So you have seen the above image by now, right?
Let me explain the above image in short.
SO4 2- lewis structure has a Sulfur atom (S) at the center which is surrounded by four Oxygen atoms (O). There are 2 single bonds and 2 double bonds between the Sulfur atom (S) and each Oxygen atom (O). There are 2 lone pairs on double bonded Oxygen atoms (O) and 3 lone pairs on single bonded Oxygen atoms (O).
If you haven’t understood anything from the above image of SO4 2- lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of SO42- ion.
So let’s move to the steps of drawing the lewis structure of SO42- ion.
Steps of drawing SO4 2- lewis structure
Step 1: Find the total valence electrons in SO4 2- ion
In order to find the total valence electrons in SO4 2- ion, first of all you should know the valence electrons present in sulfur atom as well as oxygen 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 sulfur as well as oxygen using a periodic table.
Total valence electrons in SO4 2- ion
→ Valence electrons given by sulfur atom:
You can see the 6 valence electrons present in the sulfur atom as shown in the above image.
→ Valence electrons given by oxygen atom:
You can see the 6 valence electrons present in the oxygen atom as shown in the above image.
Total valence electrons in SO42- ion = valence electrons given by 1 sulfur atom + valence electrons given by 4 oxygen atoms + 2 more electrons are added due to 2 negative charges = 6 + 6(4) + 2 = 32.
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 SO4 2- ion and it contains sulfur atom (S) and oxygen atoms (O).
You can see the electronegativity values of sulfur atom (S) and oxygen atom (O) in the above periodic table.
If we compare the electronegativity values of sulfur (S) and oxygen (O) then the sulfur atom is less electronegative.
So here the sulfur atom (S) is the center atom and the oxygen atoms (O) are the outside atoms.
Step 3: Connect each atoms by putting an electron pair between them
Now in the SO4 molecule, you have to put the electron pairs between the sulfur atom (S) and oxygen atoms (O).
This indicates that the sulfur (S) and oxygen (O) are chemically bonded with each other in a SO4 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 SO4 molecule, you can see that the outer atoms are oxygen atoms.
These outer oxygen 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 SO42- ion.
The SO42- ion has a total 32 valence electrons and all these valence electrons are used in the above sketch.
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 SO42- ion.
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 sulfur (S) atom as well as oxygen (O) atoms present in the SO4 molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
For Sulfur (S) atom:
Valence electrons = 6 (because sulfur is in group 16)
Bonding electrons = 8
Nonbonding electrons = 0
For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6
From the above calculations of formal charge, you can see that the sulfur (S) atom has +2 charge while all the oxygen atoms have -1 charge.
So let’s keep these charges on the respective atoms of the SO4 molecule.
The above image shows that the lewis structure of SO4 is not stable.
So we have to minimize these charges by shifting the electron pair from the oxygen atom to the sulfur atom.
After shifting the electron pair from the oxygen atom to the sulfur atom, the charges on sulfur and two oxygen atoms become zero. And this is a more stable lewis structure. (see below image).
There are two -ve charges left on the oxygen atoms, which gives -2 formal charge on the SO4 molecule.
This overall -2 charge on the SO4 molecule is represented in the image given below.
In the above lewis dot structure of SO4 2- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of SO4 2- 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:
|ClO2 Lewis Structure
|Br2 Lewis Structure
|BeCl2 Lewis Structure
|CH3COO- Lewis Structure
|Acetone (C3H6O) Lewis Structure
|POCl3 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.
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