BCl3 Lewis Structure

BCl3 Lewis Structure

BCl3 (boron trichloride) has one boron atom and three chlorine atoms. In the lewis structure of BCl3, there are three single bonds around the boron atom, with three chlorine atoms attached to it. Each chlorine atom has three lone pairs, and the boron atom has one lone pair.

Steps

Here’s how you can draw the BCl3 lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges (if there are)

Let’s break down each step in detail.

#1 Draw 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

  • 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
BCl3 Lewis Structure (Step 1)

#2 Mark Lone Pairs

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:

BCl3 Lewis Structure (Step 2)

#3 Mark Charges

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.

And in the above structure, you can see that the central atom (boron) forms an octet. Hence, the octet rule is satisfied.

Therefore, this structure is the stable lewis structure of BCl3.

Next: CF4 Lewis Structure

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