SeO32- Lewis structure

SeO₃^2- (selenite) has one selenium atom and three oxygen atoms.

In the SeO₃^2- Lewis structure, there is one double bond and two single bonds around the selenium atom, with three oxygen atoms attached to it. The oxygen atom with a double bond has two lone pairs, the two oxygen atoms with single bonds have three lone pairs, and the selenium atom has one lone pair.

Also, there is a negative (-1) charge on the two oxygen atoms with single bonds.

Alternative method: Lewis structure of SeO₃^2-

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 SeO₃^2- 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

Now the SeO₃^2- has a negative (-2) charge, so we have to add two more electrons.

So the total valence electrons = 6 + 18 + 2 = 26

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

• Second, find the total electron pairs

We have a total of 26 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 = 26 ÷ 2 = 13

• 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 13 electron pairs. And three Se — O bonds are already marked. So we have to only mark the remaining ten 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 one lone pair.

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 – 2 – ½ (6) = +1

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:

Final structure

The final structure of SeO₃^2- consists of a central selenium atom connected to three oxygen atoms. In this configuration, the selenium atom maintains one lone pair and forms a single double bond with one oxygen atom and single bonds with the remaining two oxygen atoms to fulfill its expanded valence shell. The double-bonded oxygen atom retains two lone pairs, while the two single-bonded oxygen atoms each maintain three lone pairs. This layout is the most stable because it minimizes formal charges, resulting in a formal charge of zero for the selenium and the double-bonded oxygen, while the two single-bonded oxygen atoms each carry a -1 charge. As a result, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the selenite ion.

To complete the representation, draw square brackets around the entire Lewis structure and place a “2-” sign as a superscript outside the upper right bracket. This notation signifies that the negative charge is a property of the whole ion, resulting from the two additional electrons gained by the collective group of atoms.

Next: HSO₄^– Lewis structure

External video

• How to Draw the Lewis Dot Structure for SeO3 2- (Selenite ion) – YouTube • Wayne Breslyn

External links

• https://oneclass.com/homework-help/chemistry/6931740-aluminum-selenite.en.html