How to calculate formal charges of ammonium [NH4]+ 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 [NH4]+ Lewis structure and also the overall charge present on the molecular ion.

So, for all this interesting information, continue reading!

Name of the molecular ion Ammonium
Chemical formula [NH4]+
The formal charge on the N-atom+1
The formal charge on each H-atom0
The overall formal charge on  [NH4]++1

How to calculate the formal charges on NH4+ 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 [NH4]+.

The most preferred Lewis representation of [NH4]+ is as shown below.

best stable lewis structure of NH4+

It consists of a total of 8 valence electrons. A Nitrogen (N) atom is present at the center, which is bonded to four atoms of Hydrogen (H), one on each side, via a single covalent bond respectively.

No pair of electrons is present at the central N-atom and on any of the four H-atoms.

It is the best possible Lewis structure of [NH4]+ 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 [NH4]+ Lewis structure.

For the central nitrogen atom

calculating formal charge on nitrogen atom in NH4+

  • Valence electrons of nitrogen = It is present in Group VA = 5 valence electrons
  • Bonding electrons = 4 single bonds = 4 (2) = 8 electrons
  • Non-bonding electrons = no lone pair = 0 electrons
  • Formal charge on the Nitrogen atom = 5 – 0 – 8/2 = 5 – 0 – 4 = 5 – 4 = +1

The formal charge on the N-atom in [NH4]+ is +1.

 For each hydrogen atom

calculating formal charge on hydrogen atom in NH4+

  • 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 [NH4]+ is 0.

This calculation shows zero formal charges are present on each of the four H-atoms while a  +1 formal charge on the central nitrogen atom, which is also the overall formal charge present on the ammonium [NH4]+ ion, as shown below. 

NH4+ lewis structure with formal charge

The NH4+ Lewis structure is finally enclosed in square brackets, and a -1 formal charge is placed at the top right corner.

NH4+ formal charge

 

Also, check –

FAQ

How can you calculate NH4+ formal charges?

The formal charges present on the bonded atoms in NH4+ 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 central N-atom in [NH4]+?

The central nitrogen (N) atom carries +1 formal charge in [NH4]+.

What is the formal charge on H-atoms in [NH4]+?

Zero or no formal charges are present on H-atoms in [NH4]+.

Do all of the hydrogen atoms carry the same formal charge in [NH4]+?

Yes, all four hydrogen atoms are single covalent bonded and carry zero formal charges in [NH4]+ Lewis structure.

What is the overall formal charge on [NH4]+?

The overall formal charge on [NH4]+ 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 [NH4]+, a +1 formal charge is present on the central nitrogen atom.
  • In [NH4]+, all four single-bonded hydrogen atoms carry zero or no formal charges.
  • The overall formal charge on NH4+ is +1; hence it is a monovalent cation.
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