How to calculate formal charges of Sulfur Trioxide (SO3) 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.
Sulfur Trioxide is a colorless liquid and, upon air exposure, can “magically” produce white fumes (by reacting to moisture).
In this article, we will calculate the formal charges present on the bonded atoms in SO3 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 SO3.
The most preferred Lewis representation of the sulfur trioxide (SO3) molecule is as shown below.
It consists of a total of 24 valence electrons. A Sulfur (S) atom is present at the center, which is bonded to three atoms of oxygen (O) via three double covalent bonds.
No lone pair of electrons is present at the central S-atom. Each of the three double-bonded O-atoms contains 2 lone pairs.
It is the best possible Lewis structure of SO3 because the formal charges are minimized in it, and thus, it is also the most stable.
Let’s find out how we can determine the formal charges present on each atom in the SO3 Lewis structure.
Formal charge on the Oxygen atom = 6 – 4 – 4/2 = 6 – 4 – 2 = 6 – 6 = 0
∴ The formal charge on each double-bonded oxygen (O) atom in SO3 is 0.
This calculation shows that zero formal charges are present on the central S atom as well as on each of the three double-bonded O-atoms in the SO3 Lewis structure.
As a result, there is no overall charge on the SO3 molecule, and thus it is 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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