AlF3 Lewis structure

AlF₃ (aluminum fluoride) has one aluminum atom and three fluorine atoms.

In the AlF₃ Lewis structure, there are three single bonds around the aluminum atom, with three fluorine atoms attached to it, and on each fluorine atom, there are three lone pairs.

Alternative method: Lewis structure of AlF₃

Rough sketch

• First, determine the total number of valence electrons

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

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

Since AlF₃ has one aluminum atom and three fluorine atoms, so…

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

And the total valence electrons = 3 + 21 = 24

Learn how to find: Aluminum valence electrons and Fluorine 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 fluorine, assume that the central atom is aluminum.

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

• And finally, draw the rough sketch

Lone pair

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

Also remember that aluminum is a period 3 element, so it can keep more than 8 electrons in its last shell. And fluorine is a period 2 element, so it can not keep more than 8 electrons in its last shell.

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

So for each fluorine, 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 fluorine atom, formal charge = 7 – 6 – ½ (2) = 0

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

Final structure

The final structure of AlF₃ includes a central aluminum atom connected to three fluorine atoms through single covalent bonds. In this layout, the aluminum atom acts as an electron-deficient center, typically remaining stable with only six valence electrons in its bonding shell, while each fluorine atom satisfies the octet rule by maintaining three lone pairs alongside its single shared bond. This arrangement is the most stable because it results in a formal charge of zero for the aluminum atom and all three fluorine atoms. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of aluminum trifluoride.

Next: TeF₄ Lewis structure

External video

• How to Draw the Lewis Dot Structure for AlF3: Aluminum fluoride – YouTube • Wayne Breslyn

External links

• https://lambdageeks.com/alf3-lewis-structure/