the central phosphorus atom of the PBr3 Lewis structure.

Use the formula below to find the lone pair on the phosphorus atom of the PBr3 molecule.
L.P(P) = V.E(P) – N.A(P-Br)/2

Lone pair on the central phosphorus atom in PBr3 = L.P(P)
The core central phosphorus atom’s valence electron in PBr3 = V.E(P)
Number of P-Br bonds = N.A (P-Br)
calculation for phosphorus atom lone pair in PBr3 molecule.

For instance of PBr3, the central atom, phosphorus, has five electrons in its outermost valence shell, three P-Br single bond connections. This gives a total of three connections.

As a result of this, L.P(P) = (5 –3)/2=1

The lone pair of electrons in the phosphorus atom of the PBr3 molecule is one.

Calculating lone pair of electrons on bromine in the PBr3 geometry:

Finding lone pair of electrons for the terminal bromine atom is not similar to the central phosphorus atom. We use the following formula as given below

Use the formula below to find the lone pair on the bromine atom of the PBr3 molecule.
L.P(Br) = V.E(Br) – N.A(P-Br)

Lone pair on the terminal bromine atom in PBr3= L.P(Br)
Terminal bromine atom’s valence electron in PBr3= V.E(Br)
Number of P-Br bonds = N.A ( P-Br)
calculation for bromine atom lone pair in PBr3 molecule.

For instance of PBr3, their terminal atoms, bromine, have seven electrons in their outermost valence shell, one P-Br single bond connection. This gives a total of three P-Br single bond connections. But we are considering only one connection for the calculation.

As a result of this, L.P(Br) = (7 –1)=6

The lone pair of electrons in the bromine atom of the PBr3 molecule is six. Three bromine atoms are connected with the central phosphorus atom.

In the PBr3 electron geometry structure, the lone pair on the central phosphorus atom is one, lone pairs of electrons in the bromine atom have six. Three bromine atoms have 18 lone pairs of electrons.

It means there are one lone pair of electrons in the core phosphorus atom. One lone pair of electrons on the central phosphorus atom is responsible for the trigonal pyramidal nature of PBr3 molecular geometry. But in the structure bromine atoms are polarised sidewise in their trigonal pyramidal geometry.

The one lone pair of electrons are placed at the top of the PBr3 geometry. Because the Phosphorus atom is a lower electronegative value as compared with other atoms in the PBr3 molecule. Three bromine atoms are polarized towards the sidewise in the PBr3 structure.

But in reality, the PBr3 has one lone pair of electrons in its structure. This makes the PBr3 more asymmetrical in the structure of the molecule. Because there is electric repulsion between bond pairs and lone pairs. But some sort of interaction is there between bromine lone pairs and bond pairs. But it is negligible in the ground state.

But in the central, phosphorus atom has one lone pair of electrons and these lone pair electrons just oppose each other with phosphorus-bromine bond pairs.

Calculate the number of molecular hybridizations of the PBr3 molecule

What is PBr3 hybridization? This is a very fundamental question in the field of molecular chemistry. All the molecules are made of atoms. In chemistry, atoms are the fundamental particles. There are four different types of orbitals in chemistry. They are named s, p, d, and f orbitals.

The entire periodic table arrangement is based on these orbital theories. Atoms in the periodic table are classified as follows:

s- block elements
p- block elements
d-block elements
f-block elements
Atoms are classified in the periodic table

PBr3 molecule is made of one phosphorus, three bromine atoms. The bromine and phosphorus atoms have s and p orbitals. Bromine comes as the third element from the halogen family in the periodic table. The phosphorus atom also belongs to the nitrogen family group. But it falls as the second element in the periodic table.

When these atoms combine to form the PBr3 molecule, its atomic orbitals are mixed and form unique molecular orbitals due to hybridization.

How do you find the PBr3 molecule’s hybridization? We must now determine the molecular hybridization number of PBr3.

The formula of PBr3 molecular hybridization is as follows:
No. Hyb of PBr3= N.A(P-Br bonds) + L.P(P)
No. Hy of PBr3 = the number of hybridizations of PBr3
Number of P-Br bonds = N.A (P-Br bonds)
Lone pair on the central phosphorus atom = L.P(P)
Calculation for hybridization number for PBr3 molecule

In the PBr3 molecule, phosphorus is a core central atom with three bromine atoms connected to it. It has one lone pair of electrons on phosphorus. The number of PBr3 hybridizations (No. Hyb of PBr3) can then be estimated using the formula below.

No. Hyb of PBr3= 3+1=4

The PBr3 molecule ion hybridization is four. The phosphorus and bromine atoms have s and p orbitals. The sp3 hybridization of the PBr3 molecule is formed when one s orbital and three p orbitals join together to form the PBr3 molecular orbital.

Molecular Geometry Notation for PBr3 Molecule :

Determine the form of PBr3 molecular geometry using VSEPR theory. The AXN technique is commonly used when the VSEPR theory is used to calculate the shape of the PBr3 molecule.

The AXN notation of PBr3 molecule is as follows:
The central phosphorus atom in the PBr3 molecule is denoted by the letter A.
The bound pairs (three P-Br bonds) of electrons to the core phosphorus atom are represented by X.
The lone pairs of electrons on the central phosphorus atom are denoted by the letter N.
Notation for PBr3 molecular geometry

We know that phosphorus is the core atom, with two electron pairs bound (three P-Br) and one lone pair of electrons. The general molecular geometry formula for PBr3 is AX3N1.

According to the VSEPR theory, if the PBr3 molecule ion has an AX3N1 generic formula, the molecular geometry and electron geometry will both be trigonal pyramidal forms.

Name of Molecule	Phosphorus tribromide
Chemical molecular formula	PBr3
Molecular geometry of PBr3	Trigonal pyramidal
Electron geometry of PBr3	Trigonal pyramidal
Hybridization of PBr3	sp3
Bond angle (Br-P-Br)	101.5º degree
Total Valence electron for PBr3	26
The formal charge of PBr3 on phosphorus	0

Summary:

In this post, we discussed the method to construct PBr3 molecular geometry, the method to find the lone pairs of electrons in the central phosphorus atom, PBr3 hybridization, and PBr3 molecular notation. Need to remember that, if you follow the above-said method, you can construct the PBr3 molecular structure very easily.