Geometry, Hybridization, and Polarity of AlCl3 Lewis Structure

Aluminum chloride is a chemical compound that is made up of inorganic elements. AlCl3 is a corrosive solid that is odourless and white/pale yellow in colour. It comes in two forms: hydrated (AlCl3.6H2O) and anhydrous (AlCl3.6H2O) (AlCl3).

We will learn how to predict Lewis structure, geometry, hybridization, and polarity of a given compound in this article.

Structure of Lewis

Lewis Structure is a two-dimensional representation of atoms in a compound and the valence shell electrons on those atoms.

Many attempts have been made to explain how chemical bonds form. Lewis was one of the first to offer an explanation. Because he believes that only valence electrons participate in bonding, he only considers valence electrons in his representation.

Valence shell electrons are represented by dots on the chemical symbol of elements in this manner.

Some compounds have the potential to have multiple Lewis structures. We must meet the octet rule and formal charges on all constituent atoms to find the most accurate and lowest energy structure.

The Rule of the Octet

In the periodic table, noble gases are the least reactive and most stable. To achieve a noble gas-like structure, each element forms a bond.

Except for He, all noble gases have eight electrons in their valence shell.

As a result, after bonding, all main group elements prefer to have a fully filled configuration with a net of 8 electrons in their valence shell. The octet rule is named after its preference for eight electrons.

Charge Formal

It’s a purely theoretical idea. The number of valence electrons in an isolated neutral atom is compared to the number of valence electrons in a molecule’s bound state. It’s calculated with the following formula:

Charge in formal terms= (number of electrons in an isolated neutral atom)

– (number of nonbonding electrons on an atom in the compound)

-0.5 * (number of electrons shared in bonds by atom)

How to Draw the Lewis Structure of AlCl3 in Steps

Step 1: Count the total number of electrons in the valence shell of the chemical.

Atom Atomic NumberGroup NumberValence  electrons according to  group numberElectronic configuration (E.C.)Valence shell from E.C.Valence electrons from E.C.
One Al 13 13 1s2 2s2 2p6 3s2 3p1 n=3 3
Three Cl 17 17 1s2 2s2 2p6 3s2 3p5 n=3 7
Total number of valence shell electrons= 3 + (7*3) = 24

Step 2: For elements, draw the Lewis dot structure.

The Lewis structure of an element is drawn by arranging the valence shell electrons around the chemical symbol of the element.

Aluminum and chlorine have the chemical symbols Al and Cl, respectively. For Al and Cl, the Lewis dot structure is as follows:

Step 3: Pick a good core atom for your chemical.

Because the centre atom is expected to share its electron density with the other atoms, it should be the least electronegative of the constituent atoms.

As a result, Al is the compound’s core atom.

Step 4: Sketch down a skeleton diagram.

In this phase, we must properly organise the side and central atoms.

Arrange the valence electrons around the elemental symbols in step 5.

The total valence shell electrons (estimated in step 1) are arranged according to a bond formation anticipated. Electrons from Al are represented by blue dots, while electrons from Cl are represented by black dots.

Step 6: Form bonds to complete the octet of atoms.

In the solitary state, each Cl contains seven valence electrons. To have a fully filled valence shell structure, they share one electron with Al.

In its isolated state, Al possesses three valence electrons. Even though it shares one electron with all Cl-atoms, the octet does not complete.

The octet is not complete in any other Lewis structure. It is an electron-deficient compound because it is always missing two electrons.

Step 7: Determine all atoms’ formal charges.

This chemical has a net charge of zero. As a result, the total formal charge on three atoms should equal zero.

Atom Total number of  valence electrons in a free atomTotal number of  non-bonding electrons(Total number of  bonding electrons)*0.5Formal Charge
Al 6*0.5=3 3-0-3=0
Cl1 2*0.5=1 7-6-1=0
Cl2 2*0.5=1 7-6-1=0
Cl3 2*0.5=1 7-6-1=0

As a result, the Lewis structure developed in step 6 is the best for AlCl3.

A video showing how to sketch the Lewis structure of AlCl3 is attached. You are free to look through it.

Geometry of AlCl3

Lewis structure makes no attempt to predict the geometry and shape of molecules. We have another hypothesis called VSEPR theory for the geometry.

The 3D arrangement of atoms in a molecule is known as molecular geometry.

The valence shell electron pair repulsion theory is abbreviated as VSEPR.

The VSEPR theory states that

• Because the valence electron pairs resist each other, the system becomes unstable.

• To make the electron configuration stable, the repulsions between them must be reduced.

• As a result, electrons align themselves with the least amount of repulsion and the greatest distance between them.

• The molecule geometry is determined by the stable arrangement of atoms’ valence electron pairs.

Bonding pairs of electrons (bp) are valence shell electrons that are involved in bonding, while lone pairs of electrons are valence shell electrons that are not involved in bonding (lp).

You should also read my post on whether AlCl3 is ionic or covalent.

How to Use VSEPR to Predict AlCl3 Geometry

  1. Determine A by counting the number of valence shell electrons on the centre atom (arbitrary variable).

Al is the core atom in the compound AlCl3. The valence electrons in Al are three. (Shown in step 1 of the Lewis structure drawing)

A=3

  1. Determine the number of side atoms and multiply by B. (arbitrary variable).

There are three side atoms (chlorine) and B=3 in AlCl3.

  1. If the compound is charged, deduct the charge from B for positively charged compounds and add the charge to B for negatively charged compounds if the compound is charged. For neutral substances, this step might be skipped.

There is no charge contribution in AlCl3, and B=3 is the only value.

  1. Add the contributions of the side atoms and charge to the centre atom’s contribution, i.e. A+B.

A+B=6 for AlCl3.

  1. Multiply A+B by 2 to get the total number of electron pairs influencing the form.

There are three electron pairs in AlCl3.

  1. Separate the total electron pairs into bonding and non-bonding electron pairs. The number of side atoms equals the number of bonding electron pairs.

There are three side atoms in AlCl3. As a result, there are three electron bonding pairs and zero nonbonding pairs.

The following table can be used to forecast geometry and shape based on this information.

AlCl3 has a trigonal planar electron geometry and form. Compounds with zero lone pairs have the same geometry and form.

Hybridization of AlCl3

We need a new paradigm to describe the bonding in some polyatomic molecules, such as methane. Hybridization is the term for this notion.

Hybridization is the process of combining atomic orbitals of similar energy, size, and shape to create equivalent orbitals. It is concerned with energy redistribution.

There is no genuine mixing; only wavefunction mixing occurs.

One 3s orbital and three 3p orbitals, for example, can combine to generate four sp3 hybrid orbitals, while 1s and 5p cannot.

The core atom in AlCl3 is Al.

Al’s electrical arrangement in its ground state is 1s2 2s2 2p6 3s2 3p1. In hybridization, only valence orbitals are utilised.

In the excited state, one electron of the 3s orbital is promoted to the 3p orbital.

These three orbitals (one 3s and two 3p) are now hybridised to produce three sp2 orbitals, which will establish bonds with nearby chlorine atoms’ p orbitals. Al has one unoccupied p orbital.

As a result, AlCl3 is sp2 hybridised.

The formula for determining the type of AlCl3 hybridization

In the last step of VSEPR theory, we estimated the total electron pairs. It was found to be 3 for AlCl3.

Using total electron pairs or steric numbers, the table below can predict hybridization.

The number of (sigma bonds + a lone pair on the central atom) sterics is equal to the number of (sigma bonds + a lone pair on the central

AlCl3 has a steric number of (3+0)=3.

The chart shows that hybridization is sp2.

Polarity of AlCl3

The existence or absence of a net dipole moment can be used to determine the polarity of a chemical. A compound’s net dipole moment is determined by-

• The bond’s dipole moment

• The electronegativity difference between the atoms that make up the bonds

• Compound geometry and symmetry

A vector quantity is the dipole moment. There is only one type of bond in AlCl3: “Al-Cl.”

Al and Cl have electronegativity of 1.61 and 3.16, respectively. 1.55 is the result of the difference. As a result, the bonds are polar, and the bond dipole moment is greater than zero.

A polar molecule does not have to have polar bonds.

Due to the trigonal planar geometry, the vector’s sum of the dipole moments of the three bonds equals zero. The three vectors form a 120-degree angle and cancel each other out.

As a result, AlCl3 is a polar molecule.

Conclusion

AlCl3 is a metal halide that is inorganic.

Because Al’s octet is not full, it is an electron-deficient molecule.

Aluminum chloride can be represented by the Lewis structure shown in the previous section. The trigonal planar molecular geometry and form are revealed.

The core atom, Al, has undergone sp2 hybridization.

Aluminum chloride is a nonpolar substance.

Good luck with your reading!

Read more: Lemon pH: Is it Acidic or Basic?

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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