AsO2- Lewis structure

AsO₂^– has one arsenic atom and two oxygen atoms.

In AsO₂^– Lewis structure, there is one single bond and one double bond around the arsenic atom, with two oxygen atoms attached to it. The oxygen atom with a single bond has three lone pairs, the oxygen atom with a double bond has two lone pairs, and the arsenic atom has one lone pair.

Also, there is a negative (-1) charge on the oxygen atom with a single bond.

Alternative method: Lewis structure of AsO₂^–

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, arsenic lies in group 15, and oxygen lies in group 16.

Hence, arsenic has five valence electrons and oxygen has six valence electrons.

Since AsO₂^– has one arsenic atom and two oxygen atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of two oxygen atoms = 6 × 2 = 12

Now the AsO₂^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 5 + 12 + 1 = 18

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

• Second, find the total electron pairs

We have a total of 18 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 = 18 ÷ 2 = 9

• Third, determine the central atom

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

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

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

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 9 electron pairs. And two As — O bonds are already marked. So we have to only mark the remaining seven electron pairs as lone pairs on the sketch.

Also remember that arsenic 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 arsenic, 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 arsenic atom, formal charge = 5 – 2 – ½ (4) = +1

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

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

The above structure is not a stable Lewis structure because both arsenic 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 As — O bond with the arsenic atom as follows:

Final structure

The final structure of AsO₂^– features a central arsenic atom linked to two oxygen atoms. In this configuration, the arsenic atom forms a double covalent bond with one oxygen atom and a single covalent bond with the other, while retaining one lone pair. Within this layout, both oxygen atoms fulfill the octet rule: the double-bonded oxygen maintains two lone pairs, and the single-bonded oxygen maintains three lone pairs. The arsenic atom also satisfies the octet rule with its three bonding pairs and one lone pair. This arrangement is the most stable because the negative formal charge is located on an oxygen atom, which has a higher electronegativity than arsenic, while the other atoms maintain a formal charge of zero. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of AsO₂^–.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 1- is then written as a superscript outside the brackets at the top right, indicating that the structure possesses one additional electron beyond the valence count of the neutral atoms.

Next: SBr₄ Lewis structure

External video

• How to Draw the Lewis Dot Structure for AsO2 – – YouTube • Wayne Breslyn

External links

• https://www.chegg.com/homework-help/questions-and-answers/total-number-valence-electrons-lewis-structure-aso2-draw-thew-lewish-structure-aso2-q12959499
• https://study.com/academy/answer/what-is-the-total-number-of-valence-electrons-in-the-lewis-structure-of-aso2.html