How to calculate formal charges of ammonia [NH3] with lewis structure?
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 NH3 and also the overall charge present on the molecule.
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 to calculate the formal charges in the most preferred Lewis structure of NH3.
The most preferred Lewis representation of NH3 is as shown below.
It consists of a total of 8 valence electrons. A Nitrogen (N) atom is present at the center, which is bonded to three atoms of Hydrogen (H) at the sides via single covalent bonds.
One lone pair of electrons is present at the central N-atom, while no lone pairs of electrons are present on any of the three H-atoms.
It is the best possible Lewis structure of NH3 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 NH3 Lewis structure.
Formal charge on the Nitrogen atom = 5 – 2 – 6/2 = 5 – 2 – 3 = 5 – 5 = 0
∴ The formal charge on the N-atom in NH3 is 0.
For each hydrogen atom
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 NH3 is 0.
This calculation shows that zero formal charges are present on each of the three H-atoms as well as on the central nitrogen atom in the NH3 Lewis structure, as shown below.
Consequently, no overall charge is present on the NH3 Lewis structure, denoting that it’s a neutral molecule.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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