How to calculate formal charges of carbon monoxide (CO) 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 CO and also the overall charge present on the molecule.

So, continue reading!

Name of the molecule Carbon monoxide
Chemical formulaCO
The formal charge on the C atom-1
The formal charge on the O-atom+1
The overall formal charge on CO0

How to calculate the formal charges on CO 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 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 carbon monoxide, i.e., CO.

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

stable lewis structure of CO

It consists of a total of 10 valence electrons. The molecule consists of only two atoms; one carbon (C) atom, which is bonded to one atom of oxygen (O) via a triple covalent bond.

One lone pair of electrons is present on the C-atom and also on the O-atom.

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

For carbon atom

calculating formal charge on the Carbon atom in CO

  • Valence electrons of carbon = It is present in Group IV A = 4 valence electrons
  • Bonding electrons = 1 triple covalent bond = 3(2) = 6 electrons
  • Non-bonding electrons = 1 lone pair = 2 electrons
  • Formal charge on the Carbon atom = 4 – 2 – 6/2 = 4 – 2 – 3 = 4– 5= -1

The formal charge on the C-atom in CO is -1.

 For oxygen atom

calculating formal charge on the Oxygen atom in CO

  • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 1 triple bond = 3(2) = 6 electrons
  • Non-bonding electrons = 1 lone pair = 2 electrons
  • Formal charge on the Oxygen atom = 6 – 2 – 6/2 = 6 – 2 – 3 = 6 – 5 = +1

The formal charge on the double-bonded oxygen (O) atom in CO is +1.

The above calculation shows that a -1 formal charge is present on the C-atom while a +1 formal charge is present on the O-atom in CO Lewis structure, as shown below. 

CO lewis structure with formal charge

When both formal charges are added up [(-1) +(+1) = 0], it results in a zero formal charge overall. Consequently, there is no overall formal charge on the CO Lewis structure denoting carbon monoxide is a neutral molecule.

CO formal charge

Also, check –

FAQ

How can you calculate CO formal charges?

The formal charges present on the bonded atoms in CO 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 C-atom in CO?

The central carbon (C) atom carries a -1 formal charge in CO.

What is the formal charge on O-atom in CO?

+1 formal charge is present on the oxygen O-atom in CO.

What is the formal charge of carbon in carbon monoxide (CO) when drawn with a triple bond?

The carbon (C) atom, when drawn with a triple covalent bond, carries a -1 formal charge in the CO molecule.

What is the overall formal charge on CO?

The overall formal charge on CO 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 CO, a -1 formal charge is present on the C-atom.
  • The triple-bonded O-atom has a +1 formal charge in CO.
  • The overall formal charge on CO is 0. Thus, it is a neutral molecule.
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