How to calculate formal charges of water (H2O) 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 H2O and also the overall charge present on the molecule.

So, continue reading!

Name of the molecule Water
Chemical formulaH2O
The formal charge on each H-atom0
The formal charge on the O-atom0
Overall formal charge on H2O0

How to calculate the formal charges on H2O 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 H2O.

The most preferred Lewis representation of H2O is as shown below.

best stable lewis structure of H2O

The water molecule consists of a total of 8 valence electrons. An oxygen (O) atom is present at the center, which is bonded to two atoms of hydrogen (H), one on each side, via a single covalent bond.

Two lone pairs of electrons are also present at the central O-atom, while no lone pair of electrons is present on any of the two H-atoms.

It is the best possible Lewis structure of H2O 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 H2O Lewis structure.

For the central oxygen atom

calculating formal charge on oxygen atom in H2O

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

The formal charge on the O-atom in H2O is 0.

 For each hydrogen atom

calculating formal charge on hydrogen atom in H2O

  • 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 pair = 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 H2O is 0.

This calculation shows that zero formal charges are present on the central O-atom and also on both H-atoms in the H2O Lewis structure.

h2o lewis structure with formal charge

The overall formal charge present on the molecule is thus zero, as shown below. 

h2o formal charge

 

Also, check –

FAQ

How can you calculate H2O formal charges?

The formal charges present on the bonded atoms in H2O 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 O-atom in H2O?

The central Oxygen (O) atom carries zero formal charges in H2O.

What is the formal charge on H-atoms in H2O?

Zero or no formal charge is present on both H-atoms in H2O.

What is the overall formal charge on H2O?

The overall formal charge on the H2O Lewis structure is 0.

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 H2O, zero formal charges are present on the central oxygen atom.
  • Both single-bonded hydrogen atoms also have zero formal charges in H2
  • The overall formal charge on H2O is 0. It is thus a neutral molecule.
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My name is Vishal Goyal and I am the founder of Topblogtenz. I hold a degree in B.tech (Chemical Engineering) and have a strong passion for the life sciences and chemistry. As a highly qualified and experienced chemistry tutor with 4 years of experience, I possess a deep understanding of the unique challenges that students often encounter when attempting self-study in the field of chemistry. I have created this website as a comprehensive resource for those who are seeking guidance and support in their chemistry studies. I have brought together a team of experts, including experienced researchers, professors, and educators, to provide our readers with accurate and engaging information on a wide range of chemistry and science topics. Our goal is to make complex subjects like chemistry accessible and understandable for all. I hope you find the information and resources on our site helpful in your studies. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/

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