AsO33- Lewis structure

AsO₃^3- has one arsenic atom and three oxygen atoms.

In AsO₃^3- Lewis structure, there are three single bonds around the arsenic atom, with three oxygen atoms attached to it. Each oxygen atom has three lone pairs, and the arsenic atom has one lone pair.

Also, there is a negative (-1) charge on each oxygen atom.

Alternative method: Lewis structure of AsO₃^3-

Contents

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 AsO₃^3- has one arsenic atom and three oxygen atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of three oxygen atoms = 6 × 3 = 18

Now the AsO₃^3- has a negative (-3) charge, so we have to add three more electrons.

So the total valence electrons = 5 + 18 + 3 = 26

Learn how to find: Arsenic 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 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

AsO33- Lewis Structure (Step 1) — Rough sketch of AsO₃^3- Lewis structure | Image: Learnool

Lone pair

Here, we have a total of 13 electron pairs. And three As — 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 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:

AsO33- Lewis Structure (Step 2) — Lone pairs marked on AsO₃^3- Lewis structure | Image: Learnool

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 (6) = 0

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

Here, each oxygen atom has a charge, so mark it on the sketch as follows:

AsO33- Lewis Structure (Step 3) — Formal charges marked, and got the most stable Lewis structure of AsO₃^3- | Image: Learnool

Final structure

AsO33- Lewis Structure (Final) — AsO₃^3- Lewis structure showing a negative (-3) charge | Image: Learnool

The final structure of AsO₃^3- features a central arsenic atom connected to three oxygen atoms through single covalent bonds. In this layout, the arsenic atom satisfies the octet rule by maintaining one lone pair alongside its three bonding pairs. Each oxygen atom fulfills its octet by retaining three lone pairs of its own in addition to the single shared bond. This configuration is the most stable because it optimizes the formal charge distribution; the arsenic atom carries a formal charge of zero, while each of the three oxygen atoms carries a formal charge of -1, resulting in the overall 3- charge. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the AsO₃^3- ion.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 3- is then written as a superscript outside the brackets at the top right, indicating that the structure possesses three additional electrons compared to the neutral atoms.

Next: C₄H₆ Lewis structure

External video

AsO3 3- Lewis Structure: How to Draw the Lewis Structure for AsO3 3- – YouTube • Wayne Breslyn

External links

Deep

Learnool.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.