Oxidation Number

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For all chemical reaction (base particles group one way going into the reaction are grouped differently out of the reaction where at least one grouping is different). As you know the total mass, total number of atoms, total number of each type of atom and total energy must be conserved. There is another conservation we have not talked about. Number of electrons moving must also be conserved in a chemical reaction.

So we must have a system of keeping track of electrons in a chemical reaction. Well, is that not what "charge" does? If an element gains electron, it become an anion with a "negative" charge (i.e. 1- charge). Or an element can lose electrons to become a cation with a "positive charge" (i.e. 1+ charge). Yes, that is correct but it does not explain all substances. What about when electrons are shared by 2 element (like in a chemical bond). These elements in the molecular compounds (or polyatomic ion) do not have charge since they did not lose or gain electron, the electrons are being shared.

So to be able to incorporate sharing electron substances, we have invented a new electron accounting system called, Oxidation Number.

The rules for assigning oxidation numbers (every atom no matter what type of substance it is in gets one), click here OxidationNumber (also need ElectronegativityTable).
- These rules are good for understanding exceptions and general understanding.

To actually assign oxidation number, I believe the following is a better way of explaining the procedure,[Flowchart for Assigning Oxidation Numbers] .
- This handout include the general flowchart (sets of questions to ask) and an example of each major type of substance
- Watch this [You Tube video on Assigning Oxidation Numbers] If you are using Edpuzzle, need to watch Chem328AssigningOxidationNumberFlowchartVideo
  - Make sure you have the above links open before watching the video (include ElectronegativityTable)

Then try to assign oxidation numbers from this homework, Oxidation Number HW
- Answers to Oxidation Number HW