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

Be:2
F:7x2=14

Total=16

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

Be:4*
F:8x2=16

Total=20

*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

20-16=4e-

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.
Be:2
F:7x2=14

Total=16

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.

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