Finding Oxidation Numbers for Polyatomic Ions

Determining the oxidation numbers of ions, whether monoatomic or polyatomic, involves understanding the rules for assigning oxidation numbers.

Oxidation number refers to the charge an atom would have if electrons were transferred completely.

RESOURCES
How to Find Oxidation Numbers (rules and examples): https://youtu.be/iSAwDJTLIKY
Oxidation Numbers Practice: https://youtu.be/hTjSNTOUcBQ
For Monoatomic Ions:

Know the Common Charge: Many elements have common charges. For example, chlorine typically has a charge of -1. For these ions that have the ionic charge given, it is equal to the oxidation number.

Be careful, some elements have multiple common charges. In such cases, the oxidation number can be deduced based on the compound in which the element is present.
For Polyatomic Ions:

In polyatomic ions, the sum of the oxidation numbers must equal the ion's charge. For MnO₄⁻, the overall charge is -1.

Determine the oxidation numbers for elements with fixed charges first. Oxygen typically has an oxidation number of -2, and hydrogen is +1.

In MnO₄⁻, the oxidation number for oxygen is -2 (four oxygen atoms), and the overall charge is -1. To find the oxidation number for manganese (Mn), set up an equation:

x + (-2 × 4) = -1, where x is the oxidation number of manganese.

In this case, x + (-8) = -1, so x = +7. Therefore, the oxidation number of manganese in MnO₄⁻ is +7.

Remember that these rules are general guidelines, and there might be exceptions or special cases. Always consider the context of the compound and apply the rules accordingly.

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Видео Finding Oxidation Numbers for Polyatomic Ions канала Wayne Breslyn (Dr. B.)