Formal Charge Calculator
FC = valence − lone electrons − bonds, per atom.
Work out Formal Charge. FC = valence − lone electrons − bonds, per atom. Shows every step's contribution, not just the total.
The group number for main-group elements: C is 4, N is 5, O is 6, halogens 7.
Count electrons, not pairs — two lone pairs is 4.
Count bonds, so a double bond is 2 and a triple is 3.
Formal charge
+1
1 away from zero
Formal charge counts each bonding pair as split evenly, which is a deliberate fiction — it ignores electronegativity entirely, and that is what makes it useful for comparing Lewis structures rather than for predicting real charge distribution. The best structure minimises formal charges, and where a charge is unavoidable it puts the negative one on the most electronegative atom. Do not confuse it with oxidation number, which makes the opposite assumption and gives every bonding pair to the more electronegative atom. Carbon in methane has a formal charge of 0 and an oxidation number of −4.
How the Formal Charge Calculator works
Enter the valence electrons, non-bonding electrons and number of bonds for one atom in a Lewis structure. Formal charge is the tool for choosing between competing structures — the best one keeps charges near zero and puts any negative charge on the most electronegative atom.
Also known as: lewis structure formal charge · how to calculate formal charge · best lewis structure calculator · formal charge formula
Frequently asked questions
How do I calculate formal charge?
Formal charge = valence electrons − non-bonding electrons − number of bonds. Nitrogen in ammonium has 5 valence, 0 lone and 4 bonds, giving +1.
What is the difference between formal charge and oxidation number?
They make opposite assumptions. Formal charge splits every bonding pair evenly; oxidation number gives the whole pair to the more electronegative atom. Carbon in methane has a formal charge of 0 and an oxidation number of −4.
Which Lewis structure is best?
The one with formal charges closest to zero. Where charges are unavoidable, the negative one should sit on the most electronegative atom, and adjacent atoms should not carry like charges.
Do I count electrons or pairs?
Electrons. Two lone pairs is 4 non-bonding electrons. Bonds are counted as bonds though, so a double bond is 2 — which is the same as counting its shared electrons and halving.
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