Beginner Topic 545 of 1102 Acids, Bases & Electrochemistry
Oxidation Number
The hypothetical charge of an atom if bonds were fully ionic.
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In-depth explanation of Oxidation Number
An oxidation number is a bookkeeping charge assigned to each atom by a set of rules, representing the charge it would have if all its bonds were fully ionic. Elements in their standard states are zero, monatomic ions equal their charge, oxygen is usually minus two, hydrogen is usually plus one, and the numbers in a species must sum to its overall charge. These values are not physical charges but are useful for tracking electron transfer in reactions. Changes in oxidation numbers identify which species are oxidized and reduced. They are indispensable for balancing redox equations and for naming compounds with variable valence.
Going deeper: Oxidation Number
Key ideas: Rules in priority order: elements are 0; monatomic ions equal their charge; sum equals overall charge; F is -1; group 1 is +1 and group 2 is +2; H is +1 (-1 in metal hydrides); O is -2 (-1 in peroxides). Then solve for the unknown: Mn in MnO4- is +7, Cr in Cr2O7 2- is +6, S in S2O3 2- averages +2.
Common mistakes and connections: Oxidation number is a bookkeeping device, not a real charge, and can be fractional (Fe3O4 gives +8/3 for Fe). Students forget that bonds between identical atoms do not change the count, or apply the O rule to OF2 or H2O2. Used to detect redox, identify what changes, and balance equations.
Visualization of Oxidation Number
Manganese ranges from 0 in the metal to +7 in permanganate; the number tracks how many electrons the atom has formally lost. The interactive lesson shows this as a live animation or chart.
Worked example and use case
In permanganate, MnO4-, manganese has an oxidation number of plus seven, since the four oxygens contribute minus eight in total.
Frequently asked questions about Oxidation Number
What is Oxidation Number?
The hypothetical charge of an atom if bonds were fully ionic.
Is Oxidation Number a beginner, intermediate or advanced topic?
Oxidation Number is a beginner topic in Acids, Bases & Electrochemistry. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Oxidation Number?
Study these earlier topics in Acids, Bases & Electrochemistry first: Henderson-Hasselbalch Equation, Buffer Capacity, Blood Buffer System.
What comes after Oxidation Number?
The next topics in Acids, Bases & Electrochemistry are Oxidation and Reduction.
Can I practise Oxidation Number with quizzes?
Yes. The interactive lesson includes a self-check question on Oxidation Number, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Where Oxidation Number fits in Acids, Bases & Electrochemistry
Oxidation Number is topic 35 of 105 in Acids, Bases & Electrochemistry.