Formal charge is the difference between the number of valence electrons of the atom in free state and the lewis structure. Here we will discuss how to calculate the F.C. on the atom in a molecule.
What is Formal Charge
Formal charge is the difference between the number of valence electrons of the atom in free state and the lewis structure.
[ F.C. on atom in a molecule / ion ] = [ Total number of valence electrons in the free atom ] – [ Total number of electrons of lone pair (non bonding electrons ] – 1/2 [ Total number of shared electrons (bonding electrons ) ]
F.C. = V – L – 1/2 S
Calculate the F.C. on O atom in O3 molecule
- There are 3 types of O atoms in O3 as number 1,2 and 3
- F.C. on end O number 1 = F.C. = V – L – 1/2 S = 6 – 4 – 1/2(4) = 0
- Formal charge on central O atom number 2 = 6 -2 – 1/2 (6) = + 1
- F.C. on end O number 3 = 6 -6 – 1/2 (2) = -1
Calculate the Formal charge on S in HSO4- ion
- Applying the F.C. formula F.C. = V – L – 1/2 S
- F.C. on S atom in HSO4^- = 6 – 0 – 1/2 (8) = 6 -4 = +2
Calculate the F.C. on Cl in HClO4
F.C. on Cl in HClO4^- = 7 – 0 – 1/2 ( 8 ) = +3
Calculation of F.C. on atoms in 1) carbonate ion and 2) nitrite ion
F.C. on C atom in carbonate ion = 4 – 0 – 1/2 (8) = 0
Formal charge on doubly bonded O atom = 6 -4 -1/2 (4) = 0
F.C. on single bonded O atom = 6 – 6 – 1/2 (2) = -1
F.C. on N atom in nitrite ion = 5 – 2 – 1/2 (6) = 0
Formal charge on doubly bonded O atom = 6 – 4 – 1/2 (4) = 0
F.C. on singly bonded O atom = 6 – 6 – 1/2 (2) = -1
Check out the post of how to draw the Lewis structures here
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