BCl3 Lewis structure

BCl₃ (boron trichloride) has one boron atom and three chlorine atoms.

In the BCl₃ Lewis structure, there are three single bonds around the boron atom, with three chlorine atoms attached to it, and on each chlorine atom, there are three lone pairs.

Alternative method: Lewis structure of BCl₃

Rough sketch

• First, determine the total number of valence electrons

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

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

Since BCl₃ has one boron atom and three chlorine atoms, so…

Valence electrons of one boron 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: Boron 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 boron is less electronegative than chlorine, assume that the central atom is boron.

Therefore, place boron 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 B — 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 boron is a period 2 element, so it can not keep more than 8 electrons in its last shell. And chlorine is a period 3 element, so it can keep more than 8 electrons in its 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 boron, 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 boron atom, formal charge = 3 – 0 – ½ (6) = 0

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

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

Final structure

The final structure of BCl₃ includes a central boron atom connected to three chlorine atoms through single covalent bonds. In this layout, the boron atom serves as an exception to the octet rule, existing in a stable state with an incomplete valence shell of only six electrons. Each chlorine atom satisfies its octet by retaining three lone pairs in addition to its 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. Therefore, this specific electronic distribution serves as the definitive and most accurate Lewis representation of boron trichloride.

Next: CF₄ Lewis structure

External video

• BCl3 Lewis Structure – How to Draw the Lewis Structure for BCl3 – YouTube • Wayne Breslyn

External links

• https://geometryofmolecules.com/bcl3-lewis-structure-molecular-geometry-hybridization-shape/
• https://techiescientist.com/bcl3-lewis-structure/
• https://topblogtenz.com/bcl3-lewis-structure-molecular-geometry-bond-angle-hybridization/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/BCl3-lewis-structure.html
• https://lambdageeks.com/bcl3-lewis-structure/