# How to calculate formal charges of chlorate [ClO3]- ion with lewis structure?

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In covalently bonded molecules, formal charge is the charge assigned to an atom based on the assumption that the bonded electrons are equally shared between concerning atoms, regardless of their electronegativity.

The overall formal charge present on a molecule is a measure of its stability.

The fewer the formal charges present on the bonded atoms in a molecule (close to zero), the greater the stability of its Lewis structure.

In this article, we will calculate the formal charges present on the bonded atoms in ClO3 and also the overall charge present on the molecular ion.

 Name of the molecular ion Chlorate Chemical formula [ClO3]– The formal charge on the Cl atom 0 The formal charge on double-bonded O-atoms 0 The formal charge on single bonded O-atom -1 The overall formal charge on ClO3– -1

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## How to calculate the formal charges on ClO3– atoms?

The formal charges can be calculated using the formula given below: The formal charge of an atom = [valence electrons of an atom – non-bonding electrons – ½ (bonding electrons)]

• The valence electrons (V.E) of an atom are the total number of electrons present in its valence shell. Valence electrons can be determined by locating the position of the elemental atom in the Periodic Table.
• Non-bonding electrons (N.E) are the number of lone pairs present on the atom. (1 lone pair means 2 nonbonding electrons).
• Bonding electrons (B.E) are the total electrons shared with the atom via covalent chemical bonds. (1 single bond means 2 bonding electrons).

Now let us use this formula and calculate the formal charges in the most preferred ClO3 structure.

The most preferred Lewis structure of ClO3 is as shown below. It consists of a total of 26 valence electrons. A chlorine (Cl) atom is present at the center, which is bonded to two atoms of oxygen (O) via double covalent bonds and another oxygen atom via a single covalent bond.

One lone pair of electrons is present at the central Cl-atom. Each of the two double-bonded O-atoms contains 2 lone pairs, while the single-bonded O-atom contains 3 lone pairs, respectively.

It is the best possible Lewis structure of ClO3 because the formal charges are minimized in it, and thus, it is the most stable.

Let’s find out how we can determine the formal charges present on each atom in the above ClO3 Lewis structure.

For the central chlorine atom • Valence electrons of chlorine = It is present in Group VII A = 7 valence electrons
• Bonding electrons around chlorine = 1 single bond + 2 double bonds = 2 + 2(4) = 10 electrons
• Non-bonding electrons on chlorine = 1 lone pair = 2 electrons
• Formal charge on Cl atom = 7 – 2 – 10/2 = 7 – 2 – 5 = 7 – 7 = 0

∴ The formal charge on the Cl atom in ClO3 is 0.

For single-bonded oxygen atom • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
• Bonding electrons around oxygen = 1 single bond = 2 electrons
• Non-bonding electrons on oxygen = 3 lone pairs = 3(2) = 6 electrons
• Formal charge on O atom = 6 – 6 – 2/2 = 6 – 6 – 1 = 6 – 7 = -1

∴ The formal charge on the Single bonded oxygen (O) atom in ClO3 is -1.

For double-bonded oxygen atoms • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
• Bonding electrons around oxygen = 1 double bond = 4 electrons
• Non-bonding electrons on oxygen = 2 lone pairs = 2(2) = 4 electrons
• Formal charge on oxygen atom = 6 – 4 – 4/2 = 6 – 4 – 2 = 6 – 6 = 0

∴ The formal charge on the Double bonded oxygen (O) atom in ClO3 is 0.

This calculation shows zero formal charges are present on the central Cl atom and two double-bonded O-atoms, while the single-bonded O-atom carries a -1 formal charge, which is also the charge present on the ClO3 ion overall, as shown below. Finally, the ClO3 Lewis structure is enclosed in square brackets, and a -1 charge is placed at the top right corner. Also, check –

## FAQ

### How can you calculate ClO3– formal charges?

The formal charges present on the bonded atoms in ClO3  can be calculated using the formula given below:

V.E – N.E – B.E/2

Where –

⇒ V.E = valence electrons of an atom

⇒ N.E = non-bonding electrons, i.e., lone pairs

⇒ B.E = bonding electrons

### What is the formal charge on Cl-atom in ClO3–?

The central chlorine (Cl) atom carries zero formal charges in ClO3.

### What is the formal charge on O-atoms in ClO3–?

Zero or no formal charge is present on Cl=O bonded oxygen atoms in ClO3 while -1 formal charge is present on Cl-O bonded oxygen atoms in ClO3.

### Do all three O-atoms carry the same formal charge in ClO3–?

No, the single bonded O-atom carries a -1 formal charge, while no formal charge is present on the double bonded O-atoms in ClO3.

### What is the overall formal charge on ClO3–?

The overall formal charge on ClO3 is -1.

## Summary

• The best possible Lewis structure of a molecule is the one in which the bonded atoms carry formal charges as close to zero as possible.
• The formal charge formula is [ V.E – N.E – B.E/2].
• In ClO3, zero formal charges is present on the central Cl-atom.
• The double-bonded O-atoms also have zero formal charges in ClO3.
• The single-bonded O-atom has a -1 formal charge in ClO3.
• The overall formal charge on ClO3 is -1.
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