What is the Charge on CO3 (Carbonate ion)? And Why?

The Charge of CO3 (Carbonate ion) is 2-.

But the question is how can you find the charge on CO3 (Carbonate ion)?

Well there are 2 methods by which you can find the charge of CO3.

Lets dive right into these methods one by one.

If you are a visual learner like me, then here is a short one minute video for you.

Method 1: By looking at what it is bonded to

The charge of CO3 (Carbonate ion) can be found out by looking at what it is bonded to.

So let’s take some examples of compounds that contain CO₃; like Na₂CO₃, K₂CO₃, etc.

Example 1: Na₂CO₃
In Na₂CO₃, the CO₃ is bonded to Sodium (Na).
You know that the ionic charge of Na is 1+.
So you can easily say that the charge of CO₃ should be 2-, then only it will get canceled out.
Hence the charge of CO₃ in Na₂CO₃ is 2-.

Example 2: K₂CO₃
In K₂CO₃, the NO₃ is bonded to Potassium (K).
And again, you know that the ionic charge of K is 1+.
So here also you can easily say that the charge of CO₃ should be 2-, then only it will get canceled out.
Hence the charge of CO₃ in K₂CO₃ is 2-.

As seen from the above examples,
The charge of CO3 is 2-.

In this way, you can easily find the charge of CO3 by looking at what it is bonded to.

Method 2: By calculating the formal charge using lewis structure

In order to calculate the formal charge on CO3 (Carbonate ion), you should know the Lewis dot structure of CO3 (Carbonate ion).

Here is the lewis structure of CO3.

Now using the above lewis structure of CO3, you have to find the formal charge on each atom that is present in the CO3 molecule.

For calculating the formal charge, you need to remember this formula;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

You can see the bonding and nonbonding electrons of CO3 from the image given below.

So now let’s calculate the formal charge on each individual atom present in CO3.

Formal charge on Carbon atom:
Valence electrons = 4 (as it is in group 14 on periodic table) ^[1]
Nonbonding electrons = 0
Bonding electrons = 8

So according to the formula of formal charge, you will get;

Formal charge on Carbon = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 4 – 0 – (8/2) = 0

So the formal charge on carbon atom is 0.

Formal charge on double bonded Oxygen:
Valence electron = 6 (as it is in group 16 on periodic table) ^[2]
Nonbonding electrons = 4
Bonding electrons = 4

So according to the formula of formal charge, you will get;

Formal charge on double bonded Oxygen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 6 – 4 – (4/2) = 0

So the formal charge on double bonded oxygen atom is 0.

Formal charge on single bonded Oxygen:
Valence electron = 6 (as it is in group 16 on periodic table)
Nonbonding electrons = 6
Bonding electrons = 2

So according to the formula of formal charge, you will get;

Formal charge on single bonded Oxygen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 6 – 6 – (2/2) = 1-

So the formal charge on single bonded oxygen atom is 1-.

Now let’s put all these charges on the lewis dot structure of CO3.

So there is overall 2- charge left on the entire molecule.

This indicates that the CO3 (Carbonate ion) has 2- charge.

I hope you have understood the above calculations of CO3 (Carbonate ion). But for your tests, you don’t need to remember the entire calculations. You should just try to remember that CO3 has 2- charge.

Check out some other related topics for your practice.

Related topics:
Charge of Beryllium (Be)
Charge of Sulfur (S)
Charge on PO4 (Phosphate ion)
Charge of Silver (Ag)
Charge of Zinc (Zn)