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-)
6e-/2= 3 bond pairs
Step 5: Find the number of nonbonding (lone pairs) e-. Subtract step 3 number from step 1.
8-6= 2e-=1 lone pair
Use information from step 4 and 5 to draw the lewis structure
Lewis dot structure of PH3
Alternatively a dot method can be used to draw the lewis structure.
Calculate the total valence electrons in the molecule.
Put phosphorous in center and arrange hydrogen atoms on the sides.Arrange electrons until phosphorous get 8 electrons.