Formal Charge Calculator
Calculate the formal charge of an atom from valence, lone-pair, and bonding electrons.
Number of valence electrons of the neutral atom (its main group number).
Total electrons in lone pairs (2 per lone pair).
Total electrons shared in bonds = 2 × number of bonds.
Formal Charge
Calculation Steps
What Is Formal Charge?
Formal charge is the hypothetical charge an atom would have if all bonding electrons were shared equally between the bonded atoms. It helps you evaluate Lewis structures and decide which resonance structure is most stable: the best structures usually keep formal charges as close to zero as possible. The sum of the formal charges on all atoms equals the overall charge of the molecule or ion.
The Formula
The formal charge of an atom is found from three quantities:
Formal charge = V − N − (B / 2)
- • V = valence electrons of the neutral atom
- • N = non-bonding (lone pair) electrons
- • B = bonding electrons (total shared in bonds = 2 × number of bonds)
Worked Examples
| Atom | V | N | B | Formal Charge |
|---|---|---|---|---|
| N in ammonium (NH₄⁺) | 5 | 0 | 8 | +1 |
| O in water (H₂O) | 6 | 4 | 4 | 0 |
| O in hydroxide (OH⁻) | 6 | 6 | 2 | −1 |
Note: Formal charge is a bookkeeping tool, not a measured physical charge. It assumes electrons in a bond are split evenly regardless of electronegativity, so it differs from the oxidation state. Use it to compare and rank candidate Lewis structures, not as an exact measure of charge distribution.