AlCl3 Lewis structure

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AlCl3 Lewis Structure
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.


Use these steps to correctly draw the AlCl3 Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required

Let’s discuss each step in more detail.

#1 First draw a rough sketch

  • First, determine the total number of valence electrons
Periodic table

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

  • 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
AlCl3 Lewis Structure (Step 1)
Rough sketch of AlCl3 Lewis structure

#2 Mark lone pairs on the atoms

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:

AlCl3 Lewis Structure (Step 2)
Lone pairs marked, and got the stable Lewis structure of AlCl3

#3 Calculate and mark formal charges on the atoms, if required

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.

In the above structure, you can see that the central atom (aluminum) doesn’t form an octet. But, aluminum has an exception that it does not require eight electrons to form an octet. So no need to worry about the octet rule here.

Therefore, this structure is the stable Lewis structure of AlCl3.

Next: BeH2 Lewis structure

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