AlCl3 Lewis structure

AlCl₃ (aluminum chloride) has one aluminum atom and three chlorine atoms.

In the AlCl₃ Lewis structure, there are three single bonds around the aluminum atom, with three chlorine atoms attached to it, and on each chlorine atom, there are three lone pairs.

Alternative method: Lewis structure of AlCl₃

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, aluminum lies in group 13, and chlorine lies in group 17.

Hence, aluminum has three valence electrons and chlorine has seven valence electrons.

Since AlCl₃ has one aluminum atom and three chlorine atoms, so…

Valence electrons of one aluminum atom = 3 × 1 = 3
Valence electrons of three chlorine atoms = 7 × 3 = 21

And the total valence electrons = 3 + 21 = 24

Learn how to find: Aluminum valence electrons and Chlorine valence electrons

• Second, find the total electron pairs

We have a total of 24 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 24 ÷ 2 = 12

• Third, determine the central atom

We have to place the least electronegative atom at the center.

Since aluminum is less electronegative than chlorine, assume that the central atom is aluminum.

Therefore, place aluminum in the center and chlorines on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 12 electron pairs. And three Al — Cl bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that both (aluminum and chlorine) are the period 3 elements, so they can keep more than 8 electrons in their last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are chlorines.

So for each chlorine, there are three lone pairs, and for aluminum, there is zero lone pair because all nine electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For aluminum atom, formal charge = 3 – 0 – ½ (6) = 0

For each chlorine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, both aluminum and chlorine atoms do not have charges, so no need to mark the charges.

Final structure

The final structure of AlCl₃ has a central aluminum atom connected to three chlorine atoms through single covalent bonds. In this setup, the aluminum atom serves as an exception to the octet rule, reaching stability with only six valence electrons across its three bonding pairs. Each chlorine atom fulfills its octet by maintaining three lone pairs of its own alongside the single shared bond. This arrangement is the most stable because it results in formal charges of zero for every atom, representing the most energetically favorable state for the molecule. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of aluminum chloride.

Next: BeH₂ Lewis structure

External video

• How to Draw the Lewis Structure for AlCl3: Aluminum chloride – YouTube • Wayne Breslyn

External links

• https://techiescientist.com/alcl3-lewis-structure/
• https://www.chemistryscl.com/general/Aluminium-chloride-AlCl3-lewis-structure/index.php
• https://topblogtenz.com/alcl3-lewis-structure-molecular-geometry-polarity/
• https://geometryofmolecules.com/alcl3-lewis-structure-molecular-structure-hybridization-bond-angle-shape/
• https://lambdageeks.com/alcl3-lewis-structure/
• https://sciedutut.com/alcl3-lewis-structure/