The oxidation number, also known as the oxidation state, is a numerical value assigned to an element in a chemical compound that reflects the number of electrons an atom can gain, lose, or share when forming chemical bonds. It helps in understanding the distribution of electrons among atoms in a molecule and can indicate the degree of oxidation (loss of electrons) or reduction (gain of electrons) an atom has undergone in a reaction.
Key Points about Oxidation Numbers:
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Rules for Assigning Oxidation Numbers:
- The oxidation number of an element in its elemental form (e.g., O₂, N₂, Fe) is always 0.
- The oxidation number for monoatomic ions is equal to the charge of the ion (e.g., Na⁺ has an oxidation number of +1, Cl⁻ has -1).
- In compounds, hydrogen typically has an oxidation number of +1, oxygen usually has -2, and halogens often have -1, though exceptions exist.
- The sum of the oxidation numbers in a neutral compound is always 0, while in a polyatomic ion, it equals the charge of the ion.
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Purpose of Oxidation Numbers:
- They are used to identify oxidation and reduction processes in redox (reduction-oxidation) reactions, allowing chemists to track electron transfer.
- They help in writing and balancing chemical equations, especially in redox reactions.
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Application in Chemical Reactions:
- When the oxidation number of an atom increases, it signifies oxidation (loss of electrons).
- When the oxidation number decreases, it indicates reduction (gain of electrons).
Example:
In the compound \( \text{H}_2\text{O} \):
- Hydrogen (H) has an oxidation number of +1 (since there are two H atoms, contributing +2).
- Oxygen (O) has an oxidation number of -2.
- The overall charge is neutral: \( +2 + (-2) = 0 \).
Understanding oxidation numbers is crucial in various fields, including organic chemistry, biochemistry, and electrochemistry, as they provide insights into the nature of chemical reactions and the behavior of substances.
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