Question

How to draw Lewis structure of $HCN$?

Answer 1

Hint: $HCN$ is known by the name hydrogen cyanide and sometimes by prussic acid. It is colorless, extremely poisonous and flammable liquid. It is a weak acid. Hydrogen cyanide is a linear molecule having a triple bond between carbon and nitrogen.

Complete answer:
Lewis structure basically tells us how the electrons are paired. In this every dot represents an electron and pair of dots between chemical symbols for atoms represents the bond. The main steps of draw a Lewis structure are as follows:
1. Calculate the valence electrons present in the molecule this can be calculated by adding the valency of individual atoms in the given molecule. In case of $HCN$ valence electrons are 10 as Hydrogen have valency 1, Carbon 4 and Nitrogen 5.
2. Now we have to find the octet electron for each atom and add them together so the octet electron for hydrogen, oxygen and nitrogen are 2, 8 and 8 respectively so the total octet electrons are 18.
3. After that we have to find the bonding electrons which can be calculated by subtracting the octet electrons from valence electrons i.e. $18-10=8$
4. Now we have to find the number of bonds which can be calculated by dividing the bonding electrons by 2 = $\dfrac{8}{2}=4$ bonds.
5. The rest bonds are termed as non-bonding pairs which can be calculated by subtracting the bonding electrons from valence electrons i.e. $10-8=2$ which describes 1 lone pair.
By this we can draw the Lewis structure of $HCN$ which can be shown as follows:

Note:
If we know the molecular formula of any compound we can easily draw its Lewis dot structure which is also known by the name electron dot structure. These diagrams generally describe the chemical bonding between atoms in a molecule and also display the total number of lone pairs present in each of the atoms.