AlCl3 Molecular Geometry

Aluminium trichloride(AlCl3) has the composition of one Aluminium and three chlorine atoms. What is the molecular geometry of Aluminium trichloride?. Drawing and predicting the AlCl3 molecular geometry is very easy by following the given method. Here in this post, we described step by step to construct AlCl3 molecular geometry. Chlorine and Aluminium come from the 17th and 13th family groups in the periodic table. Chlorine and Aluminium have seven and three valence electrons respectively.

Key Points To Consider When drawing The AlCl3 Molecular Geometry

A three-step approach for drawing the AlCl3 molecular can be used. The first step is to sketch the molecular geometry of the AlCl3 molecule, to calculate the lone pairs of the electron in the central Aluminium atom; the second step is to calculate the AlCl3 hybridization, and the third step is to give perfect notation for the AlCl3 molecular geometry.

The AlCl3 molecular geometry is a diagram that illustrates the number of valence electrons and bond electron pairs in the AlCl3 molecule in a specific geometric manner. The geometry of the AlCl3 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 AlCl3 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-Cl bond (dipole moment properties of the AlCl3 molecular geometry). The Aluminium-chlorine bonds in the Aluminium trichloride(AlCl3), for example, are polarised toward the more electronegative value chlorine atom, and because all (Al-Cl) bonds have the same size and polarity, their sum is zero due to the AlCl3 molecule’s bond dipole moment due to it oppose to each other in the trigonal planar geometry, and the AlCl3 molecule is classified as a nonpolar molecule.

AlCl3 Molecular Geometry

The molecule of Aluminium trichloride (with trigonal planar shape AlCl3 molecular geometry) is tilted at 120 degrees bond angle of Cl-Al-Cl. It has a difference in electronegativity values between Aluminium and chlorine atoms, with chlorine’s pull the electron cloud being greater than Aluminium’s. But bond polarity of Al-Cl is cancelled to each other in the trigonal planar geometry. As a result, it has no permanent dipole moment in its molecular structure. The AlCl3 molecule has no dipole moment due to an equal charge distribution of negative and positive charges.

Overview: AlCl3 electron and molecular geometry

According to the VSEPR theory, AlCl3 possesses trigonal planar molecular geometry. Because the center atom, Aluminium, has three Al-Cl bonds with the chlorine atoms surrounding it. The Cl-Al-Cl bond angle is 120 degrees in the trigonal planar molecular geometry. The AlCl3 molecule has a trigonal planar geometry shape because it contains three chlorine atoms.

There are three Al-Cl bonds at the AlCl3 molecular geometry. After linking the three chlorine atoms and no lone pairs of electrons in the trigonal planar form, it maintains the planar-T-like structure. In the AlCl3 molecular geometry, the Al-Cl 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 AlCl3 has no lone pairs of electrons, resulting in trigonal planar electron geometry. However, the molecular geometry of AlCl3 looks like a trigonal planar and has no lone pairs on the top and bottom of the AlCl3 geometry. It’s the AlCl3 molecule’s symmetrical geometry. As a result, the AlCl3 molecule is nonpolar.

How to find AlCl3 hybridization and molecular geometry

Calculating lone pairs of electrons on Aluminium in the AlCl3 geometry:

1.Determine the number of lone pairs on the core Aluminium atom of the AlCl3 Lewis structure. Because the lone pairs on Aluminium are mostly responsible for the AlCl3 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 AlCl3 molecule.

L.P(Al) = V.E(Al) – N.A(Al-Cl)/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-Cl bonds = N.A (Al-Cl)

calculation for aluminium atom lone pair in AlCl3 molecule

For instance of AlCl3, the central atom, Aluminium, has three electrons in its outermost valence shell, three Al-Cl bond connections.

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

In the AlCl3 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 AlCl3 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 AlCl3 molecular geometry.

If you imagine, there is no lone pair on the Aluminium atom of the AlCl3 molecule. Then, electronic repulsion of Al-Cl bonds pair and zero lone pair of electrons in the AlCl3. 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 AlCl3 molecule undergoes distortion in its geometry due to the polarity of the Al-Cl bond and no lone pairs of electrons in the trigonal planar geometry. This leads to a trigonal planar for the AlCl3 molecule.

Calculate the number of molecular hybridizations of the AlCl3 molecule

What is AlCl3 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

AlCl3 molecule is made of one Aluminium and three chlorine atoms. The Aluminium atom has s and p orbitals. Chlorine comes as the second element from the halogen family in the periodic table. The chlorine atom has s and p orbitals.

When these atoms combine to form the AlCl3 molecule, its atomic orbitals mix and form unique molecular orbitals due to hybridization.

How do you find the AlCl3 molecule’s hybridization? We must now determine the molecular hybridization number of AlCl3.

The formula of AlCl3 molecular hybridization is as follows:

No. Hyb of AlCl3= N.A(Al-Cl bonds) + L.P(Al)

No. Hy of AlCl3= the number of hybridizations of AlCl3

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

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

Calculation for hybridization number for AlCl3 molecule

In the AlCl3 molecule, the Aluminium is a core central atom with three chlorine atoms connected to it and no lone pairs of electrons. The number of AlCl3 hybridizations (No. Hyb of AlCl3) can then be estimated using the formula below.

No. Hyb of AlCl3= 3+0 =3

The AlCl3 molecule hybridization is three. The Aluminium atom has s and p orbitals. The chlorine atom has s and p orbital. The sp2 hybridization of the AlCl3 molecule is formed when one S orbital and two p orbitals join together to form a molecular orbital.

Molecular Geometry Notation for AlCl3 Molecule :

Determine the form of AlCl3 molecular geometry using VSEPR theory. The AXN technique is commonly used when the VSEPR theory is used to calculate the shape of the AlCl3 molecule.

The AXN notation of AlCl3 molecule is as follows:

The center aluminium atom in the AlCl3 molecule is denoted by the letter A.

The bound pairs (three Al-Cl 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 AlCl3 molecular geometry

We know that Aluminium is the core atom, with three electron pairs bound (three Al-Cl) and zero lone pair of electrons. The general molecular geometry formula for AlCl3 is AX3.

According to the VSEPR theory, if the AlCl3 molecule has an AX3 generic formula, the molecular geometry and electron geometry will both be trigonal planar forms.

Name of MoleculeAluminium trichloride
Chemical molecular formulaAlCl3
Molecular geometry of AlCl3Trigonal planar
Electron geometry of AlCl3Trigonal planar
Hybridization of AlCl3sp2
Bond angle (Cl-Al-Cl)120º degree
Total Valence electron for AlCl324
The formal charge of AlCl3 on Aluminium0


In this post, we discussed the method to construct AlCl3 molecular geometry, the method to find the lone pairs of electrons in the central Aluminium atom, AlCl3 hybridization, and AlCl3 molecular notation. Need to remember that, if you follow the above-said method, you can construct the AlCl3 molecular structure very easily.

What is AlCl3 Molecular geometry?

AlCl3 Molecular geometry is an electronic structural representation of molecules.

What is the molecular notation for AlCl3 molecule?

AlCl3 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 trichloride(AlCl3) molecule

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