How to calculate formal charges of hydronium [H3O]+ 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 the [H3O]+ Lewis structure and also the overall charge present on the molecular ion.

 So, continue reading!

Name of the molecular ion Hydronium
Chemical formulaH3O+
The formal charge on each H-atom0
The formal charge on the O-atom+1
The overall formal charge on [H3O]++1

How to calculate the formal charges on H3O+ 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 calculated 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 to calculate the formal charges in the most preferred Lewis structure of [H3O]+.

The most preferred Lewis representation of the hydronium [H3O]+ ion is as shown below.

most stable H3O+ lewis structure

It consists of a total of 8 valence electrons. An Oxygen (O) atom is present at the center, which is bonded to three atoms of Hydrogen (H) at the sides, each via a single covalent bond.

One lone pair of electrons is situated at the central O-atom, while no lone pair of electrons are present on any of the three single-bonded H-atoms.

It is the best possible Lewis structure of [H3O]+ 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 [H3O]+ Lewis structure.

For the central oxygen atom

calculating formal charge on Oxygen atom in H3O+

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

The formal charge on the O-atom in [H3O]+ is +1.

For each hydrogen atom

calculating formal charge on Hydrogen atom in H3O+

  • Valence electrons of hydrogen = It is present in Group I A = 1 valence electron
  • Bonding electrons = 1 single bond = 2 electrons
  • Non-bonding electrons = no lone pairs = 0 electrons
  • Formal charge on the Hydrogen atom = 1 – 0 – 2/2 = 1 – 0 – 1 = 1 – 1 = 0

The formal charge on each H-atom in [H3O] + is 0.

This calculation shows that zero formal charges are present on each of the three H-atoms while a +1 formal charge is present on the central oxygen atom in the H3O+ Lewis structure, which is also the overall formal charge present on the [H3O] + ion, as shown below. 

H3O+ lewis structure with formal charge

As a final step, the H3O+ Lewis structure is enclosed in square brackets, and a +1 formal charge is placed at the top right corner.

H3O+ formal charge

Also, check –

FAQ

How can you calculate H3O+ formal charges?

The formal charges present on the bonded atoms in H3O+ 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

In the Lewis structure of [H3O]+, what is the formal charge on O-atom?

The central Oxygen (O) atom carries a +1 formal charge in [H3O]+ Lewis structure.

What is the formal charge on H-atoms in [H3O]+?

Zero or no formal charge is present on either of the three single-bonded H-atoms in [H3O]+.

Do all of the hydrogen atoms carry the same formal charge in [H3O]+?

Yes, all hydrogen atoms carry zero formal charges in [H3O]+.

What is the overall formal charge on [H3O]+?

The overall formal charge on [H3O]+ is +1.

Summary

  • The best possible Lewis structure of a molecule or molecular ion 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 [H3O] +, +1 formal charge is present on the central oxygen atom.
  • In [H3O] +, the hydrogen atoms carry zero or no formal charges.
  • The overall formal charge on [H3O]+ is +1.
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