Formal Charge vs Oxidation Number: The Difference
Both numbers sit on the same atom in the same molecule, and both look like charges. Yet carbon in CO has a formal charge of −1 and an oxidation number of +2 — opposite signs on the same atom. That isn't a contradiction. They're answers to two different questions, and each one is deliberately, usefully wrong in its own way. The short answer: formal charge splits every bonding pair straight down the middle, giving one electron to each atom, and asks what charge each atom would then carry. Oxidation number does the opposite extreme — it gives both electrons of every bond to the more electronegative atom. Formal charge is for picking the best Lewis structure; oxidation number is for tracking redox. Quick comparison at a glance Feature Formal charge Oxidation number How bonds are split Evenly — one electron each Entirely to the more electronegative atom Assumption made Bonds are perfectly covalent Bonds are perfectly ionic Electronegativity used? No Yes — it decides who ta...