What is the Charge on HCN? And Why?

The Charge of HCN is 0.

But the question is how can you say that the charge on HCN (hydrogen cyanide) is 0?

Well you can say this by calculating its formal charge.

So let’s calculate the formal charge of HCN (hydrogen cyanide).

If you are a visual learner like me, then here is a short two minute video for you.

Calculating the formal charge of HCN using lewis structure

In order to calculate the formal charge on HCN (hydrogen cyanide), you should know the Lewis dot structure of HCN (hydrogen cyanide).

Here is the lewis structure of HCN.

Now using the above lewis structure of HCN, you have to find the formal charge on each atom that is present in the HCN molecule.

For calculating the formal charge, you need to remember this formula;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

You can see the bonding and nonbonding electrons of HCN from the image given below.

So now let’s calculate the formal charge on each individual atom present in HCN.

Formal charge on Hydrogen atom:
Valence electron = 1 (as it is in group 1 on periodic table) ^[1]
Nonbonding electrons = 0
Bonding electrons = 2

So according to the formula of formal charge, you will get;

Formal charge on Hydrogen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 1 – 0 – (2/2) = 0

So the formal charge on hydrogen atom is 0.

Formal charge on Carbon atom:
Valence electrons = 4 (as it is in group 14 on periodic table) ^[2]
Nonbonding electrons = 0
Bonding electrons = 8

So according to the formula of formal charge, you will get;

Formal charge on Carbon = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 4 – 0 – (8/2) = 0

So the formal charge on carbon atom is 0.

Formal charge on Nitrogen atom:
Valence electrons = 5 (as it is in group 15 on periodic table) ^[3]
Nonbonding electrons = 2
Bonding electrons = 6

So according to the formula of formal charge, you will get;

Formal charge on Nitrogen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 5 – 2 – (6/2) = 0

So the formal charge on nitrogen atom is 0.

Now you can see that all the atoms of HCN have 0 formal charge. 

This indicates that the overall HCN (hydrogen cyanide) molecule also has 0 charge and hence it is a neutral molecule.

I hope you have understood the above calculations for the formal charge of HCN (hydrogen cyanide). 

Check out some other related topics for your practice.

Related topics:
Charge on N2O (Nitrous oxide)
Charge of Germanium (Ge)
Charge on H2S
Charge on HBr
Charge on POCl3