Step 1: Find valence e- for all atoms. Add them together.

H:1
C:4
N:5

Total=10

Step2: Find octet e- for each atom and add them together.

H:2
C:8
O:8

Total=18

Step3: Gives you bonding e-. Subtract step 1 total from step 2

18-10=8e-

Step 4: Find number of bonds by diving the number in step 3 by 2(because each bond is made of 2 e-)

8e-/2= 4 bond pairs

Step 5: Find the number of nonbonding (lone pairs) e-. Subtract step 3 number from step 1.

10-8= 2e-=1 lone pair

Use information from step 4 and 5 to draw the lewis structure.

Carbon  goes in the centre.Make sure carbon and Nitrogen get 8 electrons to fulfil octet rule.

Lewis dot structure of HCN

Alternatively a dot method can be used to draw the lewis structure of BF₃.
Calculate the total valence electrons in BF₃ molecule.
H:1
C:4
N:5

Total=10

Put carbon in the center and hydrogen and oxygen on the sides.
Put a pair of electrons connecting the side atom with central atom.Put remaining electrons on the side atoms.Move electrons fron oxyfgen so that both carbon and oxygens get octet state.

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