The Lewis structure is a way of representing the elements and bonds between them. It is also called a dot-line diagram because it represents the bonds (pair of electrons that are shared) with a line and the free valence electrons with dots.
We must first check how many valence bonds each element has and check how many electrons are bonded and which are free. Recall that valence electrons are the electrons that are in the highest energy level.
We can see the valence electrons in the periodic table, it depends on the group to which the element belongs.
H: Group I ---> 1 valence electrons
C : Group IV ---> 4 valence electrons
N: Group V ---> 5 valence electrons
Cl: Group VII ---> 7 valence electrons
Therefore, the lewis structure will be:
Chlorine has a bond, so it shares an electron and Cl will have 6 free electrons represented by dots.
The central carbon has four bonds, a shared electron in each bond. So it has no free electrons.
The two hydrogens have their electron shared, there are also no free electrons.
The second carbon has two free electrons, but we must complete these free electrons, with bonds. So I will modify the above structure.
So there will be a triple bond from carbon to nitrogen.
And nitrogen will share 3 electrons with carbon and will be left with two free electrons.