Step 1: Find valence e- for all atoms. Add them together.
Step2: Find octet e- for each atom and add them together.
Step3: Gives you bonding e-. Subtract step 1 total from step 2
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.
12-8= 4e-=2 lone pair
Use information from step 4 and 5 to draw the lewis structure.
Carbon goes in the centre.Make sure carbon and oxygen get 8 electrons to fulfil octet rule.
Lewis dot structure of H2CO
Alternatively a dot method can be used to draw the lewis structure.
Calculate the total valence electrons in the molecule.
Put carbon in the center and arrange hydrogen and oxygen atoms on the sides.Arrange electrons until both carbon and oxygen get 8 electrons.( hydrogen octet state is 2)