Step 1: Find valence e- for all atoms. Add them together.
Step2: Find octet e- for each atom and add them together.
*Beryllium is exception to octet rule and get 4 electrons instead of 8.
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-)
4e-/2= 2 bond pairs
Step 5: Find the number of nonbonding (lone pairs) e-. Subtract step 3 number from step 1.
16-4= 12e-=6 lone pairs
Use information from step 4 and 5 to draw the lewis structure.
Beryllium goes in the centre.Make sure both fluorines get 8 electron.
Lone pairs are in green. Bond pairs are in purple.
Lewis dot structure of BeF2
Alternatively a dot method can be used to draw the lewis structure of BF3.
Calculate the total valence electrons in BF3 molecule.
Put beryllium in the center and fluorines on the sides.
Put a pair of electrons connecting the side atom with central atom.Put remaining electrons on the side atoms.Beryllium octer state is 4 electrons, so try to move the electrons to from fluprine to make it 8 for beryllium.