BCl2 Lewis structure

BCl₂ has one boron atom and two chlorine atoms.

In BCl₂ Lewis structure, there are two single bonds around the boron atom, with two chlorine atoms attached to it. Each chlorine atom has three lone pairs, and the boron atom has one lone pair.

Alternative method: Lewis structure of BCl₂

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 BCl₂ has one boron atom and two chlorine atoms, so…

Valence electrons of one boron atom = 3 × 1 = 3
Valence electrons of two chlorine atoms = 7 × 2 = 14

And the total valence electrons = 3 + 14 = 17

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

• Second, find the total electron pairs

We have a total of 17 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

But 17 can not be divided by two. Hence, there are a total of 8 electron pairs and one unpaired electron.

• Third, determine the central atom

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

Since boron is less electronegative than fluorine, 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 8 electron pairs and one unpaired electron. And two B — Cl bonds are already marked. So we have to only mark the remaining six electron pairs and one unpaired electron 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 one unpaired electron.

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 – 1 – ½ (4) = 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 BCl₂ features a central boron atom connected to two chlorine atoms through single covalent bonds. In this arrangement, the boron atom serves as an exception to the octet rule, possessing an incomplete valence shell with only five electrons: four bonding electrons and one unpaired electron. Each chlorine atom fulfills its octet by maintaining three lone pairs of its own alongside the single shared bond. This configuration represents a radical species, where the formal charges on all atoms are zero, making it the most stable electronic state for this specific unit. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of BCl₂.

Next: AsI₃ Lewis structure