What is the Lewis structure for SeO2

So you have seen the above image by now, right?

Let me explain the above image in short.

SeO2 lewis structure has a Selenium atom (Se) at the center which is surrounded by two Oxygen atoms (O). There are 2 double bonds between the Selenium atom (Se) and each Oxygen atom (O). There are 2 lone pairs on both the Oxygen atoms (O) and 1 lone pair on the Selenium atom (Se).

If you haven’t understood anything from the above image of SeO2 (selenium dioxide) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of SeO2.

So let’s move to the steps of drawing the lewis structure of SeO2.

Steps of drawing SeO2 lewis structure

Step 1: Find the total valence electrons in SeO2 molecule

In order to find the total valence electrons in a SeO2 (selenium dioxide) molecule, first of all you should know the valence electrons present in selenium 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 selenium as well as oxygen using a periodic table.

Total valence electrons in SeO2 molecule

→ Valence electrons given by selenium atom:

Selenium is a group 16 element on the periodic table. Hence the valence electrons present in selenium is 6.

You can see the 6 valence electrons present in the selenium atom as shown in the above image.

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

Hence, 

Total valence electrons in SeO2 molecule = valence electrons given by 1 selenium atom + valence electrons given by 2 oxygen atoms = 6 + 6(2) = 18.

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 SeO2 (selenium dioxide) and it contains selenium atom (Se) and oxygen atoms (O).

You can see the electronegativity values of selenium atom (Se) and oxygen atom (O) in the above periodic table.

If we compare the electronegativity values of selenium (Se) and oxygen (O) then the selenium atom is less electronegative.

So here the selenium atom (Se) 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 SeO2 molecule, you have to put the electron pairs between the selenium atom (Se) and oxygen atoms (O).

This indicates that the selenium (Se) and oxygen (O) are chemically bonded with each other in a SeO2 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 SeO2 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 SeO2 molecule.

The SeO2 molecule has a total 18 valence electrons and out of these, only 16 valence electrons are used in the above sketch.

So the number of electrons which are left = 18 – 16 = 2.

You have to put these 2 electrons on the central selenium atom in the above sketch of SeO2 molecule.

Now let’s proceed to the next step.

Step 5: Check the octet on the central atom. If it does not have octet, then shift the lone pair to form a double bond or triple bond.

In this step, you have to check whether the central selenium atom (Se) is stable or not.

In order to check the stability of the central selenium (Se) atom, we have to check whether it is forming an octet or not.

Unfortunately, the selenium atom is not forming an octet here. Selenium has only 6 electrons and it is unstable.

Now to make this selenium atom stable, you have to shift the electron pair from the outer oxygen atom so that the selenium atom can have 8 electrons (i.e octet).

After shifting this electron pair, the central selenium atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that the selenium atom is forming an octet as it has 8 electrons.

Now let’s proceed to the final step to check whether the lewis structure of SeO2 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 SeO2.

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 selenium (Se) atom as well as oxygen (O) atoms present in the SeO2 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 SeO2 molecule in the image given below.

For Selenium (Se) atom:
Valence electrons = 6 (because selenium is in group 16)
Bonding electrons = 6
Nonbonding electrons = 2

For double bonded Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

For single bonded 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 selenium (Se) atom has +1 charge and the single bonded oxygen (O) atom has -1 charge.

Because of this reason, the above obtained lewis structure of SeO2 is not stable. 

So we have to minimize these charges by shifting the electron pairs towards the selenium atom.

After shifting the electron pair from oxygen atom to selenium atom, the lewis structure of SeO2 becomes more stable.

In the above lewis dot structure of SeO2, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of SeO2.

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: