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

Br=7
F=7x5=35

Total=42

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

Br=12
F=8x5=40

Total=52

Bromine gets 12 electrons in order to make 5 bonds with surrounding atoms.

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

52-42=10e-

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

10e-/2= 5 bond pairs

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

42-10= 32e-=16 lone pairs

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

Lewis dot structure of BrF₅

Alternatively a dot method can be used to draw the lewis structure of BF₃.
Calculate the total valence electrons in BF₃ molecule.
Br=7
F=7x5=35

Total=42

Put Bromine in the center and five fluorine atoms on the sides.
Put a pair of electrons connecting the side atom with central atom.Pur remaining electrons on the side atoms.Make sure each side atom get 8 electrons to get octet state.( Bromine get expanded octet state)