So you have seen the above image by now, right?
Let me explain the above image in short.
PF2- lewis structure has a Phosphorus atom (P) at the center which is surrounded by two Fluorine atoms (F). There is a single bond between the Phosphorus atom (P) and each Fluorine atom (F). There is a -1 formal charge on the Phosphorus atom (P).
If you haven’t understood anything from the above image of PF2- lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of PF2- ion.
So let’s move to the steps of drawing the lewis structure of PF2- ion.
Steps of drawing PF2- lewis structure
Step 1: Find the total valence electrons in PF2- ion
In order to find the total valence electrons in PF2- ion, first of all you should know the valence electrons present in the phosphorus 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 phosphorus as well as fluorine using a periodic table.
Total valence electrons in PF2- ion
→ Valence electrons given by phosphorus atom:
Phosphorus is group 15 element on the periodic table.  Hence the valence electrons present in phosphorus is 5.
You can see the 5 valence electrons present in the phosphorus 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 PF2- ion = valence electrons given by 1 phosphorus atom + valence electrons given by 2 fluorine atoms + 1 more electron is added due to 1 negative charge = 5 + 7(2) + 1 = 20.
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 ion is PF2- ion and it contains phosphorus atom (P) and fluorine atoms (F).
You can see the electronegativity values of phosphorus atom (P) and fluorine atom (F) in the above periodic table.
If we compare the electronegativity values of phosphorus (P) and fluorine (F) then the phosphorus atom is less electronegative.
So here the phosphorus atom (P) 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 PF2 molecule, you have to put the electron pairs between the phosphorus atom (P) and fluorine atoms (F).
This indicates that the phosphorus (P) and fluorine (F) are chemically bonded with each other in a PF2 molecule.
Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.
Now in this step, you have to check the stability of the outer atoms.
Here in the sketch of PF2 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 PF2- ion.
The PF2- ion has a total 20 valence electrons and out of these, only 16 valence electrons are used in the above sketch.
So the number of electrons which are left = 20 – 16 = 4.
You have to put these 4 electrons on the central phosphorus atom in the above sketch of PF2 molecule.
Now let’s proceed to the next step.
Step 5: Check the octet on the central atom
In this step, you have to check whether the central phosphorus atom (P) is stable or not.
In order to check the stability of the central phosphorus (P) atom, we have to check whether it is forming an octet or not.
You can see from the above picture that the phosphorus atom is forming an octet. That means it has 8 electrons.
And hence the central phosphorus atom is stable.
Now let’s proceed to the final step to check whether the above lewis structure is stable or not.
Step 6: 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 PF2.
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 the phosphorus atom (P) as well as fluorine atoms (F) present in the PF2 molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
For Phosphorus (P) atom:
Valence electrons = 5 (because phosphorus is in group 15)
Bonding electrons = 4
Nonbonding electrons = 4
For Fluorine (F) atom:
Valence electrons = 7 (because fluorine is in group 17)
Bonding electrons = 2
Nonbonding electrons = 6
From the above calculations of formal charge, you can see that the phosphorus (P) atom has -1 charge and the fluorine atoms have 0 charges.
So let’s keep these charges on the respective atoms in the PF2 molecule.
This overall -1 charge on the PF2 molecule is represented in the image given below.
In the above lewis dot structure of PF2- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of PF2- ion.
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:
|SI4 Lewis Structure
|GaCl3 Lewis Structure
|NSF Lewis Structure
|C2H4Br2 Lewis Structure
|CO2 lewis structure
|SO2 lewis structure
Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.
Read more about our Editorial process.