How to calculate formal charges of azide [N3]- ion 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 N3– bonded atoms in addition to the charge present on the ion overall.
So, without any further delay, let us start reading!
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 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).
The most preferred Lewis representation of N3– is as shown below.
It is the best possible Lewis structure of N3– because the formal charges are minimized in it, thus, it is also the most stable.
It is made up of three identical nitrogen (N) atoms and consists of a total of 16 valence electrons. The central N-atom is double-bonded to two other N-atoms, one on each side.
There is no lone pair of electrons on the central N-atom. However, each outer N-atom carries two lone pairs, respectively.
Now let’s calculate the formal charges present on each of the three N-atoms in the above Lewis structure using the formal charge formula.
∴ The formal charge on each outer N-atom in N3– is -1.
The above calculation shows that the central N-atom carries a +1 formal charge while each double-bonded N-atom carries a -1 formal charge, respectively. +1 + (-1) + (-1) = -1; thus, the overall charge present on the azide [N3]– ion is -1.
As a final step, the N3– Lewis structure is enclosed in square brackets, and a -1 formal charge is placed at the top right corner, as shown below.
The formal charges present on the bonded atoms in N3– 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 present on the central N-atom in N3–?
The central N-atom carries a +1 formal charge in N3– Lewis structure.
What is the formal charge present on each outer N-atom in N3–?
Each double-bonded N-atom carries a -1 formal charge in N3–.
Do all three N-atoms carry the same formal charges in N3–?
No. The central N-atom carries a +1 formal charge. Contrarily, each outer N-atom carries a -1 formal charge in N3– Lewis structure.
What is the overall charge present on N3–?
The +1 formal charge of the central N-atom cancels with the -1 formal charge of one of the two outer N-atoms. As a result, a -1 formal charge is present on N3– overall.
Summary
The best possible Lewis structure of a 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].
The central N-atom carries a +1 formal charge in the most preferred Lewis structure of N3–.
Each double-bonded O-atom carries a -1 formal charge in N3–.
+1 formal charge of the central N-atom cancels with the -1 formal charge of one of the two outer N-atoms.
This leaves behind a -1 formal charge which is also the charge present on N3– overall. Thus, the azide ion is a monovalent anion.
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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