SeO3 Lewis structure

SeO₃ (selenium trioxide) has one selenium atom and three oxygen atoms.

In the SeO₃ Lewis structure, there are three double bonds around the selenium atom, with three oxygen atoms attached to it, on each oxygen atom, there are two lone pairs.

Alternative method: Lewis structure of SeO₃

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, both selenium and oxygen lie in group 16.

Hence, both selenium and oxygen have six valence electrons.

Since SeO₃ has one selenium atom and three oxygen atoms, so…

Valence electrons of one selenium atom = 6 × 1 = 6
Valence electrons of three oxygen atoms = 6 × 3 = 18

And the total valence electrons = 6 + 18 = 24

Learn how to find: Selenium valence electrons and Oxygen valence electrons

• Second, find the total electron pairs

We have a total of 24 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 24 ÷ 2 = 12

• Third, determine the central atom

We have to place the least electronegative atom at the center.

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

Therefore, place selenium in the center and oxygens on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 12 electron pairs. And three Se — O bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that selenium is a 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.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygens.

So for each oxygen, there are three lone pairs, and for selenium, there is zero lone pair because all nine electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

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

For selenium atom, formal charge = 6 – 0 – ½ (6) = +3

For each oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

Here, both selenium and oxygen atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both selenium and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the oxygen atom to make a new Se — O bond with the selenium atom as follows:

Since there are charges on selenium and oxygen atoms, again convert a lone pair of the oxygen atom to make a new Se — O bond with the selenium atom as follows:

There are still charges on selenium and oxygen atoms, so again convert a lone pair of the oxygen atom to make a new Se — O bond with the selenium atom as follows:

Final structure

The final structure of SeO₃ has a central selenium atom connected to three oxygen atoms through double covalent bonds. In this arrangement, the selenium atom utilizes an expanded valence shell to accommodate twelve electrons, while each oxygen atom satisfies the octet rule by retaining two lone pairs alongside its double bond. This configuration is the most stable because it results in a formal charge of zero for the selenium atom and all three oxygen atoms, representing the most energetically favorable state for the molecule. Therefore, this specific electronic distribution serves as the definitive and most accurate Lewis representation of selenium trioxide.

Next: SeO₃^2- Lewis structure

External links

• https://lambdageeks.com/seo3-lewis-structure/
• https://www.coursehero.com/tutors-problems/Chemistry/7654365-lewis-dot-structure-for-SeO3/