Ready to learn how to draw the lewis structure of AsO2- ion?
Here, I have explained 6 simple steps to draw the lewis dot structure of AsO2- ion (along with images).
So, if you are ready to go with these 6 simple steps, then let’s dive right into it!
Lewis structure of AsO2- ion contains one double bond and one single bond between the Arsenic (As) atom and Oxygen (O) atoms. The Arsenic atom (As) is at the center and it is surrounded by 2 Oxygen atoms (O). The Arsenic atom has 1 lone pair, the single bonded Oxygen atom has 3 lone pairs and the double bonded Oxygen atom has 2 lone pairs.
Let’s draw and understand this lewis dot structure step by step.
(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of AsO2- ion).
6 Steps to Draw the Lewis Structure of AsO2- ion
Step #1: Calculate the total number of valence electrons
Here, the given ion is AsO2- ion. In order to draw the lewis structure of AsO2- ion, first of all you have to find the total number of valence electrons present in the AsO2- ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).
So, let’s calculate this first.
Calculation of valence electrons in AsO2- ion
- For Arsenic:
Arsenic is a group 15 element on the periodic table.
Hence, the valence electrons present in arsenic is 5 (see below image).
- For Oxygen:
Oxygen is a group 16 element on the periodic table.
Hence, the valence electron present in oxygen is 6 (see below image).
Hence in a AsO2- ion,
Valence electrons given by Arsenic (As) atom = 5
Valence electrons given by each Oxygen (O) atom = 6
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in AsO2- ion = 5 + 6(2) + 1 = 18
Step #2: Select the center atom
While selecting the atom, always put the least electronegative atom at the center.
(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). 
Here in the AsO2 molecule, if we compare the arsenic atom (As) and oxygen atom (O), then the arsenic is less electronegative than oxygen.
So, arsenic should be placed in the center and the remaining 2 oxygen atoms will surround it.
Step #3: Put two electrons between the atoms to represent a chemical bond
Now in the above sketch of AsO2 molecule, put the two electrons (i.e electron pair) between each arsenic atom and oxygen atom to represent a chemical bond between them.
These pairs of electrons present between the Arsenic (As) and Oxygen (O) atoms form a chemical bond, which bonds the arsenic and oxygen atoms with each other in a AsO2 molecule.
Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom
Don’t worry, I’ll explain!
In the Lewis structure of AsO2, the outer atoms are oxygen atoms.
So now, you have to complete the octet on these oxygen atoms (because oxygen requires 8 electrons to have a complete outer shell).
Now, you can see in the above image that all the oxygen atoms form an octet.
Also, only 16 valence electrons of AsO2- ion are used in the above structure.
But there are total 18 valence electrons in AsO2- ion (as calculated in step #1).
So the number of electrons left to be kept on the central atom = 18 – 16 = 2.
So let’s keep these two electrons (i.e 1 electron pair) on the central atom.
Now, let’s move to the next step.
Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond
In this step, we have to check whether the central atom (i.e arsenic) has an octet or not.
In simple words, we have to check whether the central Arsenic (As) atom has 8 electrons or not.
As you can see from the above image, the central atom (i.e arsenic) has only 6 electrons. So it does not fulfill the octet rule.
Now, in order to fulfill the octet of arsenic atom, we have to move the electron pair from the outer atom (i.e oxygen atom) to form a double bond.
Now you can see from the above image that the central atom (i.e arsenic), is having 8 electrons.
So it fulfills the octet rule.
Step #6: Check the formal charge
Now, you have come to the final step and here you have to check the formal charge on AsO2 molecule.
For that, you need to remember the formula of formal charge;
Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2
- For Arsenic:
Valence electron = 5 (as it is in group 15)
Nonbonding electrons = 2
Bonding electrons = 6
- For double bonded Oxygen:
Valence electron = 6 (as it is in group 16)
Nonbonding electrons = 4
Bonding electrons = 4
- For single bonded Oxygen:
Valence electron = 6 (as it is in group 16)
Nonbonding electrons = 6
Bonding electrons = 2
|Formal charge||=||Valence electrons||–||Nonbonding electrons||–||(Bonding electrons)/2|
|Double bonded O||=||6||–||4||–||4/2||=||0|
|Single bonded O||=||6||–||6||–||2/2||=||-1|
Let’s keep these charges on the atoms in the above lewis structure of AsO2- ion.
As you can see in the above sketch, there is one -ve charge on the single bonded oxygen atom, which indicates the -1 formal charge on the AsO2 molecule.
Hence, the above lewis structure of AsO2- ion is the stable lewis structure.
Each electron pair (:) in the lewis dot structure of AsO2- ion represents the single bond ( | ). So the above lewis dot structure of AsO2- ion can also be represented as shown below.
Related lewis structures for your practice:
Lewis Structure of SBr4
Lewis Structure of BrCl5
Lewis Structure of CFCl3
Lewis Structure of NCl2-
Lewis Structure of AsCl5