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Oxidation State

Last updated: August 10, 2019

What Does Oxidation State Mean?

Oxidation state is a number assigned to an element in a compound. This number describes oxidation-reduction reactions, and balancing redox chemical reactions.

The concept of oxidation states expresses the combining power exercised by elements in their compounds and is thus related to their valences. It can be illustrated by comparing the ratios of metal atoms to oxygen atoms in some examples of metal oxides.

The more electronegative element in a substance is given a negative oxidation state. The less electronegative one is given a positive oxidation state.

Oxidation state is also known as oxidation number.


Corrosionpedia Explains Oxidation State

Oxidation state shows the total number of electrons which have been removed from an element (a positive oxidation state) or added to an element (a negative oxidation state) to get to its present state. It is an indicator of the degree of oxidation or reduction of an atom in a chemical compound. Oxidation increases oxidation state and reduction decreases oxidation state. For pure elements, the oxidation state is zero.

When an oxidation number is assigned to the element, it does not imply that the element in the compound acquires this as a charge, but rather that it is a number to use for balancing chemical reactions. Oxidation state is commonly used to determine the changes in redox reactions and is numerically similar to valence electrons, but different from formal charge. Formal charge determines the arrangement of atoms and the likelihood of the molecule existing.

Since oxidation state of an element changes when it absorbs or releases electrons by transfer of electrons between chemical species, the products of corrosion often reflect the metal's natural state, both physically and in accordance to oxidation states. Corrosion is a process through which metals in manufactured states return to their natural oxidation states. This process is a reduction-oxidation reaction in which the metal is being oxidized by its surroundings, often the oxygen in air. The tendency of metals to corrode is related to the low stability of the metallic state. Metals occur either in the pure metallic state, the zero oxidation state, or in the form of compounds with other elements.



Oxidation Number

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