BF3 Lewis structure

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BF3 Lewis Structure
BF3 Lewis structure | Image: Learnool

BF3 (boron trifluoride) has one boron atom and three fluorine atoms.

In the BF3 Lewis structure, there are three single bonds around the boron atom, with three fluorine atoms attached to it, and on each fluorine atom, there are three lone pairs.


Use these steps to correctly draw the BF3 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 | Image: Learnool

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

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

Since BF3 has one boron atom and three fluorine atoms, so…

Valence electrons of one boron atom = 3 × 1 = 3
Valence electrons of three fluorine 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 fluorine, assume that the central atom is boron.

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

  • And finally, draw the rough sketch
BF3 Lewis Structure (Step 1)
Rough sketch of BF3 Lewis structure | Image: Learnool

#2 Mark lone pairs on the atoms

Here, we have a total of 12 electron pairs. And three B — 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 both (boron and fluorine) are the period 2 elements, so they can not keep more than 8 electrons in their 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 boron, there is zero lone pair because all nine electron pairs are over.

Mark the lone pairs on the sketch as follows:

BF3 Lewis Structure (Step 2)
Lone pairs marked, and got the stable Lewis structure of BF3 | Image: Learnool

#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 boron atom, formal charge = 3 – 0 – ½ (6) = 0

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

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

In the above structure, you can see that the central atom (boron) doesn’t form an octet. But, boron 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 BF3.

Next: NO3 Lewis structure

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Deep was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.

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