HCN is called Hydrogen cyanide. First we need to count the total number of valence electron. We just add the valence electron of each atom involved.
C = 4
O = 5
H = 1
Next, we have to assign the central atom; In this case it is C.
Now we have to connect the atoms and form a bond. We have now C---N (triple bond) , and a C-H bond
Finally, we have to distribute The remaining electrons on N provided that it follows the octet rule.
` H -C-=N: `
HCN contains a triple bond and therefore it is a linear molecule. Linear molecules have 180 degrees bond angles.