Electron mismatch
If the drawing uses too many or too few electrons, stop and correct the count before changing bonds.
Final-answer verification
How to Check a Lewis Structure
A finished drawing is not automatically correct. Verify the electron budget, connectivity, valence shells, formal charges and geometry in a fixed order.
- Recalculate total valence electrons.
Add each atom's contribution and apply charge. Your dots and bonds must use exactly this total.
- Confirm the atomic connectivity.
The least electronegative non-hydrogen atom is often central, but acids and organic functional groups require known connectivity patterns.
- Check duet, octet and exception rules.
Hydrogen needs two electrons. Most second-period atoms need eight. Identify legitimate incomplete, odd-electron or expanded cases.
- Calculate every formal charge.
The formal charges must sum to the net charge. Compare alternative bond patterns and charge placement.
- Separate Lewis structure from 3D shape.
After the electron diagram is correct, count electron domains and apply VSEPR to obtain molecular geometry.
Central atom lacks an octet
Consider whether a terminal lone pair should form a multiple bond, or whether the species is a valid octet exception.
Charges do not add correctly
Recalculate formal charge atom by atom using FC = V − N − B/2.
Resonance is missing
Look for equivalent terminal atoms where a pi bond or negative charge can occupy more than one position.
Shape was guessed too early
Complete lone pairs first; they count as electron domains even though they are not visible atoms.
Formula is ambiguous
For organic formulas and isomers, identify connectivity before attempting a unique Lewis structure.