The formal charge (F.C.) of an atom in a Lewis structure is calculated using the formula:
F.C. = [Total valence electrons] - [Total non-bonding (lone pair) electrons] - 21[Total bonding (shared) electrons]
For atom (1) Oxygen: Valence e−=6, Lone pair e−=4, Bonding e−=4.
F.C.=6−4−21(4)=0
For atom (2) Nitrogen: Valence e−=5, Lone pair e−=0, Bonding e−=8.
F.C.=5−0−21(8)=+1
For atom (3) Oxygen: Valence e−=6, Lone pair e−=4, Bonding e−=4.
F.C.=6−4−21(4)=0
For atom (4) Oxygen: Valence e−=6, Lone pair e−=6, Bonding e−=2.
F.C.=6−6−21(2)=−1
The formal charges are 0,+1,0,−1 respectively.
