So you have seen the above image by now, right?
Let me explain the above image in short.
BF3 lewis structure has a Boron atom (B) at the center which is surrounded by three Fluorine atoms (F). There are 3 single bonds between the Boron atom (B) and each Fluorine atom (F).
If you haven’t understood anything from the above image of BF3 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of BF3.
So let’s move to the steps of drawing the lewis structure of BF3.
Steps of drawing BF3 lewis structure
Step 1: Find the total valence electrons in BF3 molecule
In order to find the total valence electrons in BF3 molecule, first of all you should know the valence electrons present in boron atom as well as fluorine atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)
Here, I’ll tell you how you can easily find the valence electrons of boron as well as fluorine using a periodic table.
Total valence electrons in BF3 molecule
→ Valence electrons given by boron atom:
Boron is a group 13 element on the periodic table.  Hence the valence electrons present in boron is 3.
You can see the 3 valence electrons present in the boron atom as shown in the above image.
→ Valence electrons given by fluorine atom:
Fluorine is group 17 element on the periodic table.  Hence the valence electron present in fluorine is 7.
You can see the 7 valence electrons present in the fluorine atom as shown in the above image.
Total valence electrons in BF3 molecule = valence electrons given by 1 boron atom + valence electrons given by 3 fluorine atoms = 3 + 7(3) = 24.
Step 2: Select the central atom
For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.
Now here the given molecule is BF3 and it contains boron atom (B) and fluorine atoms (F).
You can see the electronegativity values of boron atom (B) and fluorine atom (F) in the above periodic table.
If we compare the electronegativity values of boron (B) and fluorine (F) then the boron atom is less electronegative.
So here the boron atom (B) is the center atom and the fluorine atoms (F) are the outside atoms.
Step 3: Connect each atoms by putting an electron pair between them
Now in the BF3 molecule, you have to put the electron pairs between the boron atom (B) and fluorine atoms (F).
This indicates that the boron (B) and fluorine (F) are chemically bonded with each other in a BF3 molecule.
Step 4: Make the outer atoms stable
Now in this step, you have to check the stability of the outer atoms.
Here in the sketch of BF3 molecule, you can see that the outer atoms are fluorine atoms.
These outer fluorine atoms are forming an octet and hence they are stable.
Also, in step 1 we have calculated the total number of valence electrons present in the BF3 molecule.
The BF3 molecule has a total 24 valence electrons and all these valence electrons are used in the above sketch of BF3.
Hence there are no remaining electron pairs to be kept on the central atom.
So now let’s proceed to the next step.
Step 5: Check the stability of lewis structure
Now you have come to the final step in which you have to check the stability of lewis structure of BF3.
The stability of lewis structure can be checked by using a concept of formal charge.
In short, now you have to find the formal charge on boron (B) atom as well as fluorine (F) atoms present in the BF3 molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
You can see the number of bonding electrons and nonbonding electrons for each atom of BF3 molecule in the image given below.
For Boron (B) atom:
Valence electrons = 3 (because boron is in group 13)
Bonding electrons = 6
Nonbonding electrons = 0
For Fluorine (F) atom:
Valence electron = 7 (because fluorine is in group 17)
Bonding electrons = 2
Nonbonding electrons = 6
|Formal charge||=||Valence electrons||–||(Bonding electrons)/2||–||Nonbonding electrons|
From the above calculations of formal charge, you can see that the boron (B) atom as well as fluorine (F) atom has a “zero” formal charge.
This indicates that the above lewis structure of BF3 is stable and there is no further change in the above structure of BF3.
In the above lewis dot structure of BF3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of BF3.
I hope you have completely understood all the above steps.
For more practice and better understanding, you can try other lewis structures listed below.
Try (or at least See) these lewis structures for better understanding: