How to calculate formal charges of ozone (O3) 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 bonded atoms in the different resonance structures of ozone (O3) and also in its best possible Lewis structure. We will also determine the overall charge present on O3.

So for all this interesting information, continue reading!

Name of the molecule Ozone  
Chemical formulaO3
The formal charge on the central O-atom
+1
The formal charge on single bonded O-atom-1
The formal charge on double-bonded O-atom0
The overall formal charge on O30

How to calculate the formal charges on O3 atoms?

The formal charges can be calculated using the formula given below:

formal charge formula

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 the ozone Lewis structure is given below to determine the formal charges on three bonded oxygen (O) atoms in O3.

best stable lewis structure of O3

The above Lewis structure displays a total of 18 valence electrons. An oxygen (O) atom is present at the center. It is bonded to 2 other O-atoms via a single and a double covalent bond, respectively.

The central O-atom contains 1 lone pair of electrons. The single-bonded O-atom contains 3 lone pairs, while 2 lone pairs are present on the double-bonded O-atom.

Let’s find out how we can determine the formal charges present on each atom in the ozone (O3) Lewis structure.

For the central Oxygen atom

calculating formal charge on central Oxygen atom in O3

  • Valence electrons of Oxygen = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 1 double bond + 1 single bond = 1(4) + 1(2) = 6 electrons
  • Non-bonding electrons = One lone pair = 2 electrons
  • Formal charge on the central Oxygen atom = 6 – 2 – 6/2 = 6 – 2 – 3 = 6 – 5 = +1

The formal charge on the central O-atom in O3 is +1.

For double-bonded oxygen atom

calculating formal charge on double bonded Oxygen atom in O3

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

The formal charge on the double-bonded O-atom in O3 is 0.

For each single-bonded oxygen atom

calculating formal charge on single bonded Oxygen atom in O3

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

The formal charge on the single-bonded O-atom in O3 is -1.

This calculation shows that zero formal charges are present on double-bonded O-atom in O3However, a +1 and a -1 formal charge is present on the other two O-atoms.

O3 lewis structure with formal charge

 A +1 formal charge cancels with -1; therefore, the overall charge present on the molecule is zero.

O3 formal charge

The actual O3 structure is a hybrid of the following resonance structures. Each resonance structure is equivalent. It is due to the presence of formal charges on the bonded atoms that the double bond keeps shifting from one position to another to give the best possible O3 Lewis representation, as shown below.

O3 resonance structure with formal charge

You must keep in mind that a double bond cannot be formed on both sides of the central O-atom at any one time in the O3 Lewis structure.

This is because oxygen can accommodate only a total of 8 electrons in its valence shell, unlike sulfur or phosphorus atoms that have an expanded octet.

Also, check –

FAQ

How can you calculate O3 formal charges?

The formal charges present on the bonded atoms in O3  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 the central O-atom in the O3 Lewis structure?

The central oxygen (O) atom carries a +1 formal charge in O3.

What is the formal charge on double-bonded O-atom in O3?   

Zero formal charge is present on double-bonded O-atom in O3.

What is the formal charge on single-bonded O-atom in O3? 

-1 formal charge is present on single-bonded O-atom in O3.

Do all three O-atoms carry the same formal charge in O3?

No, the three O-atoms carry different, i.e.,  +1, 0 and -1 formal charges in the O3 Lewis structure.

What is the overall charge present on O3 

Zero or no formal charge is present on O3 overall. +1 formal charge of central O-atom cancels with -1 formal charge of an outer O-atom. Thus, it is a neutral molecule overall.

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 O3, a +1 formal charge is present on the central O-atom.
  • The double-bonded O-atom also has zero formal charges in O3.
  • The single-bonded O-atoms have a -1 formal charge in O3.
  • The overall formal charge on O3 is also zero as +1 cancels with -1.
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