How do I show HCN with the lewis dots
1 H = 1 x 1e each = 1 electron.
1 C = 1 x 4e each = 4 electrons.
1 N = 1 x 5e each = 5 electrons.
total = 10 electrons.
How many do we need? We need 8 for C, 8 for N, and 2 for H; therefore, we need our 10 electrons to do the job of 18 electrons. The difference is 18-10 = 8 and if we have electrons paired that is 8/2 = 4 bonds.
H:C:::N:
This gives us 4 bonds, C has 4 (which is usual), H has 1 (which is usual), N has 3 (which is usual), and we have used 10 electrons. Furthermore, we have two electrons around H, 8 around C and 8 around N. Have you learned how to do the formal charge. That is zero on H, zero on C, and zero on N.