Master oxidation number rules with interactive practice
1. Free elements have oxidation state 0 (e.g., O₂, H₂, Na)
2. Monatomic ions have oxidation state equal to their charge
3. Hydrogen is usually +1 (except in metal hydrides where it's -1)
4. Oxygen is usually -2 (except in peroxides where it's -1)
5. Group 1 metals are always +1, Group 2 metals are always +2
6. Halogens are usually -1 (except when bonded to oxygen)
7. Sum of oxidation states equals the total charge on the species
• Enter answers as: Element: oxidation state (e.g., H: +1, O: -2)
• Separate multiple elements with commas
• Use + for positive, - for negative states
These equations frequently appear in VCE Chemistry. Practice identifying oxidation state changes! Click on "Half Equation" to reveal the equation.