Lewis structure of SeO3

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The Lewis structure of SeO₃ contains three double bonds, with selenium in the center, and three oxygens on either side. There are two lone pairs on each oxygen atom, and the selenium atom does not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of SeO₃.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability
#6 Convert lone pair and calculate formal charge again (if formal charges are not closer to zero)

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… both selenium and oxygen are the group 16 elements. Hence, both selenium and oxygen have six valence electrons.

Now SeO₃ has one selenium atom and three oxygen atoms.

So the total number of valence electrons = valence electrons of selenium atom + (valence electrons of oxygen atom × 3)

Therefore, the total number of valence electrons = 6 + 18 = 24

• Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for selenium and oxygen as follows:

Electronegativity value of selenium = 2.55
Electronegativity value of oxygen = 3.44

Obviously, selenium is less electronegative than oxygen. Hence, assume that selenium is the central atom.

So now, put selenium in the center and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of SeO₃ something like this:

Also read: How to draw Lewis structure of H₂SO₃ (5 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since selenium is surrounded by three oxygens, use six electrons to show three chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 24 valence electrons. And in the above structure, we have already used six valence electrons. Hence, eighteen valence electrons are remaining.

Two valence electrons represent one lone pair. So eighteen valence electrons = nine lone pairs.

Note that selenium is period 4 element, so it can keep more than 8 electrons in its last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are oxygens, so each oxygen will get three lone pairs. And the central atom (selenium) will not get any lone pair, because all nine lone pairs are used.

So the Lewis structure of SeO₃ looks something like this:

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (selenium) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of CCl₂F₂ (4 steps)

#4 Complete octet on central atom

Remember that selenium is a period 4 element, so it can keep more than 8 electrons in its last shell.

Now selenium already has six valence electrons. Hence, selenium needs two more valence electrons to complete its octet.

So convert one lone pair from one oxygen atom to make a new bond with the selenium atom. And then, the Lewis structure of SeO₃ looks something like this:

In the above structure, you can see that the octet is completed on the central atom (selenium), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

#5 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For selenium atom

Valence electrons = 6
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 6 – 0 – ½ (8) = +2

• For left oxygen and right oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

• For top oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of SeO₃ looks something like this:

In the above structure, you can see that the formal charges of atoms are not closer to zero. Therefore, convert lone pair and calculate formal charge again.

Also read: How to draw Lewis structure of HSO₄^– (5 steps)

#6 Convert lone pair and calculate formal charge again

As mentioned earlier, selenium is a period 4 element, so it can keep more than 8 electrons in its last shell.

So again convert one lone pair from the left oxygen atom and right oxygen atom to make a new bond with the selenium atom. And then, the Lewis structure of SeO₃ looks something like this:

Now one last thing we need to do is, calculate the formal charge again and check the stability of the above structure.

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For selenium atom

Valence electrons = 6
Nonbonding electrons = 0
Bonding electrons = 12

Formal charge = 6 – 0 – ½ (12) = 0

• For each oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of SeO₃ looks something like this:

In the above structure, you can see that the formal charges of both (selenium and oxygen) are zero. Therefore, this is the stable Lewis structure of SeO₃.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

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Related

• Lewis structure of H₂SO₃
• Lewis structure of CCl₂F₂
• Lewis structure of HSO₄^–
• Lewis structure of C₂H₂Cl₂
• Lewis structure of C₂^2-

External links

• SeO3 Lewis Structure in 6 Steps (With Images) – Pediabay
• Draw all of the Lewis structures of SeO3 that obey the octet rule – Homework.Study.com
• SeO3 Lewis Structure (Selenium Trioxide) – Pinterest
• Draw all of the Lewis structures of SeO3 which obey the octet rule – Chegg
• lewis structure of SeO3 – Brainly
• Lewis dot structure and lewis dot diagram for SeO3 – Numerade
• Draw all of the lewis structures of SeO3 which obey the octet rule – Course Hero