AlBr3 Molecular Geometry

Aluminium tribromide(AlBr3) has the composition of one aluminium and three bromine atoms. What is the molecular geometry of aluminium tribromide?. Drawing and predicting the AlBr3 molecular geometry is very easy by following the given method. Here in this post, we described step by step to construct AlBr3 molecular geometry. bromine and aluminium come from the 17th and 13th family groups in the periodic table. Bromine and aluminium have seven and three valence electrons respectively.

Key Points To Consider When drawing The AlBr3 Molecular Geometry

A three-step approach for drawing the AlBr3 molecular can be used. The first step is to sketch the molecular geometry of the AlBr3 molecule, to calculate the lone pairs of the electron in the central aluminium atom; the second step is to calculate the AlBr3 hybridization, and the third step is to give perfect notation for the AlBr3 molecular geometry.

The AlBr3 molecular geometry is a diagram that illustrates the number of valence electrons and bond electron pairs in the AlBr3 molecule in a specific geometric manner. The geometry of the AlBr3 molecule 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 AlBr3 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 Al-Br bond (dipole moment properties of the AlBr3 molecular geometry). The aluminium-bromine bonds in the aluminium tribromide(AlBr3), for example, are polarised toward the more electronegative value bromine atom, and because all (Al-Br) bonds have the same size and polarity, their sum is zero due to the AlBr3 molecule’s bond dipole moment due to it oppose to each other in the trigonal planar geometry, and the AlBr3 molecule is classified as a nonpolar molecule.

AlBr3 Molecular Geometry

The molecule of aluminium tribromide (with trigonal planar shape AlBr3 molecular geometry) is tilted at 120 degrees bond angle of Br-Al-Br. It has a difference in electronegativity values between aluminium and bromine atoms, with bromine’s pull the electron cloud being greater than aluminium’s. But bond polarity of Al-Br is cancelled to each other in the trigonal planar geometry. As a result, it has no permanent dipole moment in its molecular structure. The AlBr3 molecule has no dipole moment due to an equal charge distribution of negative and positive charges.

Overview: AlBr3 electron and molecular geometry

According to the VSEPR theory, AlBr3 possesses trigonal planar molecular geometry. Because the center atom, aluminium, has three Al-Br bonds with the bromine atoms surrounding it. The Br-Al-Br bond angle is 120 degrees in the trigonal planar molecular geometry. The AlBr3 molecule has a trigonal planar geometry shape because it contains three bromine atoms.

There are three Al-Br bonds at the AlBr3 molecular geometry. After linking the three bromine atoms and no lone pairs of electrons in the trigonal planar form, it maintains the planar-T-like structure. In the AlBr3 molecular geometry, the Al-Br bonds have stayed in the three terminals and no lone pairs of electrons in the top and bottom of the trigonal planar molecule.

The center aluminium atom of AlBr3 has no lone pairs of electrons, resulting in trigonal planar electron geometry. However, the molecular geometry of AlBr3 looks like a trigonal planar and no lone pairs on the top and bottom of the AlBr3 geometry. It’s the AlBr3 molecule’s symmetrical geometry. As a result, the AlBr3 molecule is nonpolar.

How to find AlBr3 hybridization and molecular geometry

Calculating lone pairs of electrons on aluminium in the AlBr3 geometry:

  1. Determine the number of lone pairs on the core aluminium atom of the AlBr3 Lewis structure. Because the lone pairs on aluminium are mostly responsible for the AlBr3 molecule geometry distortion, we need to calculate out how many there are on the central aluminium atom of the Lewis structure.

Use the formula below to find the lone pair on the aluminium atom of the AlBr3 molecule.

L.P(Al) = V.E(Al) – N.A(Al-Br)/2

Lone pair on the central aluminium atom = L.P(Al)

The core central aluminium atom’s valence electron = V.E(Al)

Number of Al-Br bonds = N.A (Al-Br)

calculation for aluminium atom lone pair in AlBr3 molecule

For instance of AlBr3, the central atom, aluminium, has three electrons in its outermost valence shell, three Al-Br bond connections.

As a result of this, L.P(Al) = (3 –3)/2=0

In the AlBr3 electron geometry structure, the lone pair on the central aluminium atom is zero. It means there are no lone pairs of electrons in the core aluminium atom. This makes the AlBr3 molecule electron deficient. It makes coordination with ammonia. No lone pairs of electrons on the central aluminium atom are responsible for the planar nature of AlBr3 molecular geometry.

If you imagine, there is no lone pair on the aluminium atom of the AlBr3 molecule. Then, electronic repulsion of Al-Br bonds pair and zero lone pair of electrons in the AlBr3. That gives stable trigonal planar geometry. No lone pairs of electrons are located on the top and bottom of the geometry. It makes a stable trigonal planar structure.

But in reality, the AlBr3 molecule undergoes distortion in its geometry due to the polarity of the Al-Br bond and no lone pairs of electrons in the trigonal planar geometry. This leads to a trigonal planar for the AlBr3 molecule.

Calculate the number of molecular hybridizations of the AlBr3 molecule

What is AlBr3 hybridization? This is a very fundamental question in the field of molecular chemistry. All the molecules made by atoms. In chemistry, atoms are the fundamental particles. There are four different types of orbitals in chemistry. They are named as 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

AlBr3 molecule is made of one aluminium and three bromine atoms. The aluminium atom has s and p orbitals. Bromine comes as the third element from the halogen family in the periodic table. The bromine atom has s and p orbitals.

When these atoms combine to form the AlBr3 molecule, its atomic orbitals mixed and form unique molecular orbitals due to hybridization.

How do you find the AlBr3 molecule’s hybridization? We must now determine the molecular hybridization number of AlBr3.

The formula of AlBr3 molecular hybridization is as follows:

No. Hyb of AlBr3= N.A(Al-Br bonds) + L.P(Al)

No. Hy of AlBr3= the number of hybridizations of AlBr3

Number of Al-Br bonds = N.A (Al-Br bonds)

Lone pair on the central aluminium atom = L.P(Al)

Calculation for hybridization number for AlBr3 molecule

In the AlBr3 molecule, the aluminium is a core central atom with three bromine atoms connected to it and no lone pairs of electrons. The number of AlBr3 hybridizations (No. Hyb of AlBr3) can then be estimated using the formula below.

No. Hyb of AlBr3= 3+0 =3

The AlBr3 molecule hybridization is three. The aluminium atom has s and p orbitals. The bromine atom has s and p orbital. The sp2 hybridization of the AlBr3 molecule is formed when one S orbital and two p orbitals join together to form a molecular orbital.

Molecular Geometry Notation for AlBr3 Molecule :

Determine the form of AlBr3 molecular geometry using VSEPR theory. The AXN technique is commonly used when the VSEPR theory is used to calculate the shape of the AlBr3 molecule.

The AXN notation of AlBr3 molecule is as follows:

The center aluminium atom in the AlBr3 molecule is denoted by the letter A.

The bound pairs (three Al-Br bonds) of electrons to the core aluminium atom are represented by X.

The lone pairs of electrons on the central aluminium atom are denoted by the letter N.

Notation for AlBr3 molecular geometry

We know that aluminium is the core atom, with three electron pairs bound (three Al-Br) and zero lone pair of electrons. The general molecular geometry formula for AlBr3 is AX3.

According to the VSEPR theory, if the AlBr3 molecule has an AX3 generic formula, the molecular geometry and electron geometry will both be trigonal planar forms.

Name of MoleculeAluminium tribromide
Chemical molecular formulaAlBr3
Molecular geometry of AlBr3Trigonal planar
Electron geometry of AlBr3Trigonal planar
Hybridization of AlBr3sp2
Bond angle (Br-Al-Br)120º degree
Total Valence electron for AlBr324
The formal charge of AlBr3 on aluminium0


In this post, we discussed the method to construct AlBr3 molecular geometry, the method to find the lone pairs of electrons in the central aluminium atom, AlBr3 hybridization, and AlBr3 molecular notation. Need to remember that, if you follow the above-said method, you can construct the AlBr3 molecular structure very easily.

What is AlBr3 Molecular geometry?

AlBr3 Molecular geometry is an electronic structural representation of molecules.

What is the molecular notation for AlBr3 molecule?

AlBr3 molecular notation is AX3.

The polarity of the molecules

The polarity of the molecules are listed as follows

Lewis Structure and Molecular Geometry

Lewis structure and molecular geometry of molecules are listed below

External References

Information on aluminium tribromide(AlBr3) molecule

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