AsO43- Lewis structure

AsO₄^3- (arsenate) has one arsenic atom and four oxygen atoms.

In the AsO₄^3- Lewis structure, there is one double bond and three single bonds around the arsenic atom, with four oxygen atoms attached to it. The oxygen atom with a double bond has two lone pairs, and the three oxygen atoms with single bonds have three lone pairs.

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

Alternative method: Lewis structure of AsO₄^3-

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 AsO₄^3- has one arsenic atom and four oxygen atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of four oxygen atoms = 6 × 4 = 24

Now the AsO₄^3- has a negative (-3) charge, so we have to add three more electrons.

So the total valence electrons = 5 + 24 + 3 = 32

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

• Second, find the total electron pairs

We have a total of 32 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 = 32 ÷ 2 = 16

• 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 16 electron pairs. And four As — O bonds are already marked. So we have to only mark the remaining twelve 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 zero lone pair because all twelve 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 arsenic atom, formal charge = 5 – 0 – ½ (8) = +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 AsO₄^3- consists of a central arsenic atom connected to four oxygen atoms. In this configuration, the arsenic atom utilizes an expanded valence shell to form one double bond and three single covalent bonds with the surrounding oxygen atoms. Within this layout, the arsenic atom and the double-bonded oxygen atom carry a formal charge of zero, while each of the three single-bonded oxygen atoms holds a -1 formal charge. Each oxygen atom fulfills its octet: the double-bonded oxygen maintains two lone pairs, and the three single-bonded oxygens each retain three lone pairs. Therefore, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the arsenate ion.

To complete the representation, draw square brackets around the entire Lewis structure and place a “3-” 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 three additional electrons within the structure.

Next: GeH₄ Lewis structure

External video

• How to Draw the Lewis Dot Structure for AsO4 3-: Arsenate ion – YouTube • Wayne Breslyn

External links

• https://www.chemistryscl.com/general/Arsenate-ion-lewis-structure/
• https://oneclass.com/homework-help/chemistry/7028160-aso4-3-lewis-structure.en.html