Formal charge is equal-share electron accounting
Formal charge, oxidation state and partial charge answer different questions.
Key knowledge
In a Lewis structure, formal charge assigns each atom its nonbonding electrons and half of its bonding electrons, then compares that count with the neutral atom's valence-electron count. Formal charges sum to the species' net charge. They are bookkeeping values, distinct from partial charge and from oxidation state's ionic approximation of heteronuclear bonds.
Values and equations
FC = V - L - B/2
- FC
- formal charge number for an atom in the specified Lewis structure 1
- V
- neutral atom's valence-electron count 1
- L
- nonbonding electron count assigned to that atom 1
- B
- bonding electron count incident on that atom 1
Conditions and scope
- Specify the Lewis representation and valence-electron counts; L counts nonbonding electrons, not lone pairs.
- A formal charge does not by itself measure an atom's actual electron-density distribution or prove which resonance contributor dominates.
Sources · 3
References
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Evidence and review
Inspected §7.4 Calculating Formal Charge, equation, charge-sum check and bookkeeping limitation. Read IUPAC's indexed term bodies for formal charge and oxidation state's ionic approximation; direct term retrieval failed. The calculation is grounded in the directly read textbook body.
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